Author: Maddie Van Beek


Last week, we learned about Newton’s First Law of Motion, or the Law of Inertia. You learned that an object in motion will stay in motion, or an object at rest will stay at rest, unless affected by an outside force. If you missed us last week, check out http://discoveryexpress.weebly.com/…/demonstrating-the-law-…. 




Newton’s Second Law tells us that the acceleration of an object--as produced by a net force--is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. 




What does that even mean?! 




It can be simplified into this equation:




F = m * a




F = force

- Force is measured in Newtons. 

m = mass

- Mass is measured in kilograms. 

a = acceleration 

- Acceleration is measured in meters per second squared. 







Before you try using this equation, here’s a great example from howstuffworks.com. 

Let’s say you are trying to calculate the acceleration for this dog sled. As you can see, the force is 100 newtons, and the mass is 50 kilograms. 




Before you plug the numbers into the equation, isolate acceleration, since that is what you are trying to find. 




F = m * a




Take the force divided by mass to get acceleration by itself. 




a = F/m




Next, plug the numbers into the equation. 




a = 100N/50kg




Now, divide! 




a = 2 m/s^2 




You’ve calculated the acceleration of the sled! 




But what if another dog that pulls with equal force is added to the team? 

Try calculating the acceleration this time! 




F = 200 N

m = 50 kg

a = ? 




a = F/m

a = 200 N/50 kg

a = 4m/s^2




What would have happened if you had doubled both the force and the mass? 




F = 200 N

m = 100 kg

a = ? 




a = F/m

a = 200 N/ 100 kg

a = 2m/s^2




You’d be right back to an acceleration of 2m/s^2.  




This example demonstrates how the acceleration is proportional to the force. 

The picture above illustrates the idea of net force. If two equal forces are opposing each other, the net force becomes zero. In this picture, you see that there are two dog sled teams pulling with a force of 200 N on either side of the sled, so the net force is zero. This means that the sled would not move. If the sled team on the right were bigger and were pulling with a force of 300 N, then the sled would move to the right. Make sense? 




You now have plenty of information to complete the practice equations and the activity below, but for further description of Newton’s Second Law of Motion, check out this helpful video from KhanAcademy: 

Now that you have seen a few demonstrations, let’s practice:




1. Erin and Andrew are playing tug of war. Erin is pulling to the right with a force of 100 N. Andrew is pulling to the left with a force of 200 N. What is the net force? What direction would they move? 

2. Grady is pulling a wagon that has a mass of 30 kilograms. Grady is pulling with a force of 300 N. What is the acceleration? 


3. Ashley is pushing a stroller that has a mass of 20 kilograms. The stroller is accelerating at 3 m/s^2. 
Use F = m * a to find the force. 


4. Deidre is pulling her puppy’s leash with a force of 50 N, but the puppy is pulling in the opposite direction with a force of 25 N. What is the net force? 

5. Josiah is pushing a shopping cart with a force of 75 N at a rate of 1 m/s^2. What is the mass of the shopping cart? 




Activity




YOU WILL NEED:

• 2 marbles of the same size, but different masses. Both should be lighter than the ball bearings. 
• 2 identical ball bearings
• Ramp (could be constructed out of poster board) 
• Tape Measure
• Scale
• Stopwatch

Here’s what to do!

1. Use the scale to determine the mass of each marble and ball bearing. Record these masses in your observation journal. 
2. Use a tape measure to create two meter-long ramps. You could use heavy poster board to make the ramp. Make sure you fold up the sides so the marble won’t roll off. 
3. Place one end of the first ramp on top of a stack of books to create an approximately 10 degree incline. 
4. Mark the first ramp at 30cm and 60cm. 
5. Place the end of the second ramp at the bottom of the incline of the first ramp. Make sure the marble will be able to roll smoothly from one ramp to the next. You could place a piece of tape to connect the two ramps and make sure it’s a smooth transition. 
6. Now that you’ve made your ramp, place one ball bearing at the base of the first ramp, right where the second ramp starts. Here is what your final set-up should look like: 

1. Place the marble with the smallest mass at the top of your ramp. What do you think will happen when it hits the ball bearing? Try it out! 
2. As you can see, the ball bearing moves when it is struck by the marble. Think back to Newton’s First Law, an object at rest stays at rest until enacted upon by an outside force. 
3. Try this again, except this time, use the stopwatch to time how long it takes the marble to travel from the top of the ramp to the ball bearing at the bottom of the ramp. 
4. Do this three times and then calculate the average time. 
5. Repeat step 8 and 9 with first the second marble and then the ball bearing. 
6. Next, repeat step 8-10, except start at the 30cm mark. 
7. Last, repeat steps 8-10, except start at the 60cm mark. 

Record your data and calculate the acceleration in this chart: 
 

To calculate acceleration, subtract the ball’s initial speed (zero) from its final speed and divide by the time it took to hit the target ball. 




Example: 

Speed:          100cm/2sec

Simplified:      50cm/sec

Acceleration:  (50cm/sec - 0cm/sec) / 2 sec

                      25cm/sec^2




Part 2

What’s happening when the first ball hits the second ball? 

So now that you’ve determined acceleration for each impact ball, let’s focus on what happens when each ball hits the target ball bearing at the bottom of the first ramp. As you have seen, the force of the accelerating ball causes the once-stationary target ball to move. 




