5.1 What Is a Force?
A Ride Full of Forces
Sonali and Ragini set off cycling on a windy day. The wind pushed against them (“we’re riding against the wind — pedal harder!”). Some stretches of road were rough and hard to pedal, others smooth. They rang their bells, turned the handlebars to change direction, and braked. Then, freewheeling down the hill, they sped up without pedalling at all — “something is pulling us downhill, what could it be?”
Every single thing in that ride — the wind, the rough road, the turning, the speeding up downhill — is a force at work. This chapter is about all of them.
Activity 5.1 — Move a box every way you can Take a big cardboard box and try to move it in as many ways as possible — push it, pull it, lift it, carry it. Whatever you try, every method comes down to one of two things: a push or a pull.
The Definition In science, a force is a push or a pull applied on an object. More precisely, a force is a push or pull on an object that results from its interaction with another object. The SI unit of force is the newton (written with a small “n”), symbol N.
Forces need two objects
When you push a table, your hand is one object and the table is another — they are interacting. Look back at any pushing or pulling you can think of: a foot kicking a ball, a magnet pulling a pin, the Earth pulling a falling fruit. In every case there are at least two objects. A force never appears on its own; it is always the result of two (or more) things interacting.
Science Talk Here’s something to feel for yourself: push hard against a wall. Your hand pushes the wall — but do you also feel the wall pushing back on your hand? Stop pushing, and that feeling vanishes instantly. Whenever two objects interact, each one feels a force from the other, and the forces disappear the moment the interaction ends. (You’ll explore this “two-sided” nature of forces much more in higher grades.)
Exam Tip Two quick facts that earn easy marks: a force is a push or pull, and its SI unit is the newton (N) — always a small “n” in the word, capital “N” in the symbol. Weight, being a force, is also measured in newtons.