Acceleration down a ramp
What students will learn
- Describe how speed changes when something rolls downhill
- Read acceleration as the slope of a velocity graph
What you'll need
- Motion sensor
- A cart or any toy car that rolls straight
- A board or track, about 1 meter
- A few books to prop up one end
Setup
Prop one end of the board on two or three books to make a gentle ramp. Attach the motion sensor to the cart, or aim a distance sensor down the ramp. Steeper is not better: a gentle slope gives cleaner data.
What students do
- Hold the cart still at the top of the ramp and start recording.
- Release the cart. Do not push it.
- Stop recording when the cart reaches the bottom.
- Look at the velocity graph together. Is it a straight line?
- Add one more book and repeat. Compare the two slopes.
What to expect
The velocity graph is close to a straight line, and it gets steeper when the ramp does. Students see that "speeding up steadily" looks like a straight, rising line. Friction makes the line slightly curved at low speeds; that is worth pointing out, not hiding.
Teaching notes
The most common mix-up is reading the velocity graph as a picture of the hill. Ask "what would this graph look like on a steeper ramp?" before running it, then test the predictions.