How do you think the mass of the impact ball affects the time it takes the target ball to travel down the second 1m ramp once it is struck? 




Let’s find out! 




1. Just as you did before, start with the lightest marble at the top of the ramp. This time, you are using the stopwatch to measure the time it takes the target ball to travel from its starting point to the end of the second 1m ramp. You will start the stopwatch once the target ball is struck and stop the stopwatch once it reaches the 1m mark. 


2. Repeat step 1 three times and record the average time. 


3. Repeat steps 1-2 with the second marble. 


4. Repeat steps 1-2 with the other ball bearing. 


5. Record in the table below: 

Record your observations. Did the mass of the impact ball affect the average time the target ball took to travel 1m? Why do you think this is? 

You should have found that the more mass the impact ball had, the faster the target ball rolled 1 meter. This explains Newton’s Second Law: Larger mass means larger force, which then means larger acceleration. This demonstrates how the variables of mass, acceleration, and force are proportional with one another. 




Extension: 

Now that you have the mass and the acceleration of the impact balls from part one, you can calculate the force with which they hit the target ball bearing. Remember, the force is found by multiplying the mass and the acceleration. 

References

http://science.howstuffworks.com/innovation/scientific-experiments/newton-law-of-motion3.htm

http://www.physicsclassroom.com/class/newtlaws/Lesson-3/Newton-s-Second-Law

http://swift.sonoma.edu/education/newton/newton_2/html/Newton2.html

http://www.physicsclassroom.com/class/1DKin/Lesson-1/Acceleration

Author: Maddie Van Beek

Today we are going to be learning about Newton’s First Law! Physicist Sir Isaac Newton came up with the three laws of motion. The basis of the first law is:

An object at rest stays at rest 


AND 


An object in motion stays in motion 


UNLESS


Acted upon by outside sources. 

This is often called the law of inertia.  Inertia is defined as a tendency to remain unchanged, and continue in its existing state of rest or uniform motion unless changed by an external force. Basically, this means that objects will keep on doing what they’re doing unless an outside force affects their state of motion. 

Can you think of this happening in the real world? I can! For example, I take coffee to my job with me every day. When set my coffee mug in my cup-holder in my car, the coffee in the mug is at rest. When I accelerate out of my driveway, the car goes from being in rest to being in motion. But there is no force acting on the coffee in my mug, so it wants to stay at rest. Consequently, the mug moves forward along with the car, and the coffee sloshes out of the mug. 


To learn more about Newton’s Laws, check out the link below! 

Today, we are going to focus on the first part of the law: An object at rest stays at rest.


The video below will demonstrate our focus today. 

Reflect:

• What happened in this demonstration? 
• How was Newton’s First Law at work here? 
  

Want to try this out on your own? 

YOU WILL NEED:

• Crochet hoop
• Pen cap (or other small object)
• Bottle or vase
• Water

Here’s what to do! 

1. Fill the bottle with water. 
2. Place the crochet hoop on top of the bottle’s opening. 
3. Carefully place the pen cap on top of the crochet hoop so that it is balanced directly over the mouth of the bottle. 
4. Use one finger to quickly pull the crochet hoop directly sideways. 
5. When this happens, the pen cap should fall straight down into the bottle. 
6. If this didn’t work for you on the first try, don’t get frustrated! Just try it out again. If you continue to have difficulties, try using a bottle with a wider mouth. 

Here’s another way to demonstrate the same concept. These students used a paper plate, a toilet paper roll, and a glass instead of the crochet hoop and bottle. 

In the following video, two students came up with different way to demonstrate Newton’s First Law. 

Want to try out this method? 


YOU WILL NEED: 

• Two identical bottles
• Water
• A dollar bill 

Here’s what to do!

1. Fill one bottle with water. 
2. Place the dollar bill over the mouth of the bottle with water in it. 
3. Balance the second bottle over the first bottle with the dollar bill in between the mouths of the bottles. 
4. While carefully keeping the mouths of the bottles aligned, flip them over and carefully set them down so that the bottle with the liquid is on top. 
5. Now, grab the end of the dollar bill and quickly pull it out! 
6. What happens? The two bottles are stationary and the liquid from the top bottle falls into the bottom bottle. 

Reflect: How did this demonstration show you Newton’s First Law? What were some similarities between this demonstration and the first one you watched? Differences? 




These were just two ways to demonstrate Newton’s First Law at work. What other ways can you think of to demonstrate Newton’s First Law? Brainstorm some ideas and try them out! We’d love to hear about them! 




References: 

• http://www.scholastic.com/teachers/article/40-cool-science-experiments-web
• <iframe width="420" height="315" src="https://www.youtube.com/embed/uOSBC0SXVR4" frameborder="0" allowfullscreen></iframe>
• <iframe width="420" height="315" src="https://www.youtube.com/embed/5k2hhEFNxdM" frameborder="0" allowfullscreen></iframe>
• http://www.physicsclassroom.com/class/newtlaws/Lesson-1/Newton-s-First-Law

Author: Maddie Van Beek


Why is soap important? I’m sure you have the idea ingrained in your head that you need to wash your hands before dinner, before cooking, after using the restroom... but why?

Learn more about the importance of hand-washing in the link below!


Hand-washing Dos and Don'ts



Today, our activities are all about soap! First, we will see what happens when we put bar soap in the microwave. What do you think will happen? Next, we will try making a variety of soaps to see which ingredients do the best job of washing your hands! 

