Jump! An elastic potential to kinetic energy investigation. Also known as “Can Paper Frogs Do Work?

Elastic Potential Energy Elastic potential energy can be created when a spring (or a rubber band) is either stretched or compressed. Basically, you change the shape of an object (you do work on the object) to deform it. As long as you hold the object in its deformed shape, it will have the potential to do work – in other words, if you let go it will move and release the energy you put into it.

Energy (calculated) = Work (calculated) Energy is defined as the ability to do work or cause the change in the speed, direction, shape, or temperature of an object. Work is done when a force causes an object to move. There is a very close relationship between work and energy. Both work and energy are measured in Joules.

Huh? OK, check out Mrs. D - holding a large rubber band. The rubber band is stretched – it’s shape is changed. If she suddenly let go of the rubber band it would go into motion – it would have Kinetic energy… …and we already know objects with kinetic energy can do work.

Jumping Frogs Make a jumping frog the way it is shown in the video and outlined in the handout. How does the frog move? Why does it move? Is this compression or stretching? Try different angles and different amounts of pressure to see if you can control the way the frog jumps. Try to measure how much you press down on the back legs, how does that affect how high or how far the frog jumps?

Make observations Label the next page in your lab notebook Elastic Potential Energy Conversions. Draw a diagram of your frog and explain, briefly, how you made it. Make observations about the way the frog responds in your lab notebook. Think about what you learned as you “played” with your frog. Practice controlling your frog’s motion until you can predict where it will jump.

Jumping Frog Energy 1. Where does the energy come from to move your frog? 2. Can the amount of energy your frog has be changed to make it jump at different heights and distances? Explain. 3. When does your frog have potential energy? 4. When does your frog have kinetic energy? 5. When does your frog have the most energy? Explain your answer. 6. When does your frog have least energy?

Working Frogs Remember, whenever an object has energy it has the ability to do work. The kinetic energy in your frog as it moves can be transferred to a small weight, for example, a washer.

How much work can a jumping frog do? Measure the mass of the washer given to you by the teacher. Multiply the mass in kg by the gravitational constant to determine the force of the washer’s mass. Record the force in newtons in your lab notebook.

Push it… Suspend your washer on a string where your frog can jump up and push it. Design a way to reliably measure the distance the push moves the washer.

Draw a diagram of your work measuring setup in your lab notebook.

Go the distance Record the distance data for each successful “working jump” Figure out the average distance your frog moved the washer and record it in centimeters. Convert that average distance into meters (the standard unit must be used in the next part of the lab)

Calculations time! Calculate the amount of work your frog did by multiplying the force of the washer’s mass by the average distance the washer moved. Work (Joules) = Force (Newtons) x distance (meters)

Estimate the energy… Now, you know the energy your frog had stored in it when you compressed the back legs (minus some for error, air resistance and a little loss to sound). So - who’s frog has the most powerful kick?