Predict first, every time — then race the carts to find out if F = ma agrees with your gut. Most of today's value is in noticing when your prediction and the result don't quite match, and figuring out why.
🎯 Goals
Predict how changing mass affects acceleration for a constant force, and test the prediction.
Predict how changing force affects acceleration for a constant mass, and test the prediction.
Use F_net = ma to calculate acceleration when net force and mass are known.
Explain why two different masses fall at the same rate under gravity alone.
🧰 Materials
🛒Two identical carts, plus add-on masses
🎗️A consistent force source — rubber band, or string over a pulley with a hanging weight
⏱️Stopwatch or motion detector
🪨Two very different masses for the falling-objects drop (e.g. a golf ball and a tennis ball)
📓Physics notebook
Section 1 of 4
Race 1 — Same Force, Different Mass
1
Set up two identical carts, one loaded with extra mass.
Rig your force source (rubber band or hanging weight) so it applies the same force to both carts.
2
Predict which cart will accelerate faster, and by roughly how much, before testing.
Use F = ma reasoning in your prediction, not just a guess — write down the relationship you expect.
3
Release both carts with the same applied force and observe.
Time them over the same distance, or just watch which one visibly gets ahead.
Section 2 of 4
Race 2 — Same Mass, Different Force
4
Reset to two identical carts (same mass), but apply a stronger force to one than the other.
A tighter rubber band stretch, or a heavier hanging weight, works for increasing force.
5
Predict which cart accelerates faster this time, and test it.
This time mass is held constant — only force is changing, so your prediction should reason from that instead.
Race 1 — Same force, different mass
Prediction (before racing)
What actually happened
Did it match? Why or why not?
Race 2 — Same mass, different force
Prediction (before racing)
What actually happened
Did it match? Why or why not?
📓 Physics Notebook
Did either race surprise you? If your prediction and the result didn't quite match, what do you think caused the gap — a flaw in your reasoning, or something messy about the real-world setup (friction, an uneven push)?
Section 3 of 4
The Falling Objects Puzzle
6
Hold your two very different masses at the same height and predict what happens if you drop them together.
Most people's gut says the heavier one falls faster — write down your honest prediction before testing.
7
Drop both objects at exactly the same instant and watch closely.
Try it a few times to make sure what you're seeing is real and not a timing fluke.
8
Explain the result using F = ma.
Write out a = F_g/m = mg/m = g for both objects, showing exactly why mass cancels out of the calculation.
Section 4 of 4
Conclusion
Question 1
Using your Race 1 data, explain in your own words why more mass produced less acceleration for the same force.
Question 2
Using your Race 2 data, explain why more force produced more acceleration for the same mass.
Question 3
A classmate insists heavier objects must fall faster because they weigh more. Use F = ma to correct their reasoning.
📤 Turn In
Completed race log — predictions, results, and whether they matched, for both races
Your F = ma explanation of the falling-objects result