Quick answer: Projectile motion combines a constant horizontal velocity with a vertical motion of constant acceleration g = 9.81 m/s² downwards. This Physics 11-12 lab on projectile motion 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.
A marble rolling off a table follows a curved path, but its fall time depends only on the table height. In this lab you test that idea by launching the marble at three different speeds, and you use the measured ranges to calculate the launch speeds without a stopwatch.
Level: Physics grades 11-12 (A Level · IB · Class 11-12) · Curriculum: A Level 3.4
Aim
To show that the time a marble takes to fall from a table is the same for different launch speeds, and to find the launch speed from the measured range.
Equipment
- Curved ramp or grooved ruler, marble
- Table of known height H (measure it with a metre rule)
- Sheet of paper with carbon paper on top, tape
- Metre rule, books to change the release height
Safety
Keep the floor around the landing area clear so that nobody slips on a rolling marble. Place a box behind the landing area to catch stray marbles, and do not stand in the line of the launch.
Method
- Measure the height H from the bottom of the marble at the table edge to the floor.
- Fix the ramp so that the marble leaves the table edge horizontally.
- Release the marble from rest at three different heights on the ramp: low, medium and high.
- For each height, release the marble five times and mark where it lands on the carbon paper. Measure the average range from the table edge.
- Calculate the time of fall t = √(2H ÷ g) and the launch speed v = x ÷ t for each release height.
Results
The table height is H = 0.85 m. Mean ranges (each from five landings):
| Release | Mean range x (m) | Spread of landings (m) |
|---|---|---|
| Low | 0.62 | ±0.01 |
| Medium | 0.84 | ±0.01 |
| High | 1.03 | ±0.01 |
Analysis questions
Question 1 Time of fall
Calculate the time of fall of the marble from the table of height 0.85 m.Question 2 Launch speeds
Calculate the horizontal launch speed for each release height.Question 3 Same time of fall
Explain why the time of fall is the same for all three release heights.Question 4 Percentage uncertainty
Calculate the percentage uncertainty in the range for the low release and the high release.Question 5 Prediction
Predict the range for the low release if the table were 1.20 m high.Question 6 Impact speed
Calculate the speed of the marble as it hits the floor after the high release.Question 7 Sources of error
Suggest two reasons why the marble might land slightly short of the predicted range.Question 8 Improvement
Describe one improvement that would make the speeds more reliable.