YOU WILL NEED:

• A variety of bar soaps. Pick 3-4 different brands of bar soap, but one must be Ivory. 
• Bowl
• Water
• Microwave
• Plate

HERE’S WHAT TO DO!

1. Unwrap each bar of soap. 
2. One by one, place each bar of soap in a bowl of water and record what happens.
3. Do you any of them float? Do they all sink? 
4. You should have noticed that the Ivory bar floats. Why is it that Ivory floats while others sink? Make a hypothesis!
5. You might have guessed that there was an air pocket in the Ivory soap... cut it open and find out.
6. Did you find an air pocket? Nope! What could it be? 

Explanation: The truth is, Ivory soap IS filled with air, but only in minuscule amounts. There are no large air pockets, but there are tons of tiny little air bubbles whipped into the soap during production. These little air bubbles are what make Ivory soap float. 


Now, let’s see what happens when we put Ivory soap in the microwave!


HERE’S WHAT TO DO!

1. Place the Ivory soap on a paper towel in the microwave.
2. Set the microwave on HIGH for 2 minutes.
3. Observe amazingness! What happened?!
4. You should have seen the Ivory soap expand much like a marshmallow! Why do you think this happened? Clue: Think about the air bubbles. 
5. This effect is actually a demonstration of Charles’ Law. Charles’ Law states that volume of gas will increase as temperature increases. How did you see that demonstrated when you put the Ivory soap in the microwave? Explain how your observations relate to Charles’ Law. Learn more about Charles’ Law HERE. 

Here’s video that demonstrates what should have happened:

Let’s switch gears--we are now going to make our own soap! Rather than making entirely homemade soap, we are going to take a quick shortcut that will allow you to alter plain bar soap and compare the additives that you choose to use. 

YOU WILL NEED:

• Bar soap
• Spoon
• Small microwavable bowl
• Muffin tin
• Masking tape
• Marker
• Additives of your choice--could include milk, honey, oatmeal, sugar, cinnamon, etc. 

HERE'S WHAT TO DO!

1. First, you need to buy a few bars of fragrance free, dye free soap. 
2. Next, decide which ingredients you would like to add to your soap. A common combination is milk and honey. You could also try using oatmeal or sugar as an exfoliant. You decide! How might adding these ingredients affect the soap’s hand-washing effectiveness? Write down your hypotheses for each combination you create. 
3. Next, you will melt the bar soap down to a liquid form. Be careful--it does get very hot when melted! Stop the microwave every 30 seconds and stir until the soap is completely melted. 
4. Mix in your additives with the melted bar soap. Make sure you save one piece of bar soap to use as a control. 
5. Pour the bar soap mixture into a muffin tin. Make sure you label the tin with masking tape and a marker so you know which soap is which. For example, you might label the row, “Honey Oatmeal,” “Honey Milk,” or “Cinnamon Sugar” depending on what you mixed with your soap.
6. Let the soap dry completely. This will take a few hours.
7. Now that your soap is finished, try it out!
8. Find a few friends to help you determine which soap is most effective. Use a washable marker to draw a line on your friends’ hands. Have each of them use a different soap for 1 minute. Record observations. Which soap washed the marker off most completely? 
9. Repeat step 7, except have each friend use a different soap than the one before. Did you get the same results?
10. Repeat step 7, except have each friend use a different soap than the last two times. Did you get the same results? Continue until each friend has used each soap, including the original, unchanged bar soap. 
11. Repeat steps 7-9, except use permanent marker. Did you find the same results?
12. Repeat steps 7-9, except use pen. Did you find the same results? 
13. Create a table or graph to represent which soap was most effective in removing the marker, permanent marker, and pen.  

Check out our Clean Hands Challenge for another fun experiment about hand-washing! 








Resources:

http://www.stevespanglerscience.com/lab/experiments/soap-souffle

http://www.chm.davidson.edu/vce/gaslaws/charleslaw.html

http://www.wikihow.com/Make-%27Melt-and-Pour%27-Soap

http://www.education.com/activity/article/Make_Soap_middle/

Sound is everywhere.  Music, birds singing, cars and people on the street, nearly everything around us makes some sound.   But what is sound really and how is it created?

Sound is created by moving or vibrating objects.  This vibration pushes and pulls on the air molecules close to the object, which then push and pull on the molecules next to them, which push and pull on the air molecules next to them, getting further and further from the object.  This phenomenon is called a longitudinal wave (a.k.a. compression wave).  A good way to visualize this is using a slinky: if you hold a slinky in mid air or lay it out on a table, and tap one end, the first coil of the slinky will push and pull on the second coil, which will push and pull on the third coil, and so on.  This causes a wave that moves all the way through the slinky, even though the slinky itself does not move. 

Here is a YouTube video showing the slinky demonstration, taken and uploaded by Trevor Murphy.  Thanks to Mr. Murphy for sharing this excellent demonstration!

When objects vibrate, they tend to do so at a certain frequency; that is, they move back and forth—or oscillate—at a certain speed.  This pushes and pulls on the air at a particular speed, causing the wave generated to have a certain sound.  This is how a tuning fork works.  A tuning fork is a two pronged, U-shaped fork that vibrates with a certain frequency (and therefore a certain sound) when struck.  They produce a very consistent sound corresponding to a certain note, and thus are used by piano tuners to make sure the instrument is producing the right notes. 

