JK Academy Exercise
1. Choose the term to fill in the blanks.
(a) Force has to be applied to change the direction of a moving object.
(moving, direction, force)
(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.
(muscular force, mechanical force, gravitational force, 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.
(force, motion, gravitation)
(d) The force of friction always acts against the motion. (along, against)
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 |
Ans: 1- c; 2 – a; 3 – d; 4 – e; 5 – b
3. One or more forces are acting in the following examples. Name them.
(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 food grain: Muscular and Gravitational force
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.
Muscular force: The force applied with the help of muscles is called muscular force.
For example: bullocks pulling the cart.
Gravitational force: The force applied by the earth to pull objects towards itself is called gravitational force.
For example, Fruits falling from a tree to the ground.
Mechanical force: The force applied by means of a machine is called mechanical force.
For example: washing machine,
Electrostatic force: Static electricity is produced on materials like rubber, plastic and ebonite due to friction. The force exerted by such electrically charged materials is called electrostatic force.
For example: the charged comb attracts the pieces of paper by electrostatic force.
The force of friction: When two surfaces rub against each other, the force of friction comes into play. It always acts against the direction of motion.
For example: When a brake is applied while riding a bicycle, it stops after running a short distance.
Magnetic force: The force exerted by a magnet is known as magnetic force.
For example: an iron nail attracting a magnet.
5. Why ?
(a) Machines are oiled from time to time.
Ans. A machine is oiled from time to time to reduce friction between its body parts.
(b) An object thrown upwards comes down after reaching a point.
Ans. An object thrown upwards comes down after reaching a point because of gravitational force.
(c) Powder is sprinkled on a carrom board.
Ans. Powder is sprinkled on a carrom board to increase the frictional force between the board and the coins.
(d) The ramp at a railway station has a rough surface.
Ans. The ramp at a railway station has a rough surface to reduce the friction between our shoes and the floor.
6. In what way are we different?
(a)
| Muscular force | Mechanical force |
| The force applied with the help of muscles is called muscular force. | The force applied by means of a machine is called mechanical force. |
| For example: a man carrying a bag of rice. | For example: machines in the factory. |
(b)
| The force of friction | Gravitational force |
| When two surfaces rub against each other, the force of friction comes into play. It always acts against the direction of motion. | The force applied by the earth to pull objects towards itself is called gravitational 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: fruits falling from a tree branch towards the ground. |
7. Write answers to the following questions in your own words.
(a) What are the things that can be done by applying force?
Ans. Following things can be done by applying force:
(i) We can move a body which was at rest.
(ii) We can bring a moving body to rest.
(iii) We can change the direction of a moving body.
(iv) We can change the speed of a moving body.
(v) We can change the shape of an object.
(vi) We can change the size of an object.
(b) What is meant by weight?
Ans. The gravitational force acting on a body is called weight.
(c) Which machines run on muscular force?
Ans. Bicycle, boat, hand cart, sewing machine work on muscular force.
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.
Activity :
Collect more information about the various forces that are used in our day-to-day life.
Make a list of such actions where many forces are applied simultaneously.
Extra Questions
Can you tell?
1. What happens when you hold the two ends of a spring and pull them apart?
Ans. When we hold the two ends of a spring and pull them apart the spring will change its shape. The spring will get stretched and become long.
2. What happens when a blacksmith hammers a red hot piece of iron?
Ans. When a blacksmith hammers a red hot piece of iron, the piece of iron will change it shape and the blacksmith can turn it into the shape he desires.
Use your brain power!
For which tasks in your day-to-day life do you use muscular force?
Ans. In our day to day life we use muscular force while writing, playing, eating, pulling, pushing, throwing, catching, etc.
Why is powder sprinkled on the carrom board while playing carrom?
Ans. Powder is sprinkled on the carrom board while playing carom, to reduce the friction between the carom pieces and the board.
Why do fruits on trees fall to the ground?
Ans. Fruits on trees fall to the ground due to gravitational force. The earth pulls all the objects towards itself.
What difference do you notice in the way the two sacks are lifted – one sack is empty and the other full?
Ans. The gravitational force on the empty sack is less, that is to say, it weighs less. The gravitational force on the bigger sack is greater. In other words the bag weighs more. Greater force must be applied to lift a greater weight.
Which forces are acting upon an aeroplane taking off into the sky?
Ans. The airplane taking off into the sky is acted on by two forces—lift, the upward acting force and weight, or gravity, the downward acting force.
When a carrom piece is flicked lightly, it slides over the carrom board, but stops at a certain distance. A ball rolling over a flat ground stops at a certain distance. Why does this happen?
Ans. The carom piece stops because of the force of friction acting between the piece and the board. Similarly the rolling ball stops because of the force of friction acting between the ground and the ball.
When a brake is applied while riding a bicycle, it stops after running a short distance. How does the brake work? Between which parts is friction produced?
Ans. A bicycle brake reduces the speed of a bicycle or prevents it from moving because of friction between the brake pads and the wheel rims.
Take two pieces of smooth paper and two of sandpaper and rub them against each other. What do you notice?
Ans. The smooth surfaces can be easily rubbed against each other because the force of friction between them is less, while rough surfaces cannot be easily rubbed against each other because the force of friction between them is much greater.
Why is a wooden plank laid down for pulling out a car which is stuck in mud?
Ans. A force of friction is generated between the wheel and the wooden plank laid down under the car. Hence, it can be pulled out from the mud.
Fill in the blanks.
1. Force is required to move an object.
2. Force is used to change the direction of an object in motion, or to stop it.
3. Force is necessary to change the shape an object.
4. The force applied with the help of muscles is called muscular force.
5. Some machines are run by using electricity or fuel are called automatic machines, because a mechanical force is used.
6. The force applied by means of a machine is called mechanical force.
7. The force applied by the earth to pull objects towards itself is called gravitational force.
8. Sir Isaac Newton discovered gravitation in the 17th century.
9. The earth’s gravitational force acts in a direction opposite to that of an object moving upwards. Hence, the speed of that object goes on decreasing till in the end it becomes zero.
10. While falling, the speed of an object goes on increasing all the time due to gravitational force.
11. Greater force must be applied to lift a greater weight.
12. The scale on the spring balance shows the gravitational force acting on the object which is the weight of the object.
13. The gravitational force acting on an object is called the weight of that object.
14. The gravitational force operates between the sun and the planets in the solar system.
15. Because of gravitational force, the planets revolve around the sun.
16. At the same time, gravity also operates between planets and their satellites.
17. The force exerted by a magnet is called magnetic force.
18. When two surfaces rub against each other, the force of friction comes into play.
19. Friction force always acts against the direction of motion.
20. The smooth surfaces can be easily rubbed against each other because the force of friction between them is less.
21. The rough surfaces cannot be easily rubbed against each other because the force of friction between them is much greater.
22. It is possible for us to walk on the ground only because of the force of friction.
23. While walking, if there is no friction, we would slip and fall.
24. We are very likely to slip while walking on an oily or wet floor because of no friction.
25. In short, the force of friction can either be decreased or increased as desired.
26. Static electricity is produced on materials like rubber, plastic and ebonite due to friction.
27. The force exerted by electrically charged materials is called electrostatic force.
28. If a variety of forces act together it is called combined force.
29. Force is necessary for making an object move, to change the direction of motion and also to change the shape of an object.
30. Various types of forces acting on a body are muscular force, mechanical force, gravitational force, magnetic force, frictional force and electrostatic force.