Science In Everyday Life Solutions for Class 8 Science Chapter 10 Force And Friction are provided here with simple step-by-step explanations. These solutions for Force And Friction are extremely popular among class 8 students for Science Force And Friction Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Science In Everyday Life Book of class 8 Science Chapter 10 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Science In Everyday Life Solutions. All Science In Everyday Life Solutions for class 8 Science are prepared by experts and are 100% accurate.

Page No 147:

Question 1:

Write down any two effects of force.

Answer:

Force can cause a stationary object to move or make a moving object move even faster. Force can slow down or completely stop a moving object.
Force can change the shape and/or size of an object.

Page No 147:

Question 2:

Name any two non-contact forces.

Answer:

Gravitational force and electrostatic force are non-contact forces.

Page No 147:

Question 1:

Write one word for the following.

1. SI unit of force ....................
2. The force with which the Earth pulls us ....................
3. The force between electrical charges ....................
4. A force that attracts iron and nickel objects ....................

Answer:

  1. Newton (N)
  2. Gravitational force
  3. Electrostatic force
  4. Magnetic force

Page No 147:

Question 2:

Define/Explain the following.
1. Force
2. Non-contact forces
3. Contact forces
4. Fluid friction

Answer:

  1. Force is the push or pull that acts on an object to change its state of motion or its shape and/or size.
  2. Non-contact forces are those forces that do not require physical contact between the objects among which they act.
  3. Contact forces are those that can act on objects only when they are in direct or indirect physical contact.
  4. Fluid friction is the force of friction due to fluids such as air and water.

Page No 147:

Question 1:

Write T for the true statement and F for the false one. Correct the false statement(s).
1. A force can change the shape or size of an object.
2. Gravitational force is a contact force.
3. When we lift a weight in our hands, the force required is provided by the tension of our muscles.
4. Friction is a non-contact force.
5. Wear and tear in machine parts can save fuel and energy.

Answer:

  1. T. A force can change the shape or size of an object.
  2. F. Gravitational force does not require contact.
  3. T. When we lift a weight in our hands, the force required is provided by the tension of our muscles.
  4. F. Friction is a contact force as it requires contact between the two objects.
  5. F. Reducing friction can save energy and fuel, while wear and tear increase energy loss.

Page No 147:

Question 1:

A plastic comb attracts small pieces of paper due to
(a) gravitational force
(b) electrostatic force
(c) magnetic force
(d) all of these

Answer:

(b) electrostatic force
Electrostatic force is the force between electric charges. Plastic comb gets charged and induces equal and opposite charges on the pieces of paper thereby attracting them.

Page No 147:

Question 2:

Frictional forces between two surfaces come into play only when the two surfaces
(a) are far away form each other
(b) are close the each other
(c) are in physical contact
(d) do not touch each other

Answer:

(c) are in physical contact
Frictional force acts only when two surfaces are in contact.

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Question 3:

The disadvantage of friction is that
(a) it causes wear and tear
(b) it can make machine parts heat up
(c) it can result in wastage of energy and fuel
(d) all of these

Answer:

(d) all of these
Friction can cause, wear and tear, heating up of machines and wastage of energy and fuel.

Page No 147:

Question 4:

Oil and grease are common
(a) lubricants
(b) ball bearings
(c) anti-lubricants
(d) all of these

Answer:

(a) Lubricants
Oil and grease provide lubrication.

Page No 147:

Question 5:

To reduce drag, automobiles, ships, and aeroplanes are given
(a) a stylish shape
(b) a streamlined shape
(c) treads
(d) ball bearings

Answer:

(b) Streamlined shape
Streamlined shape is given to automobiles, aeroplanes and ships to reduce drag.



Page No 148:

Question 3:

Give two examples of contact forces.

Answer:

Examples of contact forces are:

  1. Frictional force
  2. Applied force (the force that we use using our body parts)

Page No 148:

Question 4:

Why do tiny bits of paper get attracted when brought close to a plastic pen or comb, which have recently been rubbed?

Answer:

When a plastic pen or comb is rubbed, it gets charged. The charged pen or comb then induces equal and opposite charges on the pieces of paper and attracts them by electrostatic force of attraction.

Page No 148:

Question 5:

Give two methods of reducing friction.

Answer:

Two methods of reducing friction are use of ball bearings and lubrication.

Page No 148:

Question 6:

Write down two methods of increasing friction.

Answer:

Two methods to increase friction are:

  1. Making the surfaces in contact with each other more rough, as roughness increases friction.
  2. Ensuring that the surfaces in contact with each other are completely dry, since water can act as a lubricant.

Page No 148:

Question 1:

Write a note on the types of contact and non-contact forces.

Answer:

The types of non-contact forces are:

  • Gravitational force – It is the force with which objects pull each other. E.g. gravitational force of earth keeps us ground to earth.
  • Electrostatic force – It is the force between electric charges. E.g., On rubbing a plastic comb, bits if paper can stick to it.
  • Magnetic force – It is the force that magnets exert on each other and on metals like iron and nickel. E.g., A magnet attracts iron objects.
The types of contact forces are:
  • Applied forces – These are the forces applied collectively by hands, fingers or legs. E.g., lifting an object.
  • Friction – It is the resistance to movement, when two surfaces in contact move with respect to each other. E.g., sliding of an object over another.

Page No 148:

Question 2:

Differentiate between rolling and sliding friction.

Answer:

Rolling friction Sliding friction
The frictional force offered when rolling an object. The frictional force offered when sliding an object.
Rolling is less difficult as area in contact is lesser. Sliding is more difficult as area of contact between objects is more.
It is smaller than sliding friction. It is greater than rolling friction.

Page No 148:

Question 3:

What are the advantages and disadvantages of friction?

Answer:

Some of the advantages of friction are:

  • It helps us to walk, drive and write.
  • It prevents screws and nails from slipping out of wood or metal surface.
  • Helps in keeping things in place, such as a tied knot or bed sheet remains on the bed.
  • It enables sitting on a chair without sliding down.
Some disadvantages of friction are:
  • It causes heating up of moving parts in machinery and automobiles, which causes wastage of energy and fuel.
  • It causes wear and tear of the moving parts.

Page No 148:

Question 4:

Explain why ball bearings are used and how they are helpful.

Answer:

Ball bearings are used to reduce friction as they can change sliding friction to rolling friction. They are used in machines having moving parts. This is based on the fact that rolling friction is much smaller than sliding friction. They are helpful as balls act as rollers; therefore, small metal balls of stainless steel or brass are placed between moving surfaces that are cylindrical or flat. This helps to reduce friction, thereby reducing the wear and tear or heating up of the moving parts and also saves energy and fuel.

Page No 148:

Question 5:

What do you mean by 'streamlined shape'? How does it help in the motion of vehicles?

Answer:

Streamlined shape is a shape which is in line with stream of flowing water or air. It is a special shape given to automobiles, ships and airplanes to reduce drag. When automobiles, aircraft or ships move, their movement is opposed by fluid friction either due to water in case of ships or due to air. To reduce this drag, vehicles, airplanes and ships are given a special shape, which is the streamlined shape. 



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