KE and PE in Pendulum.docx

KE and PE using the Pendulum Lab Objective – to develop a visual concept of the relationship between KE and PE during an object’s motion. Main Link: https://phet.colorado.edu/en/simulation/pendulum-lab PART I : Go to the PHET Pendulum lab and select “Lab”. If you have never used this application before you might want to play around with the “Intro” and “Energy” screens first. On the right, leave Length, Mass, Gravity and Friction alone for now. At the bottom left, turn on the ruler and the timer . At the top left, turn on the Energy Graph . Play with the pendulum and watch how the KE and PE bars change. Change the starting angle, mass and length of string. One at a time to see how it affects different aspects of the energies and period. You might want to change the speed (lower center) to “Slow”. • Make a preliminary statement that describes how these two bars are related to each other and how these relationships change as the pendulum moves through its cycle. The bars are related because they are both energies. They change depending on the location of the pendulum. So I the can is in motion, there will be kinetic energy, however if it is still and not moving, there will be potential energy. PART II: PE and KE At the lower center, turn the speed to “Slow”. At the left, drag the ruler to the KE/PE bar graph. Swing the pendulum so the total Energy Shows. Place the ruler so that 5 cm is above the total energy bar. At this point the total should be 55 cm - 5 cm = 50 cm. Remember to subtract that 5 cm each time you take a reading. (Note: this needs to be altered depending upon the length of your energies as you continue through the lab.) Turn on the velocity. Starting at 90° ( as the pendulum swings), collect data on the height of both KE and PE bars at various locations: Location Of Pendulum Bob Kinetic Energy (cm) Potential Energy (cm) Questions: Farthest Right 30 cm 30 cm 2. At what point is the PE the greatest? At the start of the simulation at 90 degrees Bottom Dead Center 0 cm 0 cm 3. At what point is the KE the greatest? There is no kinetic energy because the bob does not move at the center. Farthest Left 30.5 cm 30.5 cm 4. At what points is V (velocity) the highest? Just before the bob passes the dotted line.

Halfway Left 9 cm 9 cm 5. What is the relationship between KE and V? They are equal. PART III: Length vs Period 6. Hypothesis: How would increasing the length affect the period? I think that if you increase the length of the wire, it will take longer for the can swing to and back. Length Of Pendulum String Period .1 m 0.7448s .3 m 1.2969s .5 m 1.6811s .8 m 2.1179s Questions: 7. What happened to the period as the length of the bob increased? As the length increases, the period took longer to finish. PART IV: Mass vs PE,KE, and total Energy 12. Hypothesis: How would increasing the mass affect the PE, KE and total energy of the system? I think by increasing the mass of the can, the PE and KE would be a lot more because of the weight. Hit reset and click energy graph, ruler and timer. Mass of Pendulum Bob Period (secs) Kinetic Energy (cm) At bottom Kinetic Energy (cm) At top Potential Energy(cm) At Bottom Potential Energy(cm) At Top Total Energy (cm) .15 grams 1.9811 s 6cm 0cm 0cm 6cm 6cm

19. How does the change in mass affect the period? The change in mass does not affect the period at all. 20. Switch to the moon. How does the change in gravity affect the period? Since there is almost no gravity on the moon, the period will take much longer to complete. Also, the pendulum goes all the way to the top without much energy.