Quick answer: Linear momentum is the product of mass and velocity, p = mv, a vector in kg m/s. This AP Physics 1 lab on impulse momentum theorem gives the aim, the equipment, the safety points, a step-by-step method, sample results and 8 analysis questions; the answers are on a separate page and the lab sheet is a free printable PDF.
Does a softer surface change the impulse on a bouncing ball, or only the force? In this lab you use a slow-motion phone video to measure the rebound height and the contact time on three surfaces, then calculate impulse and average force. Everything fits on a table or a kitchen floor.
Level: AP Physics 1 (algebra-based) · Curriculum: AP P1 Unit 4
Aim
To find the impulse and the average force on a ball bouncing off three different surfaces by measuring its drop height, its rebound height and the time of contact.
Equipment
- Tennis ball (mass about 57 g; weigh it on a kitchen scale)
- Metre rule fixed upright beside the drop point
- Phone with a slow-motion camera mode (240 frames per second)
- Three surfaces: a hard floor tile, a piece of carpet and a thick foam mat
Safety
Keep the area clear of people and breakable items. Do not stand on chairs to drop the ball from high places. Pick up balls at once so nobody trips.
Method
- Find the mass of the ball and fix the metre rule vertically beside the first surface.
- Place the phone on a stand at floor level, pointing at the ruler, and start the slow-motion recording.
- Release the ball from rest with its lowest point at the 1.50 m mark.
- Play the video back frame by frame. Read the highest point reached after the bounce (h₂) from the rule.
- Count the frames in which the ball touches the surface. At 240 frames per second, each frame lasts 1/240 s = 0.0042 s.
- Repeat for the carpet and the foam mat, always releasing from 1.50 m.
Results
Sample data for a ball of mass 0.057 kg dropped from 1.50 m:
| Surface | Rebound height h₂ (m) | Frames in contact |
|---|---|---|
| Hard tile | 0.83 | 3 |
| Carpet | 0.62 | 4 |
| Foam mat | 0.35 | 6 |
Analysis questions
Question 1 Speed before impact
Calculate the speed of the ball just before it hits any surface, using energy conservation from the 1.50 m drop.Question 2 Speed after impact
Calculate the speed just after impact on each surface from its rebound height.Question 3 Impulse on the ball
Calculate the impulse on the ball on each surface. State the direction convention you use.Question 4 Contact times
Convert the frame counts into contact times in seconds.Question 5 Average force
Calculate the average force from each surface on the ball, and state whether the weight of the ball matters.Question 6 Trend
Describe how impulse, contact time and force change from tile to foam, and explain the trend in terms of energy.Question 7 Uncertainty in contact time
The contact time is uncertain by about one frame. Calculate the percentage uncertainty in the tile result and say how it affects the force.Question 8 Improvements
Suggest two improvements that would give more reliable values of the average force.
