What it does
Inertia is the habit of every object to keep doing what it is already doing: stay still, or keep moving in a straight line at the same speed. This page shows three everyday cases and lets you change the numbers. It is a teaching model with round numbers, not a measurement of a real coin or bus.
In the coin demo a coin sits on a card over a glass. In the bus demo you see which way a passenger leans. In the third demo you push blocks of different mass. When you are ready, step on to newton's laws sandbox for the force rules behind this, or collision carts to see inertia in crashes.
How to use it
- Choose a demo at the top.
- Move the slider and read the sentence under the picture.
- Switch to Class 11 for the extra numbers.
- Answer the quiz questions. They change each time.
What each setting does
- Card speed: how fast the card is pulled. Below about 0.35 m/s the coin rides along; above that the card escapes and the coin drops.
- Bus acceleration: positive means speeding up, negative means braking. The lean is always opposite to the acceleration.
- Mass of the block: a bigger mass is harder to get moving, so it takes longer to reach the same speed with the same push.
Worked example
A 10 kg block gets a 10 N push. Acceleration = 10 ÷ 10 = 1 m/s², so it takes 1 s to reach 1 m/s. A 20 kg block takes 2 s. Same push, double the mass, double the time.
FAQs
Why do I lean forward when the bus brakes? Your feet are slowed by the floor, but the rest of your body keeps its old speed for a moment.
Is inertia a force? No. It is a property of matter. A force is needed to change the motion.
Does a heavier object have more inertia? Yes. Mass is the measure of inertia.
Why does the coin need a fast flick? A fast flick means friction pushes the coin sideways for a very short time, so the coin barely moves sideways and gravity pulls it down.
Where the numbers come from
- Formulas are the standard friction and Newton's second law results. Numbers are round teaching values. Drawings are fibub's own.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-10.