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1. Define Force.
A force is an influence which tends to set a stationary body in motion or which tends to change the speed and direction of a moving body or which tends to change the shape of a body.
2. What are the differences between contact force and non-contact force?
A force that can be applied only when it is in contact with an object is called a contact force.
Example : Muscular force, frictional force.
A force that can be applied without any contact between two bodies is called non-contact force.
Example : Magnetic force, Gravitational force.
3. Auto rickshaw moves when pushed from outside. But it doesn't move if pushing from inside. Why?
An unbalanced external force alone can make a body move. Push from inside is not an unbalanced external force, it can not move the auto rickshaw.
4. State Newton's First Law of Motion.
Every body continues in its state of rest or of uniform motion along a straight line until it is acted upon by an external unbalanced force.
5. What is meant by inertia?
Inertia is the tendency of a body to continue in its state of rest of the state of uniform motion along a straight line.
6. A person travels in a cycle moves for some distance even after he stop the pedal. Why?
Even after stopping the pedal the cycle moves some distance due to the inertia of motion of cycle. But it comes to rest due to the frictional force applied by the floor.
7. Athletes run some distance before making a long jump. What is the reason?
It is done for utilizing the motion due to inertia. Velocity acquired by them when they are running will help to leap a long distance.
8.When an elephant chases people escape by running through a zig-zag road. Why?
Here people takes the advantages of the inertia of motion of the elephant. Due to inertia elephant with its huge body can not move along a zig-zag path.
9. What happens to the passengers travelling in a bus when the bus takes a sharp turn? Give reasons for your answer.
When the bus turns a corner sharply, we tend to move sideways because of our inertia or tendency to continue moving in a straight line.
10. What all changes can force make on a body?
i) It can change the size and shape of the body.
ii) It can change the state of rest of the body.
iii) It can change the speed of a moving body along with its direction of motion.
11. If we want to move forward on a ground in which direction should the force be applied, forward or backward?
When we want to move forward, we exert a backward force on the ground. Then the ground will exert a force in the opposite direction on our foot. So we are able to move forward.
12. What are the significances of the first law of the motion?
i) The first part of the law defines inertia.
ii) The second part of the law defines force.
13. A passenger is standing inside a running bus. The bus stops all of a sudden. What will happen to him? Why?
The passenger falls forwards. When the bus stops suddenly the foot of the passenger comes to rest. But his body continues to move forwards. Hence he fall forwards. This is an example of inertia of motion.
14. What will happen when a stationary bus suddenly moves forward? From these examples, what inferences can we arrive at?
When the stationary bus suddenly moves forward, a standing passenger falls backwards. This is an example of inertia of rest. The feet suddenly moves forward but the body continues in its state of rest.
15. A person shakes one branch of a mango tree while trying to pluck some mangoes. Some mangoes get separated and fall off. What is the principle behind this?
The branch was at a state of rest at the initial stage. When the person shakes the branch it attains some motion. But the mangoes try to continue in the state of rest as they are heavy. Due to this inertia of rest the mangoes fall off.
16. An electric fan was rotating. Even after switching off the fan it continues to rotate for sometime. Explain the reason?
It is an example of inertia of motion. Objects that are in motion do not have the capacity to stop suddenly. This is the reason why an electric fan continues to rotate even after switching off the fan.
17. What is the cause of friction?
Friction is caused by the roughness of the surfaces in contact. Even smooth looking surfaces in contact. Even smooth looking surfaces have hills and valleys. This will be evident if you observe them using a microscope. These hills have valleys of the two surfaces interlock causing friction.
18. Big buildings have broad basements. Give the reason.
Surface area increases when the basement of the buildings are broad.
19. What is standard atmospheric pressure?
Atmospheric pressure at the sea level is equal to the pressure exerted by 0.76m if mercury column. This is standard atmospheric pressure.
20. To clean a carpet we usually beat it with a stick. Why?
On striking, the carpet suddenly moves. The dust particles have a tendency too remain at rest due to its inertia. Thus the dust particles get separated from the carpet.
