Forces

Gravitational force

The strength of gravitational pull depends on where the object is.
eg.the Earth and the moon.

Gravity is the force of attraction acting on an object on earth.

Gravity gives weight to physical objects and causes them to fall toward one another.

apple falling onto Earth

Magnetic force

bar magnet

The force of attraction and repulsion

magnetism flow

horseshoe magnet

Magnetism is the force that moving charges exert on one another.

U-shaped magnet

Elastic spring force

Springs will change its length and shape when it is stretched or compressed.

Spring balances

The force which a spring exerts on whatever is stretching or compressing it .

r

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Frictional force

Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other

Frictional force is lesser on a smooth surface than on a rough one.

when ball rolls there is frictional force between the floor and the ball

We can use:
-lubricants
-ball bearings
-wheels

Lubricants

Wheels

Ball bearings