Practice Questions: Force and Energy - Simple Machine

# NCERT Solutions for Class 8 Science - Force and Energy - Simple Machine

Ques 1: What is force?
Ans: A push or pull acting on an object is called force.

Ques 2: What is gravity?
Ans: The force that attracts objects towards the centre of the earth is called gravity.

Ques 3: What is magnetism?
Ans: The push or pull applied by a magnet on metals like iron and nickel and on other magnets is called magnetism.

Ques 4: What is energy? Name any four types of energy.
Ans: The ability to do work is called energy. The four types of energy are heat energy, light energy, wind energy and sound energy.

Ques 5: What is a machine?

Ans: A machine is a tool that makes our work easier by helping us overcome a larger force (load) by applying a lesser force (effort).

Ques 6: Name the six types of simple machines.
Ans: The six types of simple machines are:

1. Lever
2. Pulley
3. Wheel and axle
4. Wedge
5. Screw
6. Inclined plane

Ques 7: List the four effects that force has on objects.
Ans: The four effects that force have on objects are:

1. A force can make a stationary object move or make a moving object move faster.
2. A force can make a moving object stop or slow down.
3. A force can change the direction in which an object is moving.
4. A force can change the shape of an object.

Ques 8: What is friction? Why is friction necessary?
Ans: The force that tries to stop the sliding movement of objects across a surface is called friction. Friction is necessary because friction between our feet and the ground makes it possible for us to walk.

Ans: The two advantages of friction are:

1. The friction between the tyres of vehicles and the road makes them roll forward. Thus, friction makes the movement of vehicles possible.
2. Friction between the chalk and the blackboard makes it possible for the teachers to write on the blackboard.

The two disadvantages of friction are:

1. Friction makes it hard to slide heavy objects across the floor.
2. Friction generates heat. The heat produced due to friction causes damage to machine parts like car brakes.

Ques 10: What is a lever? Describe the three types with examples.
Ans: A lever is a rigid road arranged in such a manner that it can move freely around a fixed point. It consists of the following three parts:

1. Fulcrum: This is the fixed point around which the road moves.
2. Load: It is the object on which work is to be performed.
3. Effort: It is the force that needs to be applied on the road in order to perform a task.

First-class lever:

1. Levers in which the fulcrum is located between the load and effort are called first-class or class-one levers.
2. Eg: a pair of scissors, a seesaw and a crowbar.

Second class lever:

1. Levers in which the load is located between the fulcrum and the effort are called second class or class two levers.
2. Eg: a wheelbarrow, a bottle opener and a nutcracker.

Third class lever:

1. Levers in which the effort is located between the fulcrum and the load are called third class or class three levers.

Ques 11: What is a wheel and axle? Give examples.
Ans: A wheel and axle consists of a wheel rigidly attached to a rod (called an axle). When one rotates the wheel, the axle also rotates.
Eg: The crane used to raise a bucket of water from a well, a screwdriver, a door knob and the steering wheel of a car.

Ques 12: What is a pulley? What are its different types? Give examples.
Ans: A pulley consists of a wheel with a grooved rim, with a rope, chain or belt running around it. The wheel rotates around a stationary axle. A pulley can be of two types fixed and movable.

Fixed pulley:

1. The axle is fixed to some kind of support like a hook or a wall. This pulley changes the destruction of the force and makes the work easier.
2. E.g.: To lift a bucket of water from a well, to raise a flag to the top of a flag holder.

Movable pulley:

1. The axle is not fixed to any kind of support. It is free and movable. This pulley helps to lift heavy loads with less effort. It is usually used in combination with a fixed pulley.
2. Eg: A machine like a crane uses both fixed and movable pulleys to lift heavy loads.

Ans: The two advantages of friction are –

1. The friction between the types of vehicles and the road makes them roll forward. This friction makes as movement of vehicles possible.
2. Friction between chalk and the blackboard makes it possible for the teachers to write on the blackboard.

The two disadvantages of friction are –

1. Friction makes it hard to slide heavy objects across the floor.
2. Friction generates heat. The heat produced due to friction causes damage to machine parts like car brakes.

Ques 14: What is a lever? Describe its three types with examples.
Ans: A lever is a rigid rod arranged in such a manner that it can move freely around a fixed point. It consists of the following three parts.

