Forces

Force

A force is a push or a pull.

Instrument to measure force

A newton meter (or spring balance).

Effect of force on an object

It can change the speed of the object.

It can change the shape of the object.

Second effect of force on an object

Friction

Friction is a force that opposes motion between two surfaces in contact.

Reducing friction

Use lubrication (like oil) or make surfaces smoother.

Bicycle brakes after rain

Water reduces the friction between the brake pad and the wheel rim.

Weight of an object

The force of gravity acting on it.

Hooke's Law

Hooke's Law states that the extension of a spiral spring is directly proportional to the applied force, as long as the spring is not overstretched.

Effect of unbalanced force

Accelerate or change motion.

Balanced forces on a car

Continue moving at 30 km/h.

More force pushing forward

Speed up.

Force opposing motion

Friction.

Usefulness of friction in cars

It allows tyres to grip the road so the car can move and stop safely.

Force against a moving block

Friction.

Reducing friction on a block

By using a smoother surface or adding lubrication.

Friction force on a pulled block

6 newtons (equal and opposite to the pulling force).

Changes when going to the moon

The weight changes (mass stays the same).

Neil Armstrong's weight on the Moon

Because the Moon's gravity is one-sixth that of Earth's.