Inertia: the sudden stop
Run a trolley carrying a block into a stopper and watch the block keep going. Change the speed, the block's mass and whether it is strapped down.
Core concept
Objects keep moving at the same velocity unless a force acts on them (Newton's first law)
Topic: Force and motion
Inertia is the tendency of an object to keep doing what it is already doing: a still object stays still, and a moving object keeps moving at the same speed: How far something travels in a certain time, like kilometres per hour. All key words in a straight line, unless a force: A push or a pull. Forces can start, stop or turn things. All key words acts on it. This is Newton's first law of motion. The more mass: How much matter something has, measured in grams or kilograms. It is the same everywhere. All key words an object has, the more inertia it has, and the bigger the force needed to start or stop it. That is why passengers lurch forward when a bus brakes suddenly, and why seat belts save lives.
What you will learn
- State Newton's first law of motion.
- Explain why a loose object keeps moving when its support stops.
- Explain why a heavier object needs a bigger force to stop it quickly.
Before you start
- Know that a force can change an object's motion.
Materials
- Wooden blocks of 0.25 kg, 0.5 kg and 1 kg
- Elastic strap
Equipment
- Trolley and runway
- Low stopper fixed to the bench
Procedure
- Run the trolley slowly into the stopper with the block loose, and record what happens.
- Run it fast with the block loose and compare.
- Strap the block down and run the trolley fast again.
- Use the heavier block and compare the force needed to stop it.
How this simulation is simplified
- g is taken as 10 N/kg, and friction between the block and the surface is 0.3 of its weight.
- The trolley stops in 0.1 s.