You can visualize this in the simulation. Select the Measurement option for the simulation, and then select the grid and reference options in lower left hand corner. Now, place the skater on the track, allow them to move for a short time, and then pause the simulation. Place the measurement tool on a recorded position (pink dot on the track), and then move the reference bar until this position lines up with a reference line (the height measurement should be 0 m, or very close to it). Your simulation should look something like the image below: Pie Chart Speed Stick to Track VLWW Friction Energy Kinetic 862.1 J Potential -0.1 J 9.8 m Thermal 0.0 J 0 m Height = 0.00 m Total Speed = 5.36 mis 862.0 J Earth Mass 60 kg 75 100 Normal Reference Height . Slow Restart Skater Energy Skate Park PHET : In this setup, your Initial Position is taken as the reference line where Position and Gravitational Potential Energy are 0 (or very close to it given measurement uncertainty). Set the simulation up so you have the correct reference. Now move the reference bar up so that the recorded position (pink dot) you've chosen is on the next horizontal line. Record the Position and Potential Energy. Move the reference bar back to the initial position and repeat the previous steps but move the reference bar down. Once you've recorded those values, change your initial position (reference bar does not start on the chosen recorded position) and move the bar either up or down 1 horizontal line. Fill out the table below (note: make sure to keep Gravity at 9.8 m/s" and Mass at 60 kg). Initial Position (m) Final Position(m) Change in Position (m) Change in PE (J) Ref. Bar Moved Up 0 Ref. Bar Moved Down 0 Student Choice As you can see, it doesn't matter where you start, the magnitude of the change is not affected by the choice of Origin. The Work-Energy Theorem states: (Net Work) = (Change in KE). For Conservative Forces, we can state: (Work) = =(Change in PE). Hence, when only Conservative Forces are actors, we can make the statement: (Net Work) = (Change in KE) = -(Change in PE). This allows us to very quickly, and easily, solve many problems when dealing with these forces (i.e., gravity and electric fields). In the simulation, choose the playground option and reset the simulation. Make sure that the 'Speed', and 'Stick to Track' are selected. Next, create a track that acts as a type of ramp (the skater starts at some height and leaves the ramp at a height 2 m lower). Measure the Initial and Final Heights, and the Velocity right before the Skater leaves the track. Input the data in the table and then use your knowledge of Physics to calculate the change in each Potential and Kinetic Energy. (NOTE: In order to measure speeds, use the frame-by-frame button to be as precise as possible) The Energy Uncertainties are: OKE = mvov OPE = mg(Oh, + oh,) ( is the velocity uncertainty, Oh, is the initial height uncertainty, & Oh, is the final height uncertainty) Simulation Constants Mass (kg) Gravity (m/s2) Value Uncertanty Initial Height (m) Final Ramp Height (m) Final Velocity (m/s) Change in KE (J) Change in PE (J)