2
Big force, small force
Workbook 2: Topic 2.1, pp. 19–21
GoalSay that forces can be big or small, and choose the right size of force for a job.
New words
big force · a strong push or pullsmall force · a gentle push or pullheavy · hard to lift because of how much it weighs
Explanation
Forces can be big or small. A big force is a strong push or pull. A small force is a gentle one. You need only a small force to pick up a sheet of paper. You need a big force to pull a sledge with a friend sitting on it. A heavy thing usually needs a bigger force to move than a light thing. The harder you push or pull, the bigger the force is.
Worked examples
A heavy box is hard to push, so Kenji needs a big force. A feather needs only a small push.
Pressing a button on a phone takes a small force. Pushing a car that has run out of petrol takes a very big force.
If you push a toy car gently, it rolls a short way. If you push it harder, it rolls farther.
Class activity
Big and small forces (with an adult): choose five things from home, such as a ball, a book, a cushion, a toy car and a full water bottle. Push each one across the floor. Is it a small force or a big force? Put the things in order from smallest force to biggest force. Predict first, and then check. Do not push anything that is too heavy to move safely.
Practice
1
Which needs a big force to move: a feather or a bicycle?
The bicycle (B).
2
Ravi turns a page of a book. Does he use a big or a small force?
A small force.
3
A bus is full of people. Does it need a big force or a small force to start moving?
A big force.
4
The long arrow shows the size of the push on the box. Is it a big force or a small force?
A big force.