Just like a tuning fork, U-shaped glasses made of thin glass also tend to vibrate at a certain frequency, depending on whether they contain any liquid.  A wine glass is an excellent example; tap a wine glass gently with your finger, and it will usually produce a ringing sound.  This is caused by the vibration of the glass, and corresponds to a certain note just like the tuning fork.  In fact, if you play this note at the wine glass loudly enough, the glass will vibrate so hard it will shatter!  Here is another YouTube video demonstrating this phenomenon, which we don’t recommend you try at home! 

Thanks to Harvard Natural Sciences Lecture Demonstrations for producing and uploading this video!

While you shouldn’t try to shatter glass at home, there is another way you can experience the vibration of a wine glass using your finger and a little water.  This will cause the glass to oscillate at a particular frequency, creating a certain note. 

TRY IT!!

Here’s what you’ll need:

1.       A stemmed wine glass, the thinner the glass is the better.

2.       A small amount of water (just enough to get your fingers wet)

Here’s what you need to do:

1.       Set the wine glass on a flat surface.  Hold the very bottom of the stem to keep the glass still.

2.       Wet your fingers well.  This allows your fingers to glide along the rim of the glass easily.

3.       Slowly start running your fingers around the rim of the glass, using the part of your finger between the tip and the second knuckle.

You may have to practice a little before the wine glass begins to make sound.  Keep trying!

CHALLENGE YOURSELF!

How many notes can you make with your wine glasses?  If you add water to the glasses, they will create a different note when you run your finger over the rim, depending on how much water you add.  See if you can create a whole scale or play a song!  With a lot of practice, you will eventually be able to play like Robert Tiso, who in the video below plays Dance of the Sugar Plum Fairy by Tchaikovsky using only glasses and water!  Thanks to Robert Tiso for sharing this amazing video—ENJOY!

We see air planes nearly every day, flying in and out of airports, leaving vapor trails across the sky.  How can such a large, heavy object fly?  After all, even the smallest of air planes is over 1500 pounds!  We can find the answer in something called Bernoulli’s principle.

To fully understand Bernoulli’s principle, we first have to understand air pressure.  There is air all around us all the time, and this air is always pressing on us.  Because the air is pressing on us evenly from all directions, we usually don’t notice it. 

When objects move through the air they must push it out of the way,  just as they would if they were traveling though a liquid or a solid.  As it is pushed out of the way by the object, the air moving around the object must move faster than the rest of the surrounding air.  Think of it this way:  imagine a shallow swimming pool full of ping pong balls.  If you run from one end of this pool to the other end through the ping pong balls, the balls you push out of the way as you run will need to move faster than the balls farther away from you.  This is exactly what happens to the air as an object moves through it—the air molecules are like the ping pong balls, being pushed out of the way! 

As the air molecules move faster, they are not able to exert as much air pressure—and this is where Bernoulli’s principle comes in.  Bernoulli’s principle states that an increase in the speed of a fluid (either a liquid or a gas) is accompanied by a decrease in pressure.  Therefore, as this fluid moves from an area of high pressure to an area of low pressure, it will speed up—this is why when the atmospheric pressure drops, the wind begins to blow! 

This also means that as fluid moves faster, its pressure—that is, the amount of force with which it pushes against other things—drops.  This effect is the reason why airplanes can fly.  To understand this, we need to look closer at an airplane’s wings.

The wings of an airplane have a very particular shape:  the top of the wing is more curved than the bottom of the wing.  Because of this extra curve on top, the air flowing around the wing has farther to travel around the top of the wing than the bottom of the wing.  This extra distance means the air travels faster, reducing the pressure over the top of the wing.  The reduced pressure on top of the wing allows the pressure on the bottom of the wing to push the airplane upward, causing it to fly!

TRY IT!

You can demonstrate Bernoulli’s principle for  yourself with a very simple experiment.  All you need is a sheet of paper (at least 5 inches wide and 8 inches long), and some clear tape!

Here’s what to do:

1.       Take your sheet of paper, and fold it along its width.  The fold should be about one inch off the middle of the sheet.

2.       Bring the edges of the paper together, and hold them in place.  Use your tape to tape the edges together.

3.       Blow across the edges of the paper, and observe what happens!

What happened when you blew across the paper?  Did it move?  If so, which way?  Be sure to write down all your observations!


References for further reading:

1)      Lord, M.  “Lesson: Get a Lift!”.   eGFI.  March 25, 2011.  teachers.egfi-k12.org/get-a-lift/

Have you ever bumped your head or twisted your ankle, and had a nurse put a cold pack on your injury?  You may have noticed he or she did not take the pack out of the freezer—the pack had no ice in it...yet it was still cold!  Or, have you ever been outside on a cold day and used gel hot packs to keep your hands warm?  You may remember breaking a small disk inside the gel, and feeling it get hot to the touch.  Both the cold packs and the hot packs use chemistry to change their temperature! 

When chemical reactions or processes occur, there is always an exchange of energy.  Some of these reactions or processes give off energy as heat; these are called exothermic (‘exo’ meaning outside, ‘thermic’ meaning heat).  Other reactions and processes absorb energy, making the surroundings cooler; these are called endothermic (‘endo’ meaning inside). 

