Q.9: Define centrifugal force? Give two examples?
Ans: The force which is directed away from the centre of circle is called centrifugal force. It is an opposite and equal reaction of centripetal forces.
F = ———————-
- When a stone at the end of string to keep the stone in circular motion acting force pulls it inward along the string.
- According to third law of motion if stone reacts and exerts an equal force outward on the hand. The outward force on the hand is called centrifugal force.
Q.9: What is banking of a road? What is its advantages?
Ans: The outer edges of the curved roads are made higher than the inner edges. This is called banking of the road.
Advantage Of Banking Of A Road:
When the vehicle exceeds a certain limit, turning a corner the centnpetal force is unable to keep the vehicle moving in a circle and the vehicle tends to skit away from the center. The banker road keeps the vehicle moving safely around the curve. The speed limits are mentioned around the curves on the roads for safe driving.
Q.10: Define Centrifuge? Give some its applications?
It is a device which separates heavier particles from lighter particles in a liquid. A centrifuge is cylindrical vessel in which a liquid is rotated at a high speed by an electric motor.
Application Of A Centrifuge:
- Wet clothes are rotated at a high speed in washing machine dryers. The wall of the dryers have numerous holes. When the dryer runs, water separates from the clothes by centrifugal force and goes out side from the holes and clothes are dried up.
- Sugar crystals are separated from the molasses by centrifuges.
- A cream separator also acts as a centrifuge. The cream collects near the axis and the skimmed milk moves away from the axis of rotation.
Q.16: What is a satellite? What are natural and artificial satellites?
An object revolving around a planet in a fixed orbit is called a satellite. There are two kinds of satellite.
They exist naturally and revolve round the planets. Like moon which moves round the earth.
The satellite sent by the scientists which move round the earth are called artificial satellite. They are sent for different purposes like telecommunication, space research, etc.
Q.18: Is it possible for a body to be accelerated if its speed is constant?
Ans: Yes, it is possible. If a body is moving with constant velocity but changes its direction then it will have acceleration. A body moving with a uniform speed in a circle has acceleration. The centripetal force always acts at right angle to the instantaneous velocity of the object Therefore the centripetal force can not change the magnitude of the velocity. However the force changes the direction of the velocity, therefore it has acceleration.
Q.19: Why is the acceleration of a body moving uniformly in a circle direction towards the center?
Ans: According to Newton’s Second Law of Motion, acceleration is always produced in the direction of force. The force acting on a body moving uniformly in a circle is always directed towards the center of the circle. This force is called the centripetal force. Centripetal means center seeking. Therefore the acceleration of a body moving uniformly in a circle is also directed towards the center.
Q.20: When a moving car turns round a corner to the left, in which direction the occupants tend to fail?
Ans: We know that a force is required to keep an object moving in a circle as this force is always directed towards the center it is called centripetal force (center seeking force) While a car is turning round a corner the centripetal force is provided by the friction between the road and tires. When a car takes a turn to the left, the occupants along with the car tend to fall to the right. If the road is slippery or if the tires of the car are worn out there might be insufficient centripetal force and the car might skid to the left. For safety the centripetal force might be provided by making the outer edge of a curved road a little higher than the inner edge. This is called banking of the road. Thus the car can move safely on banked roads at prescribed speed limits.