ENERGY: KINETIC VS. POTENTIAL
Have you ever thought about.....why you are able to get out of bed in the morning and come to school? Why the alarm clock sounds in the morning? How the toaster toasts bread? How your car runs? How you run? Why your nose runs? How your computer runs? How everything runs? NO, you say? WHY NOT?????? Do you not have enough energy? Funny, I said energy, because that is the answer to all of the questions from above. Everything runs because of energy. In other words, energy is the stuff that makes stuff do stuff!!!!!! Or in proper scientific talk: the ability to do work or cause change. In this investigation, you will examine and analyze objects at rest and in motion in order to describe the relationships that exist between the two types of stuff that make stuff do stuff (energy).
Objective
When you have completed this investigation, you should be able to analyze the movement of a pendulum in order to describe the relationship between potential energy and kinetic energy in moving objects.
Materials
pendulum
Activity 1:
1. Observe the pendulum that your teacher has set up in front of the class.
2. Label the parts of the pendulum. Fixed point
String, bar, or rod
Pendulum bob
3. Name the two types of energy displayed by the pendulum.
Kinetic energy
Potential energy
4. Observe the diagram in Figure 1.
5. Circle which position(s) you believe have the greatest potential energy.
6. Place a box around the position(s) you believe have the greatest kinetic energy.
7. Read the selection below.
8. Use the information in the reading selection to evaluate your predictions from tasks 4 and 5.
My prediction was…______right. I thought that ______
The correct answer was….______
Activity 2
9. Explore the following web page: http://www.walter-fendt.de/ph14e/pendulum.htm Be sure to select the energy applet from the right hand side.
10. Describe the energy conversion that takes place in a pendulum.
As the pendulum falls, the potential energy turns into kinetic energy, because it gains velocity and loses height. As the pendulum rises, the kinetic energy turns into potential energy, because it gains height and loses velocity.
11. Look at the pendulum below, and label the places where it has the maximum and minimum potential energy and kinetic energy.
max pot. max pot.
min kin. min kin.
max kin.
min pot.
Activity 3:
12. Observe the movement of the pendulum in the teacher demonstration.
13. Describe the energy conversions of the pendulum from the time the pendulum starts to the point when the pendulum stops.
When the pendulum starts, it has all potential energy. As it falls, the potential energy is transformed into kinetic energy. At the bottom, the energy is all kinetic. As the pendulum rose the kinetic energy is transformed back into potential energy. When the pendulum stops, all of the energy is again potential energy.
14. What do you think causes the pendulum to eventually stop?
The pendulum eventually stops due to friction from the air and at the point where the string is connected.
Law of Conservation of Energy E.C.
Energy may not be created nor destroyed. It may only be transformed from one form to another.
Analysis (The Great Ball Drop)
1. Observe the diagram and caption.
2. Label the points of maximum and minimum potential energy and kinetic energy on the diagram.
3. Explain the error(s) in Stanley's thinking using information from today's investigation. Be sure to mention points of maximum and minimum potential and kinetic energy. Address BOTH of Stanley’s claims.
______
4. Not all of the potential energy that exists at the top is directly converted to the kinetic energy of the rolling ball. Determine what happens to this "lost" energy. (HINT: Think about friction and the law of conservation of energy).
______
______
EEM - 25