Force and Friction

EFFECTS OF FORCE: Various changes take place when force is applied on a body.

  1. Force can make a stationary body move

  2. Force can increase the speed of a moving object

  3. It can make a moving body stop

  4. It can change the direction of a moving body

  5. It can change the shape of body


CONTACT AND NON-CONTACT FORCES

  1. Contact Force: A force acting between two objects that requires a physical contact between them is called a contact force. Ex. Muscular and Frictional force.

  2. Non-Contact Force: A force acting between two objects that does not require a physical contact between them is called a non-contact force. Ex. Gravitational, Electrostatic, and Magnetic force.


TYPES OF FORCE


  1. Muscular Force: It is the force that is the result of the action of muscles. Ex. Lifting a heavy box needs force applied by our hands and a weightlifters lift the weight with the force applied by their arms.

  2. Gravitational Force; The force of attraction that pulls object towards the surface of the Earth is called Gravitational force. It acts between all objects in the universe. Ex. It causes the planets to revolve around the Sun in their orbits, the force between the Moon, the Earth and the Sun causes the phenomenon of ocean tides.

  3. Electrostatic Force: The force acting between charged particles is called electrostatic force. It can either be a force of attraction or a force of repulsion between two charged particles. The nature of the force depends on the nature of the charges.

  4. Magnetic Force: The force exerted between two magnets or between a magnet and a magnetic material such as iron is called magnetic force. The force can either be repulsive or attractive.


FRICTION

The resistive force acting between the bodies that are in contact and in motion such that it opposes the motion is called friction or frictional force. Therefore, friction is a contact force.


TYPES OF FRICTION

  1. Static Friction: The friction acting between two surfaces in contact when there is no relative motion between them is called static friction.

  2. Kinetic Friction: The friction acting between two surfaces in contact when there is relative motion between them is called kinetic friction.

a) The friction acting between the surfaces when an object slides over a surface is called sliding friction.

b) The friction acting between the surfaces when an object rolls over a surface is called rolling friction.


ADVANTAGES OF FRICTION

  1. When we walk on a surface, the friction provided by the surface helps us to walk. Icy roads are very smooth and cannot provide sufficient friction to our feet. So, we find it difficult to walk on an icy road.

  2. We are able to hold objects on our hand because of the friction between out palm and the object. Without friction, the objects would slip off from our hands.

  3. Friction between pulleys of a motor and the belt helps to transfer energy from the motor to the required equipment.

  4. When brakes are applied, friction between the brake pad and the brake disc helps to reduce the speed of vehicle.


DISADVANTAGE OF FRICTION: Friction causes unnecessary wastage of energy and reduces the efficiency of the machines.


METHODS TO MINIMIZE FRICTION: It is necessary to reduce friction in order to increase efficiency, save energy and to protect machines from wear and tear.

  1. Smoothening reduces the roughness on the two surfaces and further reduces the interlocking between the irregularities, thus decreasing the friction.

  2. Oils, grease, graphite powder, etc., when applied between the two surfaces, help the surfaces to slide easily over one another, minimizing the interlocking of the irregularities on the surfaces. Such materials used to reduce friction are called lubricants.

  3. Rolling friction is less than sliding friction. Ball bearings are used to minimize the friction by this method to provide the rolling effect.

  4. Friction caused due to sir (drag) can be reduced by making the object (vehicles) in the desired streamlined shape.

We can see that the streamlined body of living things helps them reduce friction. The shape of a fish helps it to swim easily in water. The shape of a bird minimizes air drag and helps it fly easily.


METHODS TO INCREASE FRICTION

  1. Increasing the roughness of the surface.

  2. Increasing the mass of the object in motion.

EXAMPLES FROM EVERYDAY LIFE:

  1. Tyres of vehicles are treaded to provide sufficient friction between the tyres and the roads.

  2. Trekking shoes have spikes to give strong grip.

  3. Handles of Cricket bats and Badminton and Tennis rackets are made of rough materials for a strong grip.

  4. Playgrounds are made rough so that people would not slip while running or playing.