PHYS 1401 Lab-03: Conservation of Energy
Name: __________________________

Objectives:
· To verify the conservation of mechanical energy by determining the relationship between kinetic energy and potential energy.

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, we will look at the conversion of energy between gravitational-potential energy, work, and kinetic (or moving) energy.

1. Open PhET simulation Energy Skate Park

https://phet.colorado.edu/sims/html/energy-skate-park/latest/energy-skate-park_all.html

This simulation allows you to explore the motion and energetics of a skater riding along a track.

2. Click on “Intro” to get started.

3. You can click and drag the skater to any location and release the skater from rest. Watch the skater skate up and down the track.

4. Click on the “Energy” to see the relative magnitudes of the kinetic, potential, thermal, and total energies as a function of the skater’s position. You can select “Slow Motion” below the track for a more accurate observation.

5. Play around with the simulation. Click on the “Reset” button before answering the questions.

Activity-1
Question-1: How does the skater’s kinetic energy change as he moves down the ramp?

Question-2: How does the skater’s kinetic energy change as he moves up the ramp?

Question-3: How does the skater’s potential energy change as he moves down the ramp?

Question-4: How does the skater’s potential energy change as he moves up the ramp?

Question-5: How does the skater’s total energy change as he moves down the ramp?

Question-6: How does the skater’s total energy change as he moves up the ramp?

Because we are ignoring friction, no thermal energy is generated and the total energy is the mechanical energy, the kinetic energy plus the potential energy. E = K + U.

Question-7: As the skater is skating back and forth, the total energy of the skater is _________

Ignoring friction, the total energy of the skater is conserved. This means that the kinetic plus potential energy at one location, say E1 = K1 + U1, must be equal to the kinetic plus potential energy at a different location, say E2 = K2 + U2. This is the principle of conservation energy and can be expressed as E1 = E2. Since the energy is conserved, the change in the kinetic energy is equal to the negative of the change in the potential energy: .

Default mass is 60 kg. Change the mass of the skater to 100 kg or 20 kg.

Question-8: Is the law of conservation of energy affected by the mass of the skater?

Question-9: Does mass of the skater affect the magnitudes of the kinetic and potential energy?

Activity-2
At the bottom of the simulation window, click on “Playground”. For this part of the activity, you should have the “Friction” slider set to none, which means no thermal energy is generated. Select the “Show Grid” option. Then, add a track by clicking and dragging on a new track (the shape with three circles in the bottom left of the window) and placing it near the skater. You can then click and drag on individual circles to stretch and/or bend the track and make it look as shown below. The bottom of the track should be 1 m above the ground, and both ends of the track should be at a height of 7 m.

Place the skater on the track 7 m above the ground and look at the resulting motion and the Bar graph showing the different energies. Assume the mass of the skater is 75.0 kg and that the acceleration of gravity g = 10 m/s2.

Important Formula: ;

Question-10: How much potential energy does he have at 7.0 m?

Question-11: How much kinetic energy at 1.0 m?

Question-12: How will account for the difference in answers for Q#10 and Q#11?

Question-13: A 20.0 kg skater that starts his skate 10m high (on the earth) would have a potential energy of __________ and a kinetic energy of ________ before his skate. At the lowest point (close to Earth surface), the skater would have a potential energy of ______ and a kinetic energy of ________.

Activity-3
At the bottom of the simulation window, click on “Playground”. You should have the “Friction” slider set to none, which means no thermal energy is generated. Then, add a track by clicking and dragging on a new track (the shape with three circles in the bottom left of the window) and placing it near the skater. You can then click and drag on individual circles to stretch and/or bend the track and make it look as shown below.

Question-14: If the skater starts at point A, will he have enough energy to make it all the way to the point G? why or why not?

Question-15: At which point will the skater have maximum kinetic energy?

Question-16: At which point will the skater have maximum potential energy?

Question-17: If there is lots of friction, will the skater starting at point A make it all the way to point G? Explain.

Complete the table of Kinetic and Potential Energies: use g = 10. m/s2 (1/2 pt each)

Mass of skater m (kg)

Height h

(in m)

Velocity v

(in m/s)

Kinetic Energy K

(in Joules)

Potential Energy U

(in Joules)

20. kg

14 m

12 m/s

1.

2.

60. kg

0.0 m

3.

1470 J

4.

0.20 kg

18 m

0.0 m/s

5.

6.

7.

6.0 m

5.0 m/s

8.

600. J

5.0 kg

9.

10.

160 J

850 J

Conclusion:

Question 18: At the highest point kinetic energy is zero / maximum while the potential energy is

zero / maximum.

Question 19: At the lowest point kinetic energy is zero / maximum while potential energy is zero / maximum.

Question 20: Mass affects / does not affect the conservation of energy.

Question 21: When there is friction, total energy is conserved/ not conserved.