Lakhmir Singh & Manjit Kaur: Force and Pressure- 1 | Lakhmir Singh & Manjit Kaur Solutions: Class 8 Science PDF Download

Q.1. What is the push or pull on an object known as? 

Force is a Pull or a push on the object.

Q.2. Why do the shape and size of a balloon change when filled with air or water?

As we know that air and water are the matter and matter has a characteristic property which says that they have mass and occupy certain space. So when air or water is filled in a balloon, they tend to stretch its rubber boundary and occupy the space. Therefore the shape and size of the balloon get change when filled with air or water.

Q.3. Name the quantity whose unit is ‘Newton’ (N).

Force
The unit of force is Newton. Kg ms^-2 = Newton

Q.4. When a ball is dropped from a height, its speed increases gradually. Name the force which causes this change in speed.

Gravitational force
Every object in the universal exerts a force on every other object. this force is known as the gravitational force.

Q.5. What is the unit of force? 

Newton
The unit of force is Newton

Q.6. Give one example where force changes the shape of an object. 

When you squeeze a toothpaste.
Force can change the shape, size, direction, etc on applying the body.

Q.7. Identify the actions involved in the following situations as push or pull, or both:
(a) Opening a drawer.
(b) A cricket ball hit by a batsman.
(c) Drawing a bucket of water from a well.
(d) moving a book placed on a table.
(e) A football player taking a penalty corner.
(f) Moving a wheel barrow.

(a) PULL
Force is a Pull or a push on the object.
(b) PUSH
Force is a Pull or a push on the object.
(c) PULL
Force is a Pull or a push on the object.
(d) Ans
Both push and pull Pull or push on an object is known as force
(e) Push
Pull or push on an object is known as force
(f) Push
Pull or push on an object is known as force.

Q.8.
(A) Name two contact forces.

• Frictional force
• Applied force

The force applied when it is in contact with the object.

(B) Name two non-contact forces.

• Gravitational force.
• Magnetic force.

The force acting on an object without being in contact with it is known as non-contact force.

Q.9. When a plastic pen is rubbed in dry hair, it attracts tiny pieces of paper. Which force is involved in this process?

Electrostatic force due to create unlike charge by rubbing to get attracted

Q.10. A small device pulls iron nails from a distance. Which type of force is involved in this process?

Magnetic force
Iron nails get attracted by magnet without touching them.

Q.11. Which force can be used to gather iron pins scattered on the floor?

Magnetic force
Iron pins get attracted by magnet without touching them.

Q.12. Name the force which always opposes motion.

Friction force acting between the two surfaces in the contact with each other which oppose the motion

Q.13. Which force makes a rolling ball stop on its own?

Friction force acting between the two surfaces in the contact with each other which oppose the motion, due to which stop the moving object.

Q.14. An inflated balloon was pressed against a wall after it has been rubbed with a piece of synthetic cloth. It was found that the balloon sticks to the wall. What force might be responsible for the attraction between the balloon and the wall?

Electrostatic force
On the rubbing an object to get charged (static charge) and unlike charges get attracted to each other, such type of force is Electrostatic force.

Q.15. What name is given to the force acting on a unit area of an object? 

Pressure
Pressure = thrust (force) / area

Q.16. Name the quantity whose one of the units is Pascal (Pa)?

Pressure
The unit of pressure is Pascal (Pa).

Q.17. What conclusion do you get from the observation that a fountain of water is created at the leaking joint of pipes of the main water supply line?

Water exerts force on the bottom of the container.

Q.18. What type of pressure is involved in the filling of a liquid in a syringe?

Air pressure
Pressure = thrust (force)/area

Q.19. What substance present in our body balances the atmospheric pressure acting on us?

Our Blood (Internal body pressure created by blood)

Q.20. Where will the atmospheric pressure be greater-at ground level or at the top of high mountain?

Ground Level
At mountain air is low.

Q.21. Name any two devices used in everyday life which work on the existence of atmospheric pressure.

• Drinking Straw works on atmospheric pressure
• Vacuum Cleaner works on atmospheric pressure.

Q.22. If a vacuum is created between two Magdeburg hemispheres joined together, they cannot be separated easily, What presses the hemispheres together?

The two hemispheres pressed together when vacuum is created between them because air is pumped out of the interior which create the remarkable force between them to stick together.

Q.23. What makes a balloon get inflated when air is filled in it?

When we filled air in the balloon, the inside pressure in the balloon increases and thereby the surface area of balloon increases. Thus the force acting by air molecule inside outward and the force acting by air from outside inward equals. This balancing force tend to make a balloon get inflated when air is filled in it.

Q.24. Name the substance whose weight produces atmospheric pressure.

Air has mass and occupied space.

Q.25. Where is the pressure greater, 10m below the surface of the sea or 20m below the surface of sea?

20m below the surface of sea.
Pressure increases with height or depth of sea level

Q.26. What force acting on, an area of 0.5 m² will produce a pressure of 500 Pa?

250N
P = F/A
F = P × A
= 500 × 0.5 = 250 N

Q.27. Can a liquid exert pressure upwards?

Yes, but exert more pressure downwards than upwards.

Q.28. Can a liquid exert pressure sideways? 

Yes, Liquid exert pressure in all direction.

Q.29. State whether the following statements are true or false:
(a) The pressure exerted by a liquid depends on the area of base of its container.
(b) A drinking straw works on the pressure exerted by the liquid filled in a soft drink bottle in which it is placed.

(a) True
Pressure depends on the area and force.
(b) False
Pressure depends on the area and force.

Q.30. Fill in the following blanks with suitable words:
(a) To draw water ‘from a well, we have to ________ at the rope.
(b) If the two forces applied to an object are equal and act in opposite directions, the net force acting on the object will be ________
(c) Force could be a ________ or a ________
(d) Force has magnitude as well as ________
(e) A force arises due to ________ between two objects.
(f) A charged body ________ an uncharged body towards it.
(g) The north pole of a magnet ________ the north pole of another magnet.
(h) Force acting on a unit area is called ________
(i) The pressure exerted by a liquid ________ with depth.
(J) A drinking straw works on the existence of ________ pressure.
(k) Atmospheric pressure ________ with increasing height.

(a) To draw water ‘from a well, we have to apply pull force at the rope.

To draw an object by applying force
(b) If the two forces applied to an object are equal and act in opposite directions, the net force acting on the object will be zero.

The force applied on the body are equal and opposite direction, force cancel out and net force is zero.
(c) Force could be a push or a pull.

A push or pull on an object is known as force.
(d) Force has magnitude as well as direction.

Force is a vector quantity and it depends on direction.
(e) A force arises due to interaction between two objects.
The interaction between two objects due to a force .
(f) A charged body attracts an uncharged body towards it.
Force attracts to each other of two objects when they are unlike charges.
(g) The north pole of a magnet repeals the north pole of another magnet.
Like poles of magnet repeal to each other’s.
(h) Force acting on a unit area is called Pressure.
(i) The pressure exerted by a liquid increases with depth.
Pressure = height × density of object × gravity
(J) A drinking straw works on the existence of atmospheric pressure.
The level of water rises from drinking straw due to atmospheric pressure.
(k) Atmospheric pressure decreases with increasing height.
Pressure is inversely proportional to height