But why are some reactions exothermic while others are endothermic?  Can we predict if a reaction will give off or absorb heat?  As it turns out, we can! 

Chemical Reactions
First, we need to briefly discuss chemical reactions.  A chemical reaction is when one or more chemical compounds are changed into one or more different compounds.  In any chemical reaction, some bonds need to be broken, and others need to be formed—this is how the reaction produces new compounds.  If we know how much energy is required to break the bonds in the reactants (the compounds present before the reaction takes place), and we know how much energy is released on formation of the bonds in the products (the compounds present after the reaction takes place), we can compare them to see how much energy will be produced or consumed by the reaction.  Fortunately for us, there are tables we can use to figure out the energy of the reactants and products. These are called bond energy tables, similar to the one below (1). 

If the formation of the products releases more energy than it took to break the bonds in the reactants, the reaction must give off some of this energy as heat, and so is exothermic.  However, if the formation of the products releases less energy than it took to break the bonds in the reactants, the reaction must take in heat energy from the surroundings, making the reaction endothermic. 

Chemical Processes
The same is true for chemical processes.  A chemical process is what happens when there is a change in the state of one or more chemical compounds (like changing from a liquid to a gas, or dissolving in water), but there is no formation of a new compound.  If we know how much energy the compounds have before they undergo the process (such as melting, or dissolving in water), and how much energy they have after this process, we can discover if the process is endothermic or exothermic.  For example, if we have an ice cube sitting at room temperature, we know the ice cube will begin to melt.  The warmth of the room is melting the ice because the water molecules are absorbing the thermal energy from the air in the room, and this energy is making the molecules move faster and farther away from each other, bringing them from a solid state (ice) to a liquid state (water).  Because this process absorbs energy, it is endothermic.

However, if we put the ice cube back in the freezer, the liquid water will begin to turn back into solid ice.  In this freezing process, the water molecules are giving up thermal energy to their surroundings in the freezer, and are thus losing energy to change states.  This is therefore an exothermic process. 

One type of chemical process that can be either exothermic or endothermic is dissolving of salts in water.  A salt is a compound made up of positively charged ions and negatively charged ions which are held together in a solid state because the positive and negative charges attract one another.  The salt we put on our food is referred to as “table salt”, and is a salt compound made up of sodium ions (Na+) and chloride ions (Cl-). 

If we put salt in water and it fully dissolves (that is, the ions all become evenly dispersed within the water), two exchanges of energy need to happen:

1.       Energy is added to the solution to pull the ions away from each other:  in order to pull the positively and negatively charged ions apart, energy must be added.  This energy needed to pull the ions apart is called the Lattice Energy.

2.       Energy is released into solution when the water molecules surround the ions: as the water molecules are attracted to and surround the ions, energy is released into the solution. This energy released as water molecules surround the ions is called the Hydration Energy.

Whether the dissolving of a salt is exothermic or endothermic depends on which is greater, the Lattice Energy, or the Hydration Energy.  These are usually expressed in units describing the amount of energy released per set amount of salt, such as kilocalories per mole (kcal/mol) or kilojoules per mole (kJ/mol).  We can usually look up the values of the Lattice and Hydration Energy values for a particular salt in tables, such as the one below (2).

For example, if we dissolve table salt in water the Lattice Energy is 779 kJ/mol, and the Hydration Energy is 774 kJ/mol (1).  If we subtract the Hydration Energy from the Lattice Energy, we get a change of +5 kJ/mol:

779 kJ/mol – 774 kJ/mol = +5 kJ/mol

It takes just slightly more energy to separate the ions from one another than is released from the water molecules surrounding the ions.  This means just slightly more energy must be put into the solution than is released back into the solution; therefore dissolving table salt in water is endothermic. 

However, if we dissolve sodium hydroxide (NaOH) in water, it separates into Na+ and OH- ions.  The Lattice Energy for this process is 737 kJ/mol, and the Hydration Energy is 779 kJ/mol.  Subtracting as before, we get a change of -42 kJ/mol.

737 kJ/mol – 779 kJ/mol = -42 kJ/mol

More energy is released into the solution than is required to pull apart the ions; therefore dissolving sodium hydroxide in water is exothermic.  If you dissolve sodium hydroxide in a small amount of water, be careful—the container may get hot enough to burn your hand!

TRY THIS!!

Here’s what you’ll need:

1.       Two small jars or drinking glasses

2.       Two teaspoons

3.       Two cups of distilled water

4.       One half-cup of magnesium sulfate (MgSO4).  You can purchase this online (click here for options).

5.       One half-cup of ammonium chloride (NH4Cl).  You can purchase this online (click here for options).

6.       One thermometer that will measure temperatures from 70-150°F

7.       Safety goggles, one pair for each person participating

8.       Latex or nitrile gloves (you can get these in grocery or hardware stores)

Here’s what you need to do:

NOTE:  Be very careful with the magnesium sulfate and ammonium chloride—they can cause irritation to the skin, lungs and eyes.  Do not breathe them in or get them in your eyes!  You should do this procedure in a well ventilated area, and wear the goggles and gloves to make sure your eyes and skin are protected.

1.       Put on your goggles and gloves!

2.       Pour one cup of distilled water into each of the small jars.

3.       Measure and record the temperature of the water in each jar.

4.       Pour one half cup of the magnesium sulfate into one of the jars.  Stir carefully with a spoon for 20 seconds (don’t worry if not all the magnesium sulfate dissolves).  Measure and record the temperature of the solution.

