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Thermal Conduction

6/22/2017

Have you ever gone to a playground and slid down a metal slide, only for it to burn your skin a little bit where you touch the metal? If you compared the heat of two slides, one metal and the other plastic, you would find the metal slide to be much hotter to touch. This is because of thermal conduction. In the summer heat, metal feels hotter than wood or plastic because its ability to conduct heat is so much better.

There are many examples of heat conducting objects in the household: a traditional oven will heat a metal coil on the bottom of the oven, which heats the air inside by way of conduction (and convection when a fan is used). On a larger scale, we know that the heat source for our planet is the sun. Energy from the sun is transferred through space and through the earth's atmosphere to the earth's surface. Since this energy warms the earth's surface and atmosphere, some of it is transformed into heat energy.

Conduction is the transfer of heat energy from one substance to another, or within a substance. Have you ever left a metal spoon in a pot of soup being heated on a stove? After a short time the handle of the spoon will become hot. This is due to transfer of heat energy from molecule to molecule or from atom to atom. We also observe this when objects are welded together; the metal becomes hot (the orange-red glow) by the transfer of heat from an arc. This is a very effective method of heat transfer in metals!

Convection is similar to conduction, except instead of transferring heat between objects, convection is the transfer of heat energy through fluids. This type of heating is most commonly seen in the kitchen when you see liquid boiling.

Air in the atmosphere acts as a fluid. The sun's radiation strikes a surface, thus warming it. As the surface's temperature rises due to conduction, heat energy is released into the atmosphere, forming a bubble of air which is warmer than the surrounding air. This is why you can feel how warm an object is by holding your hand just barely above it.

Test it at Home!

You can find out the thermal conductivity of different materials relatively easily at home! You’ll only need a few objects that have a flat/smooth surface. Try these for starters:

A piece of metal
A piece of wood
A plastic plate
A styrofoam plate

Place all of your materials out in the sun for about 10-15 minutes. Make sure it isn’t too windy so nothing blows away! Next, you’ll need to grab as many ice cubes as there are different materials. If you have a scale, you should measure the masses of the ice cubes to make sure they all have relatively the same mass.

Before the ice melts too much, place an ice cube on each of the materials that have been sitting in the sun. Use a timer and watch the ice to see which of the cubes melts the fastest. The material that has the ice that melts first will be the material with the highest thermal conductivity. The material with the lowest conductivity will have ice that is the last to melt! Did you expect these results? What do you think could be used in another experiment to test the conductivity of different materials?

References:

“The Transfer of Heat Energy”. National Weather Service, National Oceanic and Atmospheric Administration.

Image Credits:

Gruhl, Teodoro. “Slide”. Released into the public domain. Uploaded on 6/20/17 from publicdomainpictures.net

Seoane, Xoan. “Cooking on a Low Heat”. Released into the public domain. Uploaded on 6/20/17 from publicdomainpictures.net

“Ice Cubes for Beverages”. Released into the public domain. Uploaded on 6/20/17 from commons.wikimedia.org

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Metamorphosis: Butterflies and Frogs

6/14/2017

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The heat of summer brings out all kinds of different creatures, mostly insects. Monarch butterflies are one of the most common indicators that summer has arrived in North America. However, they don’t look like butterflies when they hatch! The life cycle of a moth or butterfly is a process called complete metamorphosis. That means that they have four distinct stages: egg, larva (caterpillar), pupa (chrysalis), and adult. For monarch butterflies, it takes about a month to grow from an egg to an adult.

What is Metamorphosis?

People can refer to many different kinds of changes as metamorphoses, like drastic makeovers, for instance. But in science, the term 'metamorphosis' refers to a change that an animal goes through as it grows older. The change has to be significant (that is, it has to be really big!)--the final life stage bears no resemblance to the others. For example, humans don’t go through metamorphosis because babies have the same physical structures and functions as an adult would.

Many amphibians also go through metamorphosis. They start their lives in the water with gills and a tail to swim around with. As they get older, the lungs form to replace the gills and legs start to develop so they can walk (or hop) on land. For frogs and toads, the tail gradually shortens until it is nonexistent.

Metamorphosis is caused by hormones being released into the organism’s body. Similar to traffic signals, hormones tell the body when to start growing or producing something, and when to stop! An insect’s growth/metamorphosis is controlled by hormones that are synthesized by endocrine glands near the front of the body. Metamorphosis in amphibians is regulated by the concentration of thyroxine (a hormone produced in the animal’s thyroid gland) in the blood, which stimulates metamorphosis, and prolactin (produced in the pituitary gland), which counteracts the other hormone’s effect and stops metamorphosis.

Life Cycle of a Butterfly

An adult female butterfly will often lay her eggs on the underside of a leaf to protect them from predators. There, the unfertilized eggs wait for a male butterfly to fertilize them so they can begin to form and hatch as larva. The word larva refers to the growth stage of all insects with complete metamorphosis; caterpillar refers only to a butterfly or moth in this stage.

