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Question 1

What happens when the two forces act in the opposite on an object?
 
 
Solution:
If the two forces act in the opposite direction on an object, the net force acting on it is the difference between the two forces.

Question 2

What is muscular force? Why it is called a contact force?

Solution:
Muscular Force: The force resulting due to the action of muscles is known as muscular force. Since muscular force can be applied only when it is in contact with an object, it is also called a contact force.

 

Question 3

Name some non-contact forces.

Solution:
(i) Electrostatic forces

(ii) Magnetic force

(iii) Force due to gravity.
 

Question 4

How does an applied force changes the speed of an object?

 

Solution:
When a force is applied on an object, it may change its speed. If the applied force is in the direction of motion, the speed of the object increases. If the force is applied in the direction opposite to the motion, then it results in a decrease in the speed of the object.

 

Question 5

What do you know by the state of motion?

Solution:
The state of motion of an object is described by its speed and the direction of motion. The state of rest is considered to be the state of zero speed. An object may be at rest or in motion; both are its state of motion. Any change in the speed, or direction of motion, or both, implies a change in the state of motion of the object.

 

Question 6

We know that there is a huge amount of atmospheric pressure on us. But we do not experience its effect why?

Solution:
We know that air is present everywhere. The pressure of air inside our body is same as that of the atmosphere. Therefore, we do not experience its effect.

 

Question 7

We know that a force applied on an object causes either a change in its state of motion or its shape. Different types of events are listed is the following table. Tell the type of effect in each case.
 
Description of Situation How to apply Force Action of force
Change in state of motion Change in shape
Yes No Yes No
A lump of dough on a plate Pressing it down with hand        
A foam cushion placed on a chair or a bed Pressing with a hand or standing on it.        
A rubber ball placed on a table Pressing it down with hand        
A ball of cotton or a piece of sponge placed on a table By keeping a book or a weight over it        
Spring fixed to the seat of a bicycle By sitting on the seat        
A rubber band suspended from a hook/nail fixed on a wall By hanging a weight or by pulling its free end        
A plastic or metal scale placed between two bricks By putting a weight at the centre of the scale        

 
 

Solution:
 
Description of Situation How to apply Force Action of force
Change in state of motion Change in shape
Yes No Yes No
A lump of dough on a plate Pressing it down with hand   ü ü  
A foam cushion placed on a chair or a bed Pressing with a hand or standing on it.   ü ü  
A rubber ball placed on a table Pressing it down with hand   ü ü  
A ball of cotton or a piece of sponge placed on a table By keeping a book or a weight over it   ü ü  
Spring fixed to the seat of a bicycle By sitting on the seat   ü ü  
A rubber band suspended from a hook/nail fixed on a wall By hanging a weight or by pulling its free end   ü ü  
A plastic or metal scale placed between two bricks By putting a weight at the centre of the scale   ü ü  

Question 8

Why is air not felt?

Solution:
As already mentioned, we are living at the bottom of a sea of air. The atmospheric pressure in the SI units is roughly 100000 newtons/metre2. Now the atmospheric pressure acts on all bodies on the earth's surface. An average-sized person has roughly an area of 2 m2, and so the total thrust acting on our bodies will be about 200000 newton. Yet we don't feel it! This is because the blood and other fluids in our bodies exert pressure slightly greater than the atmospheric pressure and so a balance is obtained. At high altitudes, sometimes, nose bleeding occurs because the atmospheric pressure becomes less than the blood pressure.




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