PHYSICS [2 Mark Question Answer]

The minimum force required to keep the body moving over a surface such that it moves equal distances in equal intervals of time is called the force of sliding friction.

The examples to illustrate that friction is a necessary evil are:

1. If friction were absent, we would not be able to walk.
2. Friction is necessary to burn a matchstick.
3. It is due to friction that we can write on board by chalk.

Disadvantages of friction:

1. Friction produces heat which damages the moving parts of a machine.
2. Friction produces wear and tear on the contacting surfaces. This reduces the life of machine parts, tires and shoe soles.
3. A lot of energy is wasted due to friction to overcome it before moving.

The force of attraction on a body by the earth is called gravitational force.
Example: The leaves and fruits fall from a tree downwards towards the ground, water in a river flows down streams, a ball thrown up goes to a height, and then returns back on the ground are some examples of motion due to gravitational force

Total forces acting downwards = 2 N + 22 N = 24 N
Total forces acting upwards = 8 N + 14 N = 22 N
Resultant force = Difference between the magnitude of forces = 24 N – 22 N = 2 N .
The wooden block will move in the downward direction with the resultant force of 2 N acting on it.

Agent exerting the force is the child himself (muscle of the child). The object on which the force is acting is the child himself. The force is moving the child from a stationary object.

Agent exerting the force is human fingers.
The object on which the force is acting is the medicinal tube. The force is changing the shape of the tube and moving the ointment out of the tube.

Agent exerting the force can be a machine (electric power) or human.
The object on which the force is acting is the orange.
The force is moving the orange and changing the shape of it.

Magnetic force comes into play even when the magnet and other objects (like iron) are kept at a distance and not in direct contact with each other. Hence, magnetic-force is considered as an action-at-a-distance force.

Vehicles slip/skid on muddy and wet roads as the roads become smooth and offer less friction to the tyres. Tyres are therefore grooved or treaded to make their surface rough so that the friction between the tyres and the road increases and vehicles may stop easily when desired.

When we roll an object on a surface, the friction produced between the object and the surface is called rolling friction. Example: when we pull our large suitcases on wheels, rolling friction comes into play. The wheels reduce friction and cut down a lot of effort required to move the suitcase (Rolling friction is less than sliding friction).

It is because when the object is at rest, static friction occurs. The static friction is maximum when the applied force is just short of the force required to start motion between the two bodies in contact. Once the object starts moving, friction (resistance) we feel decreases.