Lakhmir singh solutions science class 8 Solutions for Chapter 11 force and pressure

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

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

Name the quantity whose unit is Newton.

What is the direction of force of friction acting on a moving object?

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

What is the unit of force?

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

Identify the actions involved in the following situations as a 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 wheelbarrow.

a) Name two contact forces.

b) Name two non-contact forces

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

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

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

Name the force which opposes the motion.

Which force makes a rolling ball stop on its own?

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?

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

Name the quantity whose one of the units is Pascal?

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?

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

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

Where will the atmospheric pressure be greater: at ground level or at the top of a high mountain?

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

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

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

Name the substance whose weight produces atmospheric pressure.

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

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

Can a liquid exert pressure upwards?

Can a liquid exert pressure sideways?

State whether the following statements are true or false:

a) The pressure exerted by a liquid depends on the area of the 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.

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) The 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 unchanged 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.

Define ‘state of motion’ of an object. Name the agent which can change the state of motion of an object.

Give two examples of situations where you push or pull to change the state of motion of objects.

What is meant by saying that force is due to an interaction? Give an example to illustrate your answer.

In a tug of war, when the two teams are pulling the rope, a stage comes when the rope does not move to either side at all. What can you say about the magnitudes and directions of the forces being applied to the rope by the two teams at this stage?

What is a force? State the various effects of force.

a) Give one example where force moves a stationary object.

b) State one example where force stops a moving object.

a) Give one example where force changes the speed of a moving object.

b) Give one example where force changes the direction of a moving object.

Why does the shape of an ointment tube change when we squeeze it?

What happens to the springs of a sofa when we sit on it?

Name the various types of forces.

What is the muscular force? Give one example of muscular force.

Which of the following are non-contact forces? Magnetic force, frictional force, gravitational force, muscular force, electrostatic force.

Give two examples from everyday life which show that air exerts pressure.

What is a rubber sucker? How does it work? State any one use of a rubber sucker.

Why do mountaineers usually suffer from nose-bleeding at high altitude?

Describe one activity to show the existence of atmospheric pressure.

Explain why water comes out more slowly from an upstairs tap than from a similar tap downstairs.

What is meant by gravitational force? Give its example.

Calculate the pressure when a force of 200N is exerted on an area of

a) 10 m^2

b) 5 m^2

Which force do the animals apply while moving, chewing, and doing other activities?

Which force is responsible for raising our body hair when we try to take off a terylene or polyester shirt in the dry weather?

Name the type of forces involved in the following:

a) A horse pulling a cart.

b) A sticker attached to steel almirah without glue.

c) A coin falling to the ground on slipping from hand.

d) A plastic comb rubbed in dry hair picking up tiny pieces of paper.

e) A moving boat coming to rest when rowing is stopped.

Why does a sharp knife cut objects more effectively than a blunt knife?

Explain why wooden sleepers are kept below the railway line.

Explain why a wide steel belt is provided over the wheels of an army tank.

Explain why the tip of a sewing needle is sharp.

Explain why snowshoes stop you from sinking into the snow.

Explain why when a person stands on a cushion, the depression is much more than when he lies down on it.

Explain why porters place a thick round piece of cloth on their heads when they have to carry heavy loads.

Give one practical application of magnetic force.

a) What is meant by a contact force? Explain with the help of an example.

b) What is meant by a non-contact force? Explain with the help of an example.

a) Define the frictional force.

b) Explain why the frictional force is said to be a contact force.

a) Define pressure. What are the relation between pressure, force, and area? State the units in which pressure is measured.

b) Explain why school bags are provided with wide straps to carry them?

a) What is meant by atmospheric pressure? What is the cause of atmospheric pressure?

b) Why are our bodies not crushed by the large pressure exerted by the atmosphere?

c) Explain why atmospheric pressure decreases as we go higher up above the earth’s surface.

a) How does the pressure of a liquid depend on its depth? Draw a labelled diagram to show that the pressure of a liquid depends on its depth.

b) Explain why the walls of a dam are thicker near the bottom than at the top.

