You are here
š¬ Think about it
A kick sends a ball moving, a bat changes a ball's direction, and your fingers squeeze a lemon. All three are forces doing different jobs. So what exactly is a force, and what do we need to describe it fully? Let us see.
What can a force do?
What can a force change?
A force
Changes motion or shape
1. Its motion
Start, stop, speed, turn
Example:
A kicked ball moves
2. Its shape
Squeeze or stretch it
Example:
A squeezed lemon
- It can make an object move from rest.
- It can change the speed of a moving object.
- It can change the direction of motion.
- It can even change the shape of an object.
Example:
A bat changes a cricket ball's direction; fingers squeeze and change a lemon's shape.
Why is direction important for a force?
Force
Magnitude
how strong — measured in newton (N)
Direction
which way it acts — always stated
↓
A
force
needs
both
a magnitude and a direction. Change either one and the effect changes.
Why the Direction Always Comes With It
Friction
acts
opposite
to the direction of motion
↓
Gravitational force
acts
towards
the Earth
↓
Buoyant force
acts
upwards
on an object in a liquid
↓
Change the magnitude or the direction, and the effect of the force changes too
- Force is a quantity that needs both magnitude and direction.
- Its magnitude expresses its strength.
- The SI unit of force is the newton (symbol N).
- If the magnitude or direction changes, the effect of the force changes.
Example:
Friction acts opposite to motion; the Earth's gravitational force pulls objects downward — each has a definite direction.
š Note
- If either the magnitude or direction, or both, of a force change, the effect of the force also changes.
Important Points
- A force can start, stop, speed up, slow down, redirect or reshape an object.
- Force has both magnitude and direction.
- The SI unit of force is the newton (N).
Important Definitions
- Force — a push or pull that can change the motion or shape of an object; it has magnitude and direction.
- Newton (N) — the SI unit of force.