5.       Pour one half cup of the ammonium chloride into one of the jars.  Stir carefully with a spoon for 20 seconds (don’t worry if not all the magnesium sulfate dissolves).  Measure and record the temperature of the solution.

Did the temperature of the water change each time?  How much did it change?  Did it get hotter or colder?  Are these processes endothermic or exothermic?  Did you observe anything else?  BE SURE TO WRITE EVERYTHING DOWN IN YOUR JOURNAL!


References:

(1)    “Bond Enthalpy/Bond Energy”.  Mr. Kent’s Chemistry Page.  www.kentchemistry.com Accessed 8/28/14.

(2)    “Chapter 13: Solutions”. intro.chem.okstate.edu. Accessed 8/29/14.

A nice cool drink on a hot day is something most of us take for granted.  We also seldom think too much about the ice cream in our freezer or the well preserved food in our refrigerator.  While refrigeration to keep things cool is common today, it was not always.  The first patent for a refrigeration system similar to those we know today was filed in 1856 by James Harrison, an English journalist living in Australia.  Before this, food was preserved with lots of salt, covered in snow during the winter, or simply kept alive on farms and harvested when you needed to eat! 

So how does refrigeration work? 

In general, refrigerators are cooled through the evaporation of a volatile liquid—that is, they use a liquid that evaporates very easily, and this evaporation creates the cooling effect.  They then compress the gas into a liquid again, and the whole process starts over.

Let’s look at this in more detail; refrigerators have basically five parts:

1.       A cooling box, where you put your food

2.       Coils full of liquid

3.       A compressor

4.       Coils full of gas

5.       A valve that separates the liquid-containing coils from the gas-containing coils

The liquid inside many household refrigerators is called HCFC (hydro chloro floro carbon).  This type of liquid has replaced the traditional CFC (chloro floro carbon), which is bad for the environment (www.epa.gov).  The HCFC refrigerant is the liquid (or gas) contained in the coils in the refrigerator, and is what actually cools the box where you store your food.  The refrigerator cycles this HCFC from liquid to gas and back to liquid in the following steps:

1.       Liquid HCFC is contained in the coils on the outside of the refrigerator—the ones that are usually hot.  The liquid inside these coils is at about room temperature. 

2.       This room temperature liquid flows from the liquid-containing coils through a valve into the gas-containing coils. Here the liquid HCFC is allowed to evaporate, which it does very easily since HCFC boils (turns from liquid to gas) at -41.3°F. 

3.       The compressor now pulls in the HCFC gas, and compresses it until it turns back into a liquid.  This makes it hot!

4.       The hot HCFC proceeds back into the liquid containing coils, which allow the heat in the HCFC liquid to dissipate into the surrounding air (which is why the coils feel hot).  Now the HCFC is liquid at room temperature again, and the whole cycle repeats. 

The part of this cycle which cools the refrigerator box (and therefore your food) is step #2, the part where the HCFC evaporates.  In fact, the evaporation of liquid is responsible for cooling many things, including you!

Evaporating liquid is a very efficient way of cooling something.  It’s used in refrigerators, air conditioners, and humans—when you sweat, the water is evaporating off your skin, thus keeping you cool!  What makes this work is something called the enthalpy of vaporization or heat of vaporization, which is the amount of heat a certain liquid needs to go from the liquid phase to the gas phase. 

Picture it like this:  you have a pot of water on the stove, and you want to bring it to a boil.  When water boils, it turns from a liquid to a gas (i.e. steam).  To make water boil you need to increase the amount of heat in the water, so you turn up the burner under the pot.  As the water absorbs more and more heat, it gets hotter and hotter until it reaches 212°F, at which point it becomes steam.  At the point when the water becomes steam, it takes a lot of that heat energy with it into the air and away from the remaining water.  Since the steam removes the heat energy, it cools the water left behind. 

Your body does the same thing when you sweat.  The water in the sweat goes from liquid (sweat) to gas (steam), and as it does so it takes heat energy with it, cooling your body.

The HCFC is like the water in the pot, or like the sweat on your skin, except that it boils (turns to gas) at  -41.3°F instead of 212°F.  This means as soon as it enters the coils inside the refrigerator box, it immediately evaporates, taking heat energy away from the box, cooling the air inside and keeping your food fresh!

TRY AN EXPERIMENT WITH DIFFERENT EVAPORATING LIQUIDS!

Here’s what you’ll need:                  

1.       Two small saucepans, they should be the same size

2.       Two cups plus one tablespoon water

3.       One tablespoon isopropyl alcohol (available at grocery and drug stores)

4.       A stovetop

5.       A non-contact infrared thermometer (this is the kind you can point a laser beam at an object, and it measures the temperature)

6.       Cotton balls (optional)

Here’s what you need to do:

It is pretty simple to demonstrate how evaporation of liquids can cool something.  If you have extra isopropyl alcohol (the kind sold at most drug stores) , soak one cotton ball in water, and another in alcohol.  Rub the water on the back of your left hand, and the alcohol on the back of your right hand.  Your right hand should feel cooler—this is because the alcohol boils at a lower temperature (181°F) than the water (212°F).  This means that the alcohol will evaporate from your skin faster, carrying heat energy with it as it evaporates, making your right hand feel cooler than your left hand (for more information about thermal energy, see our blog about energy transfer).