Which of the following is not an example of muscular force?

a) A porter carrying a load on a wheelbarrow.

b) An apple falling from a tree.

c) A child riding a bicycle.

d) A person drawing water from a well.

Which of the following is not an example of the force of gravity?

a) a leaf falling from a tree

b) a boy pushing a cart on a level plane

c) a diver jumping into a swimming pool

d) a stone falling from the top of a cliff

When we press the bulb of a dropper with its nozzle kept in water air in the dropper is seen to escape in the form of bubbles. Once we release the pressure on the bulb, water gets filled in the dropper. The rise of water in the dropper is due to:

a) pressure of water

b) gravity of the earth

c) shape of a rubber bulb

d) atmospheric pressure

A rectangular wooden block has length, breadth, and height of 50cm, 25cm, and 10cm respectively. This wooden block is kept on the ground in three different ways, turn by turn. Which of the following is the correct statement about the pressure exerted by this block on the ground?

a) the maximum pressure is exerted when the length and breadth from the base

b) the maximum pressure is exerted when length and height form the base

c) the maximum pressure is exerted when breadth and height form the base

d) the minimum pressure is exerted when length and height form the base

Which of the following is contact force?

i) friction

ii) gravitational force

iii) magnetic force

iv) muscular force

a) i and ii

b) ii and iii

c) i and iv

d) ii and iv

If we release a magnet held in our hand, it falls to the ground. The force responsible for this is:

a) muscular force

b) magnetic force

c) electrostatic force

d) gravitational force

Which of the following force is utilized in reducing air pollution by removing dust, soot, and fly-ash particles from the smoke coming out of chimneys of factories?

a) magnetic force

b) gravitational force

c) electrostatic force

d) frictional force

The same force facts on four different objects having the areas given below, one by one. In which case the pressure exerted will be the maximum?

a) 20 m^2

b) 50 m^2

c) 10 m^2

d) 100 m^2

Which of the following represent correct values for the normal atmospheric pressure?

i) 101.3 kPa

ii) 76 mm of mercury

iii) 101.3 Pa

iv) 76 cm of mercury

a) i and ii

b) ii and iii

c) i and iv

d) ii and iv

Which of the following does not work on the existence of atmospheric pressure?

a) rise of iodine solution in the glass tube of dropper

b) rise of cold drink in a long plastic straw

c) sticking of suction hook on the wall of a room

d) rise of mercury in a glass tube of a thermometer

The magnitude of the force is expressed in the unit of force called:

a) pascal

b) kelvin

c) newton

d) Magdeburg

Which of the following change appreciably when a batsman hits a moving cricket ball?

i) shape

ii) direction

iii) size

iv) speed

a) i and ii

b) ii and iii

c) i and iii

d) ii and iv

Which of the following is not an effect of force?

a) a force can change the speed of a moving object

b) a force can change the direction of a moving object

c) a force can change the composition of a moving object

d) a force can change the shape and size of an object

Which of the following is not a non-contact force?

a) electrostatic force

b) gravitational force

c) frictional force

d) magnetic force

Which of the following scientists gave the idea of the existence of gravitational force?

a) Einstein

b) James Watt

c) Faraday

d) Newton

Some mustard oil is kept in a beaker. It will exert pressure:

a) downwards only

b) sideways only

c) upwards only

d) in all directions

A pressure of 10 kPa acts on an area of 0.3m2. The force acting on the area will be:

a) 3000 N

b) 30 N

c) 3 N

d) 300 N

The magnitude of atmospheric pressure is equal to the pressure exerted by a:

a) 76 mm tall column of mercury

b) 760 mm tall column of alcohol

c) 76 cm tall column of mercury

d) 760 cm tall column of mercury

The atmospheric pressure is usually measured in the unit of:

a) Newtons per square meter

b) Pascal

c) cm of mercury

d) mm of mercury

When a force of 5N acts on a surface, it produces a pressure of 500 Pa. The area of the surface then must be

a) 10 cm^2

b) 50 cm^2

c) 100 cm^2

d) 0.01 cm^2