What it shows
Objects keep their state of rest unless a force acts on them. When the card is flicked quickly, the coin does not move sideways and drops straight down into the glass.
The science
Inertia is the tendency of an object to stay at rest or keep moving in a straight line unless a force acts on it. The more mass an object has, the more inertia it has. When the card is flicked quickly, friction acts on the coin for such a short time that it cannot move the coin sideways much. With nothing under it, the coin falls down because of gravity into the glass.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A glass or steel tumbler
- A smooth playing card or a piece of stiff card
- A coin, 5 rupees
- A stack of 5 coins or carrom pieces
- A thin ruler
- A plastic tray
- A sheet of paper and a bottle with a wide base
Safety
For this project: Use unbreakable steel or plastic tumblers for children under 8. Keep fingers away from the edge when flicking.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Put the card on top of the glass and place the coin in the middle of the card, over the glass opening.
Hold the card at one side and flick it sharply with a finger so it shoots out sideways.
Watch the coin drop straight into the glass. If it flies out, flick faster and more horizontally.
Stack five coins or carrom pieces on a table and strike the bottom one quickly with a ruler. Watch the others stay in place and fall down.
Place a sheet of paper under a bottle and try pulling the paper out slowly, and then quickly, and compare.
Try the experiment with heavier and lighter coins and note which stays better.
Draw pictures of the objects before and after the flick, with arrows for the force.
List three everyday examples of inertia, such as passengers lurching forward when a bus brakes.
What you should see
The coin falls into the glass, the stack of coins stays standing, and the bottle stays in place when the paper is pulled quickly but moves when it is pulled slowly.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is inertia?
The tendency of a body to stay at rest or keep moving unless a force acts on it.
2Why does the coin fall into the glass?
It stays in place when the card is flicked out, and then gravity pulls it down.
3Why does a fast pull work better than a slow pull?
Friction has less time to drag the coin along.
4Why do passengers lurch forward when a bus stops?
Their bodies tend to keep moving at the earlier speed.
Take it further
Measure how the speed of the pull changes the sideways movement of the bottle using a marked paper strip.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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