Muscular force : The force applied with the muscles.

• All the actions of our body are performed with the help of bones and muscles. These movements are clue to muscular force.
• Lifting up luggage, carrying school bag to the school, riding a bicycle, playing games like cricket, football, weight-lifting exercises, etc. are the tasks done in our clay-to-day life by using muscular force.

Mechanical force : The force applied with the help of machines.

For doing many tasks with ease, we use machines. Some machines are used with our muscular energy while some are automatic machines which work on electricity or fuel. The force applied by means of a machine is called mechanical force.

Gravitational force : The force applied by the earth to pull the objects towards itself.

• The earth pulls everything towards itself.
• Sir Isaac Newton discovered gravitational force in the 17th century. When any object is thrown in the upward direction, the force of gravity or gravitational force starts acting on it.
• This force acts in the direction opposite to that of an object moving upwards.
• The speed of object going upwards, goes on decreasing and then becomes zero. Then this object starts falling down due to gravitational force. Its speed also increases with the force of gravity.

The gravitational force operates between the sun and the planets in the solar system. Because of this, the planets revolve around the sun. At the same time, gravity also operates between planets and their satellites.

Frictional force : The force created by the two surfaces upon each which is against the direction of the motion.

• When two surfaces are rubbed against each other, the force of friction is created.
• This force always acts against the direction of motion. We use force of friction in our daily life.
• The brakes applied for stopping the vehicle helps to create frictional force.
• Due to the force of friction, we are able to walk on the ground without slipping. On the other hand, oily or wet floor, offers less frictional force and hence one can easily slip on such floors.
• The force of friction can be increased or decreased as per our requirement.

Electrostatic force : The force exerted by electrostatically charged materials.

• Static electricity is produced on the substances such as rubber, plastic, ebonite, etc. due to friction. These substances become electrically charged.
• The force exerted by the electrically charged substance is called electrostatic force.