To see how evaporation of liquids affects temperature, try this:

1.       Pour one cup of water into each of your small saucepans.  Bring them both to a boil, and let them sit at a boil for at least 1 minute.

2.       Remove the pans from the heat, and pour out the water (be careful not to burn yourself with the water or the escaping steam!)

3.       Add one tablespoon of water to one pan, and one tablespoon of alcohol to the other pan.  Swirl the water and alcohol in the pans for 15 seconds, and pour the liquids out again.

4.       Measure the temperature of the bottom of each pan with your infrared thermometer, and write down what you find.

What was the temperature of the saucepan with the tablespoon of water?  What about the saucepan with the tablespoon of alcohol?  Why should these be different?  Be sure to write down all your observations!

To see a hot air balloon in flight is truly something to see!  A typical hot air balloon is 60 feet wide, 80 feet high, contains 77,000 cubic feet of air, and weighs about 800 pounds without passengers (skydrifters.com, sundanceballoons.com)!  So how do these behemoths manage to float so gracefully through the air?

As it turns out, hot air balloons work based on the same principle that causes air currents and wind, thunderstorms, and tornadoes.  They work because hot air rises, while cool air sinks!  If you watch a hot air balloon being filled for flight, you’ll see a large gas burner forcing hot air into the opening at the bottom.  This allows the balloon to fill with air that is hotter than the air surrounding the balloon.  As the air inside the balloon rises in temperature, the balloon rises off the ground!  Have a look at the YouTube video presented below  to watch some hot air balloons being filled for flight (this great video was uploaded to YouTube by Geoffrey McKay--we did not make this video!!).  You’ll notice at the beginning of the video that cool air (the same temperature as the surroundings) is being blown into the balloon with a fan—this fills the balloon with air, but does not cause it to lift.  Only when the balloon is filled by the burners does it lift off the ground.

So why does hot air rise, while cool air sinks?  First, let’s discuss what air really is.  Air is a mixture of different gaseous elements that surround the planet because of gravity (for a more thorough review, see our previous blog, “Can Anything Really be Lighter Than Air?”).  We call this layer Earth’s atmosphere.  The density of this layer of gas—that is, the number of molecules per unit volume—depends on the temperature of the gas.  As the gas heats up, the molecules move faster and faster, and therefore they spread out, making the gas less dense.  As the gas cools down, the molecules slow down and thus get closer together, making the gas denser because there are now more molecules per unit volume. 

This phenomenon is responsible for much of the weather on our planet:  the air closer to the Earth heats up, as the temperature is warmer close to the ground.  This air begins to rise, causing updrafts (you can see these updrafts clearly in the clouds during the summer, when the air near the Earth’s surface is very hot).  These are called thermal columns, because the heated air rises in a column.  As the air gets farther and farther from the Earth’s surface, it begins to cool.  This cooler air then sinks back down to Earth’s surface, and the whole cycle begins again.  This is called atmospheric convection. 

Now that we understand why hot air rises, we can begin to understand why a hot air balloon is able to fly.  The material the balloon is made of is able to keep all that hot air inside the balloon, separated from the cool surrounding air.  This makes the air inside the balloon much less dense than that surrounding it; in effect, the hot air balloon is like a giant bubble of less dense gas!  This is what makes it float up off the ground—it’s just like a bubble of less dense air rising through more dense water! 

TRY FLYING YOUR OWN HOT AIR BALLOON!

Here’s what you’ll need:

1.       One or more ignitable floating lanterns, such as Sky Lantern® (available at www.skylanterns.us, or at your local fireworks outlet)

2.       Matches or a candle lighter

3.       A fire extinguisher...just in case!

NOTE:  Be sure to do this on a calm day!  Wind will interfere, and will increase the risk of starting a fire.  Also be sure that your area does not have burning restrictions!

Here’s what you need to do:

In general, just follow the instructions on the lantern’s packaging!  You will light the fuel below the large paper lantern using your matches or lighter, being careful not to burn the lantern.  Allow the lantern to fill with hot air, let it go, and watch it fly!

CHALLENGE:

Now that you’ve seen a paper lantern fly, try to make your own!  Use light tissue paper, some strong glue, and some very thin wire for the base.  Use old newspaper soaked in vegetable oil for the fuel.  Try your lantern in an open area, far away from any homes! 

If you make a paper flying lantern, take pictures or video, and share with us!  Go to https://www.facebook.com/discoveryexpresskids, and post them on our page!!

When you are outside in the summertime, and you go into your house, you probably feel cooler once you are inside.  However, when you are outside in winter you probably feel warmer once you are inside the house (provided you live in a place where it is cold in winter!).  Yet the house is probably always about the same temperature.  Why does it feel warm in winter and cool in summer?

This difference in the way you feel in the house, despite that it is always the same temperature, comes from differences in thermal energy between you and the house.  Thermal energy is that portion of the energy in any body or object that is responsible for its temperature, according to Robert F. Speyer in his Thermal Analysis of Materials.  (In general, energy is just a property of any object or system that can be transferred to another object or system through some interaction.) Therefore, if one object has a higher temperature than another object, this object has more thermal energy. 