1. Fulcrum – This is the fixed point around which the rod moves.
2. Load – It is the object on which work is to be performed.
3. Effort – It is the force that needs to be applied to the rod in order to perform a task.

First–Class lever: Levers in which the fulcrum is located between the load and effort are called first-class or class one levers. Eg. – a pair of scissors, a seesaw, and a crowbar.
Second – Class lever: Levers in which the load is located between the fulcrum and the effort are called second-class or class two levers. Eg. – a wheelbarrow, a bottle opener and a nutcracker.
Third–class lever: Levers in which the effort is located between the fulcrum and the load are called third–class three levers. Eg. – Stapler, forceps, fishing rods and ice tongs or chimta.

Ques 15: What is a wheel and axle? Give examples.
Ans: A wheel and axle consists of a wheel rigidly attached to a rod (called an axle). When one rotates the wheel, the axle also rotates. Eg. – The crank used to raise a bucket of water from a well, a screwdriver, a door knob and the steering whole are.

Ques 16: What is a pulley? What are its different types? Give examples
Ans: A pulley consists of a wheel with a grooved rim, with a rope, chain, or belt running around it. The wheel rotates around a stationary axle. A pulley can be of two types fixed and movable.

• Fixed pulley: The axle is fixed to some kind of support like a hook or a well. This pulley changed the direction of the force and made the work easier. Eg.- to lift a bucket of water from a well, to raise a flag to the top of a flagpole.
• Movable pulley: The axle is not fixed to any kind of support. It is free and movable. It is free and movable. This pulley helps to lift heavy loads with less effort. It is usually used in combination with a fixed pulley. Eg. – Machine like a crane uses both fixed and movable pulleys to lift heavy loads.
The document NCERT Solutions for Class 8 Science - Force and Energy - Simple Machine is a part of the Class 5 Course Science Class 5.
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## FAQs on NCERT Solutions for Class 8 Science - Force and Energy - Simple Machine

 1. What are simple machines and how do they relate to force and energy?
Ans. Simple machines are mechanical devices that help in doing work by reducing the amount of force or effort needed. They are used to multiply or change the direction of force, making it easier to perform tasks. Simple machines, such as levers, pulleys, and inclined planes, utilize force and energy to make work more manageable.
 2. How does a lever work as a simple machine?
Ans. A lever is a simple machine that consists of a rigid bar or beam that pivots on a fulcrum. It helps in lifting or moving heavy objects by applying a smaller force over a larger distance. The effort force is applied at one end of the lever, the load is placed at the other end, and the fulcrum acts as the pivot point. By adjusting the position of the load and effort force, the lever allows for the multiplication or change in direction of force.
 3. Can you provide examples of everyday objects that work as simple machines?
Ans. Yes, there are several everyday objects that work as simple machines. Some examples include: 1. Scissors: Scissors work as a lever, with the pivot point acting as the fulcrum. They make cutting easier by increasing the applied force and reducing the effort required. 2. Wheel and axle: This simple machine is present in various objects like a car wheel, a doorknob, or a bicycle. It consists of a wheel attached to a rod or axle, allowing for easy rotation and movement. 3. Ramp: A ramp or inclined plane is a simple machine that allows objects to be moved up or down with less force. It reduces the effort required to lift heavy objects, like a wheelchair ramp or a loading ramp.
 4. How does a pulley function as a simple machine?
Ans. A pulley is a simple machine that consists of a grooved wheel with a rope or chain running along the groove. It is used to lift or move heavy objects by applying a smaller force. The effort force is applied to one end of the rope, while the load is attached to the other end. When the rope is pulled, it moves through the groove, causing the load to move. Pulleys can be combined to create a mechanical advantage, allowing for easier lifting of heavy loads.
 5. What is the relationship between force, work, and energy in the context of simple machines?
Ans. In the context of simple machines, force is the effort applied to perform work. Work is the result of applying force over a distance, and it is the measurement of energy transfer. Simple machines help in reducing the amount of force required to perform work. By utilizing mechanical advantage, they allow for the same amount of work to be done with less force or effort. Therefore, simple machines help conserve energy by making tasks easier to accomplish.

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