Interactive PhysicsTM

Free Fall Simulation - Falling From Rest

Discussion:

In this activity, you will use the Interactive PhysicsTM program to simulate the motion of a ball falling freely from rest. When you first load the simulation file, it is set up to simulate free fall near the surface of the Earth, where g = 10 m/s2 (approximately). After investigating this motion, you will alter the value of g to simulate free fall on the Moon, where g = 1.63 m/s2.

simulation screen dump
The Interactive PhysicsTM Free Fall Simulation

Procedure:

  1. Double-click on the file "ip_frefall_sim" which you will find in the "Group Shared" folder. This will start the Interactive PhysicsTM software and load the free fall simulation as shown in the diagram at right. (Interactive PhysicsTM software may not be available on all computers.)
  2. When you click "Run" on the toolbar, the ball will begin to fall. Notice how the position, velocity, and acceleration meters change as the ball moves. To stop the simulation, click "Stop" (the "Run" button changes to a stop sign while the simulation is running.). Note that you can start and stop the simulation by alternately clicking "Run" and "Stop". To reset the simulation, click the "Reset" button.
  3. Construct a data table in which you can record the position, velocity, and acceleration for the ball for each half second from 0 seconds to 4 seconds.
  4. Reset the simulation and click "Run". When the timer is near 0.5 seconds, click "Stop". Use the frame advance buttons to move the timer to precisely 0.5 second, and enter the data for position, velocity, and acceleration in your data table. Click "Run" again, and stop the simulation and record your data for 1, 1.5, 2, 2.5, 3, 3.5, and 4 seconds.
  5. Pull down the World Menu, and select "Gravity...". Use the slider to change the free fall acceleration to approximate gravity on the moon (about 1.630 m/s2).

    The Gravity Dialog Box
    The Gravity Dialog
  6. Construct a second data table (be sure to label which data table is which!) in which you can enter the position, velocity, and acceleration of the ball on the moon each half second from 0 to 4 seconds.
  7. Run the simulation and record your data for the moon.

Results:

  1. Construct position vs. time, velocity vs. time, and acceleration vs. time graphs for the motions. You can put the graphs for both the Earth and the Moon on the same set of axes.

Questions:

  1. As the ball falls, what happens to its velocity? (Remember that a quantitative description is superior to a qualitative description...)
  2. As the ball falls, what happens to its acceleration?
  3. How does free fall on the Moon compare to free fall on Earth? (How is it the same, and how is it different?)
  4. For free fall on Earth (g = 10 m/s2), calculate the velocity and distance fallen for a ball starting from rest which falls for 4 seconds. Show a neat and organized calculation. Compare your results with the simulation results.
  5. For free fall on the Moon (g = 1.63 m/s2), calculate the velocity and distance fallen for a ball starting from rest which falls for 4 seconds. Show a neat and organized calculation. Compare your results with the simulation results.
last update October 18, 2002 by JL Stanbrough