Caterpillars have three distinct body parts: head, thorax, and abdomen. As the caterpillar grows and becomes too large for its skin, it molts, or sheds its skin. Just before they pupate, caterpillars spin a silk mat from which they hang upside down. The silk comes from the spinneret on the bottom of the head. As it sheds its skin for the last time, the caterpillar stabs a stem into the silk pad to hang.

Many moth caterpillars (but not all) spin a silken cocoon to protect them as they grow into an adult moth. Butterflies don’t do this, and their pupa stage is often called a chrysalis to differentiate between moths and butterfly pupae. After approximately 10 to 14 days as a chrysalis, the butterfly is ready to emerge.

When it emerges from its chrysalis, its wings are small and wet, and the butterfly can’t fly yet. It has to pump fluids from its abdomen through the veins in its wings to stimulate the wings to expand to their full size. Next, the wings dry and the butterfly must exercise flight muscles before it can fly. After a couple of days, the butterfly is ready to mate and the cycle begins again!

Watch it in Real Time!

To witness metamorphosis yourself, it’s fairly easy find kits that allow you to “grow” your own frog or butterfly from a tadpole or caterpillar! We think the TADventures kit from Grow-A-Frog* is a good choice, although there are others. The Grow-A-Frog kit contains a translucent tadpole ready to grow into a frog, a habitat, food for both tadpole and froglet, soil, and a fun fact booklet. When the frog is a fully-grown adult, it prefers to stay in the water, so you won’t need to transfer your frog to a terrarium.

If butterflies interest you more than frogs, there’s also the Butterfly Garden from Insect Lore*. This kit comes with a pop-up mesh habitat, live caterpillars in a cup, and a feeding pipette. The caterpillars already have the food they need in the cup, so they won’t need anything from you until they hang upside down from the top to form chrysalides. Once they have hardened, you can gently remove the top of the cup and place it in the mesh habitat. After about a week, the Painted Lady butterflies will emerge.

*Grow-A-Frog, Insect Lore and their associated companies are in no way affiliated with Discovery Express Kids. Recommendations made on this page are unsolicited, and represent popular choices by our teachers.

Image Credits:

Williams, Laurie. “Butterfly Life Cycle”. Released into the public domain. Uploaded on 6/13/17 from publicdomainpictures.net

“Rana Temporaria Spawn”. Released into the public domain under the Creative Commons Attribution Share-Alike 3.0 License. Uploaded on 6/13/17 from commons.wikimedia.org

Pinckard, Christina. “Caterpillar on Leaf”. Released into the public domain. Uploaded on 6/13/17 from publicdomainpictures.net

McCarty, Megan. “Enclosing Monarch”. Released into the public domain. Uploaded on 6/13/17 from commons.wikimedia.org

Black, Keli. “Exploring”. Released into the public domain. Uploaded on 6/13/17 from pixabay.com

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Hearts and Homemade Stethoscopes

6/8/2017

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The heart is one of your most important organs. It pumps your blood all throughout your body, and allows blood vessels to transport oxygen to other organs. The heart is also the hardest-working organ in the body - it keeps pumping at all times and only ever gets a bit of a break when you’re relaxing or sleeping! Every minute, your heart pumps about five quarts of blood through a system of blood vessels that's over 60,000 miles long, which is equivalent to about 2,000 gallons of blood every day!

How the Heart Works

The human heart has four distinct components: the left atrium, the left ventricle, the right atrium, and the right ventricle. The right side of your heart receives blood from the body and pumps it to the lungs. The left side of the heart does the exact opposite; it receives blood from the lungs and pumps it out to the body.

Oxygenated blood from your lungs enters the left atrium and is pumped down into the left ventricle to be sent out to the rest of your body. Once the oxygen has been delivered to the other organs and tissues, veins transport the blood back to the heart through the right atrium. Another heartbeat and that blood is pumped into the right ventricle and out to the lungs to receive more oxygen. All of this happens in the span of only a few seconds!

Before every heartbeat, the heart fills with blood and its muscle contracts to squeeze out the blood with enough pressure to push it through the arteries. Your heart is about the size of your fist, so you can try making a loose fist and then squeezing as hard as possible - that’s how your heart beats inside your chest!

The Importance of a Healthy Heart

Many different factors affect your heart’s health, that’s why it’s so necessary to adopt a healthy lifestyle! If your heart isn’t healthy, there is a good chance that your other organs are unhealthy as well.

The greatest risk factor for heart disease is directly related to a person’s activity level. Living a sedentary lifestyle (spending more time sitting or lying down than being active) almost doubles your risk of heart disease or failure.

That’s why the American Heart Association recommends logging 150 minutes of moderate exercise every week to keep your heart healthy. Other ways to lower heart disease risk include not smoking, controlling cholesterol, eating better, managing blood pressure, maintaining a healthy weight, and reducing blood sugar.

A person’s heartbeat can reveal a lot about their cardiovascular fitness, which is extremely important to good health. When a person is in good cardiovascular condition (that is, their heart and lungs are in good condition), the volume of blood their heart is able to pump with each beat increases, and so does the amount of blood in their body. Every time their heart beats, more blood is carried to their muscles, bringing oxygen and nutrients and carrying away waste more efficiently. This means that their heart will have to beat more slowly when they are at rest, and that it will return to resting rate more quickly after exercise, because they can supply their bodies with oxygen and nutrients (and get it to return to normal) with fewer beats per minute.

Think of a person’s body as a city, and their cardiovascular system as the streets and highways carrying people around to all the organs and tissues. If a person is in good cardiovascular condition, their city streets and highways are wider and well maintained, and so more cars can get where they need to go faster. If they are in poor cardiovascular condition however, the streets and highways are narrow, and can carry fewer cars at one time.

Stethoscopes

One of the ways a doctor checks heart health is by listening to a patient’s chest using a stethoscope. A stethoscope is made of solid, yet flexible, materials that transmit the sound of a heartbeat more efficiently than trying to put their ear to a patient’s chest. This way is much less invasive! When listening to a patient’s heart, they are checking for the normal ‘lub-dub’ sound it makes as it contracts to pump blood. Any irregular patterns or sounds (like a ‘whoosh’) might indicate a problem that should be investigated.

Make a Simple Stethoscope at Home!

If you want to be able to listen to your heartbeat without going to the doctor, it’s relatively easy to make a stethoscope at home that will help you hear what’s going on inside your chest. Here’s what you’ll need:

Small plastic funnel, about 3 inches (7.5 cm) wide at the mouth
Plastic tubing, sized to fit over the thin end of the funnel, 1 foot (30.5 cm) segment
Plastic wrap, 1 4-inch (10 cm) square
Duct tape or rubber bands
Stopwatch
Scissors
Paper and pencils

First, you need to push one end of the funnel into the plastic tube.

Next, stretch a piece of plastic wrap over the funnel (tightly!).

Finally, secure it in place with a strip of duct tape or rubber band (the rubber band is shown here).

Now you should be able to place the funnel on your chest, place the other end of the tube carefully in your ear, and listen to your heart! You can also try listening to your lungs by taking deep breaths. You can even listen through walls with your stethoscope! Try it, see if you can hear things like plumbing, footsteps, or voices!

You can use this stethoscope to measure your fitness level by counting the number of times your heart beats in a minute. First, measure your standing heart rate by standing upright for 2 minutes. Be sure to stay still! With your new stethoscope, listen carefully to your heartbeat. Count the number of times you feel your heartbeat in 15 seconds.

Using your watch or stopwatch, time this precisely and write down the number of beats you hear. Multiply this number by four to get the number of beats per minute! Find the number of beats per minute in the table below, and record how many points you earned. Be sure to write this down!

Next, measure your resting heart rate by lying down on the floor for two minutes before checking your heart rate. Record your resting heart rate as you did for your standing heart rate by repeating the steps above. Find the number of beats per minute in the second table below, and record how many points you earned. Be sure to write this down as well!

Finally, measure your heart rate just after exercise, and how long it takes to return to normal.
Start by jogging in place for 10 seconds and time this with your watch or stopwatch. As soon as you stop, immediately begin recording how many times you feel your heartbeat in 15 seconds and write this number down.

Continue recording how many times your heart beats every 15 seconds until the number is the same as when you took your standing heart rate. Write each number down. Now, count how many numbers you had to write down, and divide that number by four. This is how many minutes it took for your heart rate to return to the normal standing rate.

Multiply the first number you wrote down immediately after exercise by 4 to get beats per minute. Make sure to write this down too! Find the number of minutes it took for your heart rate to return to normal in the third table below, and record how many points you earned. Be sure to write this down! If it took longer than 2 minutes, give yourself 6 points.

Subtract your standing heart rate from your heart rate just after exercise. This is how much your heart rate increased after exercise. Finally, in the fourth table below, find your standing heart rate on the left, and use the heart rate increase after exercise value on the top to find your points. Write this down!

Add up all the points you earned. Use the scale below to determine your level of fitness.

References:

“Your Heart and Blood Vessels”. Cleveland Clinic Health Library. Accessed on 6/1/17.

Image Credits:

Hudson, Dawn. “Re-Digitized Human Heart”. Released into the public domain. Uploaded on 6/2/17 from publicdomainpictures.net

Capac, Manco. “Atrial Septal Defect”. Released into the public domain. Uploaded on 6/2/17 from commons.wikimedia.org

Oberholster, Venita. “Healthy Diet Educational Poster”. Released into the public domain. Uploaded on 6/2/17 from publicdomainpictures.net

Nyren, Erin (2014). “Cardiovascular Fitness, Explained With Cars”. Science Projects for Grades 7 and 8. Discovery Express Kids, LLC, Fargo, ND.

Hodan, George. “Stethoscope”. Released into the public domain. Uploaded on 6/2/17 from publicdomainpictures.net

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Thermal Conduction

Metamorphosis: Butterflies and Frogs

Hearts and Homemade Stethoscopes

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