Lab Energy of the Tossed Ball
PROCEDURE:
1. Measure and record the mass of the ball you plan to use in this experiment.
2. Connect the Motion Detector to the DIG/SONIC 1 channel of the interface. Place the Motion Detector on the floor and protect it by placing a wire basket over it.
3. Hold the ball directly above the Motion Detector. Have your partner click to begin data collection. Toss the ball straight upward above the Motion Detector and let it fall back toward the Motion Detector catch the ball before it hits the detector.
Note: Use two hands, be sure to pull your hands away from the ball after it starts moving so they are not picked up by the Motion Detector. Throw the ball so it moves vertically above the detector. Verify that the position vs. time graph corresponding to the free-fall motion is parabolic in shape, without spikes or flat regions, before you continue. This step may require some practice. If necessary, repeat the toss, until you get a good graph. When you have good data on the screen, proceed to the Analysis section.
4. Click on the Examine button, , and move the mouse across the position or velocity graphs of the motion of the ball to answer these questions.
• Identify the portion of each graph where the ball had just left your hands and was in free fall. Determine the vertical position and velocity of the ball. Enter your values in your data table. (after release)
• Identify the point on each graph where the ball was at the top of its path. Determine the time, vertical position, and velocity. Enter your values in your data table. (top path)
• Find a time where the ball was moving downward, just before it was caught. Measure and record the vertical position and velocity of the ball at that time. (before catch)
• Collect two more times on the way up and on the way down for a total of seven data points.
• For each of the seven points in your data table, calculate:
Gravitational Potential Energy: Ug =mgy ; Kinetic Energy: K = 1/2mv2 ; and
Total Energy: TE = Ug+KE
DATA TABLE:
Mass of the ball (kg) 0.500
When Time (s) Position (m) Velocity (m/s) Ug (J) K (J) TE (J)
After release 2.30 0.795 1.52 3.98 0.578 4.56
On the way up 2.35 0.871 0.963 4.36 0.232 4.59
Before the Top 2.40 0.893 0.391 4.47 0.0382 4.51
Top of path 2.45 0.904 -0.084 4.52 0.00176 4.52
After the Top 2.50 0.882 -0.514 4.41 0.0660 4.48
going down 2.55 0.854 -0.950 4.27 0.226 4.50
Before catch 2.60 0.794 -1.51 3.97 0.570 4.54
ANALYSIS:
• Use Logger Pro and graph the energies as a function of time. Please show all energies on the same graph and their corresponding mathematical equations
• Inspect your kinetic energy vs. time graph for the toss of the ball. Explain its shape.
• Inspect your gravitational potential energy vs. time graph for the free-fall flight of the ball. Explain its shape.
• Inspect your Total energy vs. time graph for the free-fall flight of the ball. Explain its shape.
• What is the physical meaning of the slope of the total energy vs. time, or of the tangent lines to the curves in the Kinetic and Potential energies vs. time?
• What do you conclude from this graph about the total energy of the ball as it moved up and down in free fall? Does the total energy remain constant? Should the total energy remain constant? Why? If it does not, what sources of extra energy are there or where could the missing energy have gone?
• Insert a graph of velocity vs. time graph. Use the graph and identify the initial, final velocity and displacement of the ball while in your hands. Indicate this in the graph:
Time interval:
Initial velocity Final velocity
Displacement
• Use the Kinetic Energy Work theorem and calculate the net work done on the ball while in your hands.
• Use the definition of Work and determine the net force on the ball while in your hands.
In our case the Net force is directed upward, and the ball is moving up, so
• Create a free Body diagram for the ball while in your hands and calculate the average force applied on the ball during this time.
• For the time that the ball is in the air, what is the sign of the work done by gravity on the way up and on the way down? What happens to the Kinetic and Potential Energies on the way up and down? Associate the changes in Kinetic and Gravitational Potential energies on the way up and down to the work done by gravity and write a statement about it, .
• What is a conservative force? Examples
• What is a non-conservative force? Examples?
• What would change in this experiment if you used a very light ball, like a beach ball?
• Use Logger Pro bar graph option to create an Energy graph.
• What would happen to your experimental results if you entered the wrong mass for the ball in this experiment?
