Question 1.
Give two examples each of the situations in which you push or pull to change the state of motion of objects.
(i) Push: We close drawer by pushing.
We move a wooden box by pushing.
(ii) Pull: We draw water from a well by pulling the rope.
A horse pulls a cart.
Question 2.
Give two examples of situations in which applied force causes a change in the shape of an object.
When we apply force on a rubber band to stretch it and on clay to change its shape.
Question 3.
Fill in the blanks in the following statements.
(a) To draw water from a well we have to ______ at the rope.
(b) A charged body ______ an uncharged body towards it.
(c) To move a loaded trolley we have to ______ it.
(d) The north pole of a magnet _______ the north pole of another magnet.
(a) pull
(b) attracts
(c) push
(d) repels
Question 4.
An archer stretches her bow while taking aim at the target. She then releases the arrow, which begins to move towards the target. Based on this information fill up the gaps in the following statements using the following terms:
muscular, contact, non-contact, gravity, friction, shape, attraction
(a) To stretch the bow, the archer applies a force that causes a change in its ______
(b) The force applied by the archer to stretch the bow is an example of ______ force.
(c) The type of force responsible for a change in the state of motion of the arrow is an example of a ______ force.
(d) While the arrow moves towards its target, the forces acting on it are due to _______ and that due to _____ of air.
(a) shape
(b) muscular
(c) contact
(d) gravity, friction
Question 5.
In the following situations identify the agent exerting the force and the object on which it acts. State the effect of the force in each case.
(a) Squeezing a piece of lemon between the fingers to extract its juice.
(b) Taking out paste from a toothpaste tube.
(c) A load suspended from a spring while its other end is on a hook fixed to a wall.
(d) An athlete making a high jump to clear the bar at a certain height.
(a) Agents are fingers, object is lemon, effