Physical Science II Name: Brian NguyenEnergy Skate Park - Conservation of Energy Hour: 6 Date: 9-28-12

Energy Skate Park Simulation - Conservation of Energy

Purpose: When Tony Hawk wants to launch himself as high as possible off the half-pipe, how does he achieve this? The skate park is an excellent example of the conservation of energy. The law of conservation of energy tells us that we can never create or destroy energy, but we can change its form.

In this lab, you will analyze energy transfer between gravitational potential energy, kinetic energy, and energy lost due to collisions or friction (thermal energy) as a skate boarder rides along a track.

Instructions: Go to the web address written below, and click the “Run Now” button ( ). The simulation will open in a moment.

http://phet.colorado.edu/en/simulation/energy-skate-park-basics

Take some time to play with the simulation. Turn on the ‘Bar Graph,’ ‘Grid,’ and ‘Speed’ options on the right side of the screen. Become familiar with the ‘Reset’ buttons on the right and how to change the speed of the simulation with the buttons on the bottom.

Part I: Introduction (Turn on the ‘Bar Graph,’ ‘Grid,’ and ‘Speed’ options.)Set the skater 2 meters above the ground on the ramp and release him.

1. What type of energy does the skater have at the 2 meter mark?The skater at the 2 meter mark has potential gravitational energy.2. How high does the skater get on the other end of the ramp?The skater gets to the 2 meter mark on the other end of the ramp.3. Explain, in terms of the conservation of energy, why the skater will never go higher than your answer

to question 2 at this point.In terms of the conservation of energy, the skater will never go higher than my answer to question 2

because the amount of energy the skater has available to be converted to kinetic movement energy isn’t being converted to another type of energy, because of Newton’s 3rd Law. When the skater goes

down the ramp, the potential gravitational energy is converted to kinetic movement energy. The skater’s energy isn’t lost from any other forces that may convert the energy to another form of energy in this simulation. The amount of force the skater has is dependent on the speed the skater travels; therefore, the more kinetic movement energy, the more force the skater will deal. The skater dealt a force of “2 meters” when he just reaches the bottom of the ramp and will rebound to the 2 meter mark at the other side of the ramp. According to Newton’s 3rd Law, when an object collides in another object, the force of the object is applied to another object, and the same amount of force is rebounded back into the object. Therefore, if the skater dealt a force of “2 meters”, then the skater will travel to the 2 meter mark.

Hit the ‘Reset All’ button.

4. If you were to place the skater at the 5 meter mark, how high will the skater go on the other side of the track? Try it to confirm your prediction.

If I were to place the skater at the 5 meter mark, then the skater will travel to the 5 meter mark of the track because the skater will exert enough force when he is at the bottom of the ramp that the skater travels to the 5 meter mark on the other side of the ramp. Because there is no friction occurring, the energy is not lost when the skater travels and the skater is able to rebound to the other side of the ramp with the same amount of force as when he came down the ramp.

5. How does the skater’s kinetic energy change as he moves down the ramp?The skater’s kinetic energy increases as he moves down the ramp because the gravity exerts a force that makes the skater fall down and convert the skater’s potential gravitational energy into kinetic movement energy._____________________________________________________________________________________

6. How does the skater’s kinetic energy change as he moves up the ramp?The skater’s kinetic energy decreases and changes to potential gravitational energy because the gravity of the earth will exert a force that slows down the skater by turning his kinetic movement energy to potential gravitational energy. _____________________________________________________________________________________

7. How does the skater’s potential energy change as he moves down the ramp?The skater’s potential energy decreases and changes to kinetic movement energy. Gravity exerts a force on the skater, which converts his potential energy to kinetic movement energy. _____________________________________________________________________________________

8. How does the skater’s potential energy change as he moves up the ramp?

The skater’s potential energy is increasing he moves up the ramp because gravity is exerting a force on the skater, which makes the kinetic movement energy to convert into potential gravitational energy as the skater moves up the ramp. _____________________________________________________________________________________

9. How does the skater’s total energy change as he moves down the ramp?The skater’s total energy doesn’t change as he moves down the ramp._____________________________________________________________________________________

10. How does the skater’s total energy change as he moves up the ramp?

The skater’s total energy doesn’t change as he moves up the ramp._____________________________________________________________________________________

11. Describe the skater’s kinetic energy at the bottom of the ramp.The skater’s kinetic energy is at its maximum when he is at the bottom of the ramp because that is the point where the greatest amount of total energy is converted into kinetic movement energy._____________________________________________________________________________________

12. Describe the skater’s potential energy at the bottom of the ramp.The skater’s potential energy is at its lowest when he is at the bottom of the ramp because that is the point when the greatest amount of the skater’s potential gravitational energy is converted to kinetic energy due to the effects of gravity._____________________________________________________________________________________

13. What happens when the skater is dropped onto the ramp from above? (Hint: look at the bar graph.)When the skater is dropped onto the ramp, his potential energy is at its maximum and there is no kinetic energy, assuming the skater isn’t moving yet._____________________________________________________________________________________

What happens to the total energy when the skater is dropped onto the ramp from above? (Again, look at the bar graph.)

