Force and Types of force.

Question 1:

Choose the term to fill in the blanks.
(a) ...... has to be applied to change the ..... of a ...... object.
(moving, direction, force)
(b) When an elephant drags a wooden log over the land, the forces that are applied on the log are ...... , ....... and ........ .
(muscular force, mechanical force, gravitational force, frictional force)
(c) A ball was set rolling on a large table. If its ...... is to be changed, a ........ will have to be applied on it.
(force, motion, gravitation)
(d) The force of friction always acts ........ the motion.
(along, against)

ANSWER:

(a) Force has to be applied to change the direction of a moving object.
(b) When an elephant drags a wooden log over the land, the forces that are applied on the log are muscular force , gravitational force and frictional force.
(c) A ball was set rolling on a large table. If its motion is to be changed, a force will have to be applied on it.
(d) The force of friction always acts against the motion.

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Question 2:

Match the following :

Group ‘A’	Group ‘B’
(i) An ox pulling a cart	(a) Magnetic force
(ii) Lifting a heavy iron object with a crane	(b) Electrostatic force
(iii) Weighing with a spring balance	(c) Muscular force
(iv) Applying brakes to a bicycle	(d) Gravitational force
(v) Picking up pieces of paper with a plastic scale	(e) Frictional force

ANSWER:

Group ‘A’	Group ‘B’
(i) An ox pulling a cart	(c) Muscular force
(ii) Lifting a heavy iron object with a crane	(a) Magnetic force
(iii) Weighing with a spring balance	(d) Gravitational force
(iv) Applying brakes to a bicycle	(e) Frictional force
(v) Picking up pieces of paper with a plastic scale	(b) Electrostatic force

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Question 3:

One or more forces are acting in the following examples. Name them.
(a) An object falling from a tall building ....
(b) An aeroplane flying in sky ....
(c) Squeezing sugarcane juice with a squeezer ........ .
(d) Winnowing foodgrain ....... .

ANSWER:

(a) An object falling from a tall building: Gravitational force
(b) An aeroplane flying in sky: Mechanical and Gravitational force
(c) Squeezing sugarcane juice with a squeezer: Muscular force
(d) Winnowing foodgrain: Muscular and Gravitational force

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Question 4:

Explain in your own words giving one example each.
Muscular force, gravitational force, mechanical force, electrostatic force, the force of friction and magnetic force.

ANSWER:

Muscular force: The force applied by the action of muscles in our body is termed as a muscular force. For example, when you pick up a book placed on the table using your hands, you apply muscular force.

Gravitational force: It is the force that is exerted by the Earth on every object, which is near or on its surface. For example, an apple falling from a tree branch towards the ground is due to gravitational force.

Mechanical force: The force generated by the means of a machine is known as mechanical force. For example, when a car gets started, its engine creates a mechanical force on the tyres that help the car to accelerate. So here, the movement of car occurs due to the force generated by the machine on the tyres.

Electrostatic force: Electrostatic force is the force that exists either between the two charged bodies, or between a charged and an uncharged body. For example, the charged scale attracts the pieces of paper by a non-contact force known as electrostatic force.

The force of friction: The force which acts opposite to the direction of motion of a body is known as the force of friction. For example, a ball rolling on a ground stops after sometime because of frictional force acting between the ground and the ball.

Magnetic force: The force exerted by a magnet is known as magnetic force. For example, separation of iron stuffs from junk is done with the help of magnetic force.

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Question 5:

Why ?
(a) Machines are oiled from time to time.
(b) An object thrown upwards comes down after reaching a point.
(c) Powder is sprinkled on a carrom board.
(d) The ramp at a railway station has a rough surface.

ANSWER:

(a) A machine is oiled from time to time to reduce friction between its body parts. By doing so, life span of a machine increases.

(b) An object thrown upwards comes down after reaching a point. This is because of the Earth's gravitational pull.

(c) Powder is sprinkled on a carom board to reduce friction between the striker/carom coins and the carom board. The powder smoothens the surface of the board and thus the striker and coins can move on it easily.

(d) The ramp at a railway station has a rough surface so that the friction between our feet and the ground is enough for us to walk comfortably and without tripping.

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Question 6:

In what way are we different?
(a) Muscular force and mechanical force.
(b) The force of friction and gravitational force.

ANSWER:

(a) 

Muscular force	Mechanical force
The force applied by the action of muscles in our body is termed as a muscular force.	The force generated by the means of a machine is known as mechanical force.
For example, when you pick up a book placed on the table using your hands, you apply muscular force.	For example, when a car gets started, its engine creates a mechanical force on the tyres that help the car to accelerate. So here, the movement of car occurs due to the force generated by the machine on the tyres.

(b) 

The force of friction	Gravitational force
The force which acts opposite to the direction of motion of a body is known as the force of friction.	It is the force that is exerted by the earth on every object, which is near or on its surface.
It is a contact type of force.	It is non-contact type of force.
For example, a ball rolling on a ground stops after sometime because of frictional force acting between the ground and the ball.	For example, an apple falling from a tree branch towards the ground is due to gravitational force.

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Question 7:

Write answers to the following questions in your own words.
(a) What are the things that can be done by applying force?
(b) What is meant by weight?
(c) Which machines run on muscular force?

ANSWER:

(a) Following things can be done by applying force:

(i) It can move a body initially at rest.

(ii) It can bring a moving body to rest.

(iii) It can change the direction of a moving body.

(iv) It can change the speed of a moving body.

(v) It can change the shape of a body.

(vi) It can change the size of a body.

(b) Weight is the force exerted on a body due to the gravitational pull of Earth.

(c) Machines which run on muscular force are:

• Bicycle
• Rickshaw
• Hand pump
• Stitching machine
• Hand cart

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Question 8:

Solve the following crossword puzzle.

Down :
(1) ....... force is to be applied to push a scooter that has failed.
(2) ........... force can be used to pick up scattered pins.
Across :
(1) A .......... pulls an iron nail towards itself.
(3) .......... force was used when the farm was ploughed with a tractor.
(4) It is due to the force of ............ that raindrops fall to the ground

ANSWER: