Today we are going to learn more about simple machines. Last week we focused on the lever. You learned about levers by creating a ping-pong ball launcher and testing different kinds and positions of fulcrums.
If you missed it, check it out here: http://www.discoveryexpresskids.com/blog/levers-and-launchers
Reminder, a lever is: A simple machine that contains a beam and a fulcrum.
A fulcrum is: The point at which the beam of the lever rests and pivots.
Examples: A seesaw, scissors, chopsticks. Can you think of more?
This week, we are going to test out an inclined plane. Before we learn about inclined planes, let’s review what a simple machine is.
A machine is...
-something that makes work easier for us.
Work can be defined as...
-the force acting on an object in the direction of motion.
-force times distance. (Work = Force x Distance)
Work sometimes is too great for humans to complete on their own, so we use machines to help us with that work.
A simple machine could be any of the following:
- Wheel and axle
- Inclined plane
Read more about the six simple machines that make work easier at http://www.livescience.com/49106-simple-machines.html.
Check out this video for a quick explanation of what an inclined plane does for us:
1. What is another word for an inclined plane?
2. How does an inclined plane make work easier for us?
3. When would an inclined plane be useful?
4. What is mechanical advantage?
Can you think of an inclined plane that you’ve seen in real life? Here’s a few examples:
YOU WILL NEED:
- Strong rubber band
- Bag of rice or sand
- Plank of wood or cardboard
- Stack of books
- Measuring tape
Here’s what to do!
- Fill a plastic bag with rice or sand. This is your load.
- Cut a rubber band and tie it around the bag. Pick up the load with just the rubber band to make sure the band holds. What happens to the rubber band? You should see it stretch under the weight of the load.
- Set up a stack of books. Measure how tall the books are. Record the height.
- Lift the load to the top of the stack of books using only the rubber band. Measure how far the rubber band stretched at the point where the load reaches the top of the books. Record your measurement.
- Now, you are going to create an inclined plane. Place a plank of wood or cardboard leading from the floor to the top of the stack of books. It should look like a ramp. Take a look at the image below. Measure how long the ramp is. Record the length.
7. You should have noticed that the rubber band stretched more without the inclined plane. When you added a simple machine, the work became easier and the rubber band stretched less.
8. Now, you’re going to calculate the mechanical advantage. Remember the end of that video? Mechanical advantage is how much the simple machine helped you. The formula to finding mechanical advantage for an inclined plane is slope / height. Take a look at the image below for reference:
When you used the inclined plane, you did have mechanical advantage. Let’s say the ramp is 18 inches long.
Mechanical advantage = slope / height
Mechanical advantage = 18 / 9
Mechanical advantage = 2
9. What happens when you make the inclined plane shorter and steeper? Repeat steps 5 and 6 to test it out. What happens when you make the inclined plane longer and less steep? Repeat steps 5 and 6 to test it out. Did the rubber band stretch more when the inclined plane was steeper or less steep? What does that tell you?
10. Calculate mechanical advantage for both inclined planes. Is mechanical advantage higher or lower when the inclined plane is steeper?