Type of Forces
The two kinds of forces are:
- Contact forces, and
- Non-contact forces
The forces which act on bodies when they are in actual contact are called the contact forces.
- Frictional force: When body is slided (or rolled) over a rough surface, a force acts on the body in direction opposite to the motion of the body parallel to the surface in contact. This is the frictional force or force of friction.
- Normal reaction force: The equal and opposite force exerted by a surface normally on a body when placed on that surface is called normal reaction force.
- Tension force as applied through strings: The pulling force applied by a string when a body is suspended on it so as to balance the weight of the body is called tension force T ( or force of tension).
- Force exerted by a spring: The horizontal force exerted by a string when two bodies attached to it are displaced in opposite direction is called restoring force. This force is directly proportional to the displacement of the two bodies.
- Force exerted during collision: When two bodies collide, equal and opposite forces act on each body which make them to move apart after the collision.
- Force applied as a pull or push: When a body is pushed or pulled, it gets displaced.
The forces which act on bodies without being physically touched are called the non-contact forces or the forces at a distance.
- Gravitational force: The force due to pull of gravity(or earth’s attraction ) is called the gravitational force. It causes motion in the body downwards. Example: a ball placed on a table starts rolling down when the table is tilted, if a body is thrown in air, it goes up reaches to a height and then returns to the ground.
- Electrostatic force: The force between the two point charges placed at a separation is called the electrostatic force. Two like charges repel while two unlike charges attract each other.
- Magnetic force: The force between two magnetic poles placed at a separation is called the magnetic force. Two like poles repel while two unlike poles attract each other.
Effects of a force:
- Force can change the state of rest or the state of motion.
- Force can change the speed or the direction of motion or both.
- Force can change the size or shape of the body.