The total energy the skater has is determined when he is dropped on the ramp because that total energy is completely potential energy. The amount of potential energy the skater has is effected by the elevation of the skater is at. For example, when the skater is placed at a higher elevation, then the amount of potential energy or total energy will increase. The amount potential gravitational energy the skater has is equal to the total energy the skater has when he is dropped onto the ramp. _____________________________________________________________________________________

14. Observe the following situations. Draw the possible bar graphs for the situation shown. Compare your results with a nearby lab group, AFTER you have completed this section.

Top of the ramp, stopped for just an instance.

Bottom of the ramp, zooming past the middle.

Mid-way down the ramp, moving about mid-speed.

3/4 of the way down the ramp, moving pretty fast.

15. Draw where the skater might be based on the bar graphs shown. Compare your results with a nearby lab group, AFTER you have completed this section.

16. Consider this zany track. What point or points on this track would the skater have ...

The most kinetic energy? C

The most potential energy? A

The same kinetic energy (two points) B and E

Part II: Track Playground

Click the ‘Track Playground’ tab at the top. Using the track pieces in the upper right of the page, build a track with a single loop, like the track shown in the picture below. Be sure the far left and far right of the track are higher than the loop.

Turn on the ‘Bar Graph,’ ‘Grid,’ and options. For now, set the ‘Friction’ option to ‘Off,’ and the ‘Stick to Track’ option ‘On.’

Using the grid, what is the height of the top of the loop: about 5 metersTry placing your skater at different starting points on one side of the track.

17. What is the minimum height you can place the skater so that he makes it all the way around the loop?The minimum height you can place the skater so that he makes it all the way around the loop is a little over 5 meters or a little over the height of the top of the loop._____________________________________________________________________________________

18. Explain, in terms of energy, why the skater must be at the height in question 17 to make it through the loop.

The skater must be at the height in question 17 to make it through the loop because the skater must exert enough force when he is at the bottom of the ramp. The amount of force the skater exerts depends on the

amount of energy the skater has. The amount of energy the skater has is depended on the height the skater starts at because then he will gain potential gravitational energy which will be converted to kinetic movement energy. The skater must be placed at 5 meters because the height of the loop is 5 meters. I know that Newton’s 3rd law, which is when the amount of force an object exerts and the amount of force rebounded back into an object is equal, will allow the object, which is the skateboarder, to have enough energy, which is “5 meters worth of energy,” rebounded back into him when he hits the bottom of the ramp to propel him around the loop. However, if the skater had only “5 meters worth of energy”, then he would stop completely at the top of the loop, assuming the track has a perfect line of symmetry. The skater will need a little more energy to push him past the top of loop; therefore, the skater needs to be placed a little higher than the loop. _____________________________________________________________________________________

19. With the friction off, does the kinetic energy ever get as high as the total energy? If so, when? If not, why?

With the friction off, the kinetic energy won’t get as high as the total energy because there isn’t a point where that is possible when the entire skater’s potential gravitational energy, which he gained by when being dropped, is converted to kinetic movement energy. _____________________________________________________________________________________

Set the ‘Friction’ option to ‘On.’

20. With the friction off, does the kinetic energy ever get as high as the total energy? If so, when? If not, why?

(Skip this question)_____________________________________________________________________________________

21. Now with the friction on, what is the minimum height you can place the skater so that he makes it all the way around the loop? Is this different than if friction were turned off?

I need to place the skater at approximately 12 meters so that he makes it all the way around the loop. This is different than if the friction was turned off because the skater’s kinetic movement energy, which he got once his potential gravitational energy was converted to kinetic movement energy, is converted to kinetic thermal energy. When there was no friction, the skater’s kinetic movement energy did not convert to kinetic thermal energy. Since there is friction, the skater must be placed at 12 meters, which is a higher elevation before when the friction was off, because of the fact that he will lose his total energy from friction but have enough left to be convert to kinetic movement energy to travel around the loop. If the skater was placed at 5 meters, he won’t make it around the loop because he would have converted too much of his energy to kinetic thermal energy and won’t have enough energy converted to kinetic movement energy to travel around the loop. _____________________________________________________________________________________

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22. In one of the previous questions, we say you may have “lost,” or “dissipated” some energy. Where is this energy going according to your bar graph? What does this mean in real life?

The energy is being converted to kinetic thermal energy, according to my bar graph. This means that if an object, which is the skater, is moving since it has kinetic movement energy and is rubbing against another object, which is the ramp, then friction will occur, which will convert the kinetic movement energy to thermal energy, and slow object down and eventually stop because the object will lose the kinetic movement energy to move.

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23. Energy can be dissipated (or “lost”) in another way on this simulation. What is one more way that you can find that you will “lose” energy?

One more way that energy can be “lost’ is from converting kinetic movement energy to kinetic sound energy. As the skater moves, the skateboard vibrates, which converts kinetic movement energy to kinetic sound energy, or sound. _____________________________________________________________________________________

Create a track of your own. Draw in the diagram below. Label where on the diagram you have the greatest kinetic energy, the greatest potential energy, and two places that have the same potential energy.

Greatest potential energy

Same amount of potential energy

A

B

CD

E

Greatest amount of kinetic energy

F