• Force: A push or a pull, that changes or tends to change the state of rest or uniform motion of an object or changes its direction or shape.
• A force arises due to the interaction between two objects.
• Force has magnitude as well as direction.
• A change in the speed of an object or the direction of its motion or both implies a change in its state of motion.
• Force acting on an object may cause a change in its state of motion or a change in its shape.
• A force can act on an object with or without being in contact with it.
• Types of Forces:
• Contact Forces: The forces act on a body when the source of force is in actual contact with the body.
(i) Muscular Force: The force exerted by the muscles of the body.
(ii) Mechanical Force: The force produced by a machine.
(iii) Frictional Force: The force that opposes the motion of an object.
• Non-Contact Forces: Forces which do not involve physical contact between two bodies on which they act.
(i) Magnetic Force: A magnet exerts a non-contact force on objects made of iron, steel, cobalt or nickel.
(ii) Electrostatic Force: The force which result due to repulsion of similar charges or attraction of opposite charges.
(iii) Gravitational Forces: The force that exists between any two masses because of their mass.

• Force per unit area is called pressure.
• Liquids and gases exert pressure on the walls of their containers.
• The pressure exerted by air around us is known as atmospheric pressure.