Three quick demonstrations, three chances to be surprised — and then explain exactly why you shouldn't have been, using Newton's First Law. Predict first, every time. The prediction is the point.
🎯 Goals
Predict and observe three demonstrations that isolate inertia from other effects.
Explain each demonstration's outcome using Newton's First Law, not just 'it just does that.'
Compare the inertia of two objects with different masses through direct observation.
Distinguish 'friction stopped it' from the myth that motion 'runs out' on its own.
🧰 Materials
🃏Index card, a cup, and a coin (for the coin drop demo)
📦Two identical boxes or containers — one empty, one filled with books or sand
🛼A cart, puck, or ball, plus a smooth surface and a rough surface to compare
📓Physics notebook
Section 1 of 4
Station 1 — The Coin Drop
1
Balance an index card on top of a cup, and place a coin on top of the card.
Before doing anything else, predict: if you flick the card away quickly, what happens to the coin?
2
Flick the card sideways, quickly and sharply.
Watch closely — does the coin fly off with the card, or does it drop straight down into the cup?
3
Explain the result using Newton's First Law.
The coin was at rest. The quick flick barely has time to drag the coin along with the card — once the card is gone, the coin's inertia keeps it exactly where it was, and gravity takes over from there.
Section 2 of 4
Station 2 — Light vs. Heavy
4
Set up two identical containers — one empty, one loaded with books or sand.
Predict which one will be harder to get moving with a gentle push, and which will be harder to stop once it's sliding.
5
Give each container the same gentle push, and then try to stop each one with the same light touch.
Pay attention to how much effort each step actually takes for each container.
6
Connect what you felt to inertia and mass.
More mass means more inertia — more resistance to starting, and more resistance to stopping.
Section 3 of 4
Station 3 — Rolling to a Stop
7
Roll the same object with the same starting push across a smooth surface, then across a rough one.
Predict which surface will let the object travel farther before stopping.
8
Compare how far the object traveled on each surface.
The object should travel noticeably farther on the smoother surface.
9
Explain why the object eventually stops on BOTH surfaces — but for the same underlying reason.
It's not "running out" of anything. Friction (more of it on the rough surface, less on the smooth one) is an actual backward force acting the whole time. Remove friction entirely, and the object wouldn't stop at all.
⚠️ Resist the urge to say the object 'runs out of energy to move.' Name the specific force causing the slowdown instead.
Station 1 — The Coin Drop
Prediction (before)
What Happened
Newton's First Law Explanation
Station 2 — Light vs. Heavy
Prediction (before)
What Happened
Newton's First Law Explanation
Station 3 — Rolling to a Stop
Prediction (before)
What Happened
Newton's First Law Explanation
📓 Physics Notebook
Of the three stations, which result would have surprised you most before this class? What about Newton's First Law makes sense of it now?
Section 4 of 4
Conclusion
Question 1
Explain the coin drop demonstration using the words 'inertia' and 'net force' correctly.
Question 2
Why did the heavier container feel harder to both start and stop, while the lighter one felt easier for both? Connect your answer to mass and inertia.
Question 3
A classmate says a rolling ball eventually 'runs out of force.' Rewrite their explanation correctly, using Newton's First Law.
📤 Turn In
Completed station log — prediction, observation, and Newton's First Law explanation for all three stations