Force And Laws Of Motion

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• Questions
• Summary

A force is anything that can cause a change to objects. Forces can:

1. Change the shape of an object
2. Move or stop an object
3. Change the direction of a moving object.

A force can be classified as either a contact force or a non-contact force.

A contact force must touch or be in contact with an object to cause a change. Examples of contact force is:

• The force that is used to push or pull things, like on a door to open or close it.

A non-contact force does not have to touch an object to cause a change. Examples of non-contact forces are:

• The force due to gravity, like the Earth pulling the Moon towards itself
• The force due to electricity, like a proton and an electron attracting each other

The unit of force is the Newton (symbol N).

Effect of force:

1. Force can make a stationary body in motion. For example, a football can be set to move by kicking it, i.e. by applying a force.
2. Force can stop a moving body – For example, by applying brakes, a running cycle or a running vehicle can be stopped.

Forces are mainly of two types :

1. Balanced forces
2. Unbalanced forces

Balanced Forces

If the resultant of applied forces is equal to zero, it is called balanced forces.

1. Example, in the tug of war, if both the team apply similar magnitude of forces in opposite directions, the rope does not move in either side. This happens because of balanced forces in which resultant of applied forces become zero.
2. Balanced forces do not cause any change of state of an object. Balanced forces are equal in magnitude and opposite in direction.
3. Balanced forces can change the shape and size of an object. For example, when forces are applied from both sides over a balloon, the size and shape of the balloon is changed.

Unbalanced Forces

If the resultant of applied forces are greater than zero, the forces are called unbalanced forces. An object in rest can be moved because of applying balanced forces.

Unbalanced forces can do the following :

1. Move a stationary object
2. Increase the speed of a moving object
3. Decrease the speed of a moving object
4. Stop a moving object
5. Change the shape and size of an object