# Force and Pressure

## Extra Questions

Question 1: What do you understand by state of motion?

Answer: A force can change the state of motion. Both rest and motion are called states of motion. When an object is at rest, its speed is zero.

Question 2: Explain friction.

Answer: When one surface is moving over another surface, a force comes into play and opposes their relative motion. This force is called friction or force of friction. Friction always opposes motion because it acts in opposite direction to motion. Force of friction arises due to contact between two surfaces. If there is not contact between two surfaces there would be no friction.

Question 3: Why is it easier to push a nail in a wooden plank through its pointed end?

Answer: It is easier to push a nail into a wooden door through its pointed end than through its blunt end, because small area of the pointed end helps in creating more pressure and it becomes easier to insert the nail.

Question 4: What is the difference between contact and non-contact forces?

Contact forceNon-contact force
This force needs to touch the object in order to exert its effect.This force does not need to touch the object in order to exert its effect.
Example: muscular force, frictionExample: magnetic force, electrostatic force

Question 5: Two tyres of a tractor are very wide and huge. Why?

Answer: A wide tyre means larger area. We know that pressure reduces when area increases. The wide tyres reduce the pressure affected by tractor. As a result, it becomes easier to drive a tractor on a muddy surface or on a freshly ploughed surface.

Question 6: A camel can easily walk on sand but a man finds it difficult. Why?

Answer: Camel’s feet are wide; making for larger area. Due to this, a camel can easily walk on sand.

Question 7: It is easier to cut an apple with sharp end of knife rather than with its blunt end. Why?

Answer: The sharp end of knife has much smaller area compared to its blunt end. Smaller area provides more pressure for the applied force. Hence, it becomes easier to cut an apple with sharp end of knife compared to with its blunt end.

Question 8: Why do Eskimos wear ski-like shoes?

Answer: Eskimos wear ski-like footwear. Wider area of the footwear reduces pressure and thus prevents the Eskimo’s feet from sinking in ice.

Question 1: Explain some characteristics of force.

Answer: Following are some characteristics of force:

• At least two objects need to interact for force to come into play. Mutual interaction between two objects results in a force between the two objects.
• When two forces are applied on an object in the same direction, there is an add-on effect of both forces.
• When two forces are applied in opposite directions, the difference between two forces gives the value of the net force.
• Force is expressed in terms of its magnitude and the direction in which it is working. Any change in direction or magnitude of the force, there is a change in effect of the force.
• Generally, more than one force is acting on an object at any given time.

Question 2: What are the effects of force on a moving object?

Answer: A force can have following effects on a moving object.

• When the applied force is in the same direction as direction of motion, there is an increase in the speed of object.
• When the applied force is in opposite direction of motion, there is a decrease in the speed of object. The object may also come to rest when the applied force is in opposite direction to the direction of motion.
• When the applied force is at some acute or obtuse angle to the direction of motion, there is a change in the direction of motion.

Question 3: What are the effects of force on shape of an object?

Answer: Force can change the shape of an object. When force is applied on a ball of dough, there is a change in the shape of dough. Similarly, a potter changes a lump of clay into pots by applying force. When air is filled in a balloon; the shape of the balloon changes because of the applied force.

Question 4: How do liquids and gases exert pressure?

Answer: Liquids and gases exert pressure as follows:

• Pressure at the bottom of container depends on the height of column of gas or liquid. Due to this, divers have to withstand a large pressure at the bottom of the sea.
• A fluid exerts pressure on walls of the container. Containers for gases and liquids are usually cylindrical ion shape to equally distribute the pressure on all portions of the wall.
• A fluid exerts equal pressure at same depth.