Like all forms of energy, thermal energy likes to transfer from an area of higher energy to an area of lower energy, until both areas are equal.  This means that if our boxes above touch, the one with more thermal energy will transfer some of that energy to the other box, until they both have the same amount of energy—that is, until they are at the same temperature.

The same sort of transfer happens between you and the air inside your house.  In winter, because your house has a heating system that is set by the thermostat, the air inside your house is kept warm, say 70°F.  Outside the air is much colder; say around 20°F depending on where you are.  If you are outside, and you enter your house, thermal energy is transferred to you from the air in the house, since you have less thermal energy than the air does. 

In the summer the opposite happens:  you come indoors, and you have more thermal energy on your skin than the air in the house does.  This means some of the thermal energy on your skin will transfer to the air in the house, until your skin and the air in the house are the same temperature. 

This transfer of thermal energy from some other object to you or from you to the other object is responsible for the feeling of warm or cold.  When you touch something that is warmer than you—that is, it has more thermal energy and is therefore at a higher temperature—the flow of energy from the object to you gives you the feeling of becoming warmer.  If you touch an object that is cooler than you, some of the thermal energy in your skin is flowing out and into the other object.  This is why your house at the same temperature can feel warm or cool depending on the time of the year—it all depends on who or what is transferring  thermal energy!

TRY IT!

Here’s what you’ll need:

1.       A large bowl of very warm water, but not hot enough to burn you, about 90°F (like a hot bath)

2.       A large bowl of ice water

3.       A large bowl of water at room temperature

4.       A watch with a sweep second hand, or a stopwatch

Here’s what you need to do:

1.       Place all the bowls of water on a table or counter, ice water and hot water on either side of you, and the room temperature water in front of you.

2.       Place one hand in the hot water, and your other hand in the ice water.

3.       Leave your hands this way for at least 30 seconds, or 60 if you can.

4.       After 30 seconds, pull both hands out of their respective bowls, and place them both in the room temperature water.

What are your hands feeling?  Is there any difference?  Why is that?  Be sure to write down what you feel and observe!

Speyer, R. F. (2012). Thermal Analysis of Materials. Materials Engineering. Marcel Dekker, Inc., New York, New York.

Today if you find you are lost, you can usually just pull out your GPS (Global Positioning System) to find out exactly where you are, and find exactly where you want to go.  Many cars and nearly every cellular phone have GPS units or apps to use for finding your way.  But the GPS system didn’t become fully operational until 1995.  People have needed to find their way for hundreds of years!  What did people do before GPS to find where they were going?

Throughout the years humans have used a number of methods to find their way (that is, to navigate) to their intended destination x.  Hundreds of years ago people would use known landmarks, or the position of the sun, moon, and stars to decipher where they were.  Beginning about the year 1040 AD, the Chinese began using the compass for navigation1.  A compass (in this case, a magnetic compass) is simply a small magnetized needle or bar which is balanced on a point on which it can easily pivot or spin.  This magnetized needle will pivot on this point such that one end of the needle points toward North.  Generally this end of the needle is painted red, or otherwise indicates to the user which way is North.  Using this simple device, human beings of the ancient world were able to cross oceans and continents, and .find their way home again.

Why does Earth have a magnetic field surrounding it?  Recall that magnetic fields are created by the movement of charged particles (see our most recent blog about magnets and magnetism).  Scientists believe that Earth’s magnetic field is created by the movement of hot liquid and crystallized iron at its core2.  As the Earth revolves on its axis, the molten iron at the core—and thus the electrons in the iron—are also rotating.  These rotating electrons are what create the magnetic field.

TRY MAKING YOUR OWN COMPASS!

Here’s what you’ll need:

1.       A needle or other thin, lightweight piece of steel

2.       A Styrofoam cup

3.       A scissors

4.       A glass pie plate

5.       A strong bar magnet (good ones are available from eBay and Amazon.com, but you can always try your local hardware store)

Here’s what to do:

1.       Fill the pie plate with water from your kitchen sink.  Place the plate on a flat surface.

2.       Carefully cut the bottom off the Styrofoam cup using your scissors.  Be sure not to leave any of the cup edges.

3.        Magnetize your needle:  take the strong bar magnet and rub one end of it along the needle in only one direction at least 20 times.  This will align the atoms in the needle, causing it to become magnetized.  You can check to make sure your needle is magnetized using a few paper clips; if the needle will pick up the paper clips, it’s magnetized!

4.       Carefully place this needle on top of the disc of Styrofoam you cut from the cup earlier.  Float the Styrofoam with the needle in the pie plate of water.  The needle will slowly turn to point North!
What did you observe?  Did your needle point North?  Did it stay this way?  Be sure to write down all your observations!

CHALLENGE YOUR FRIENDS TO A TREASURE HUNT!

Hide a flag in a tree or in some tall grass.  Make up a map to the object telling your friends how many feet or steps North, South, East, or West they should go from where they start.  Then provide them with all the things they need to make their own compass to figure out which way is North!  This works when the area is not very familiar, so going to a State Park or wooded campground would likely be a good location.

References for further reading:

1.            Lowrie, W., Fundamentals of Geophysics. 2nd ed.; Cambridge University Press: Cambridge; New York, 2007.

2.            Brain, Marshall.  "How Compasses Work"  01 April 2000.  HowStuffWorks.com. <http://adventure.howstuffworks.com/outdoor-activities/hiking/compass.htm>  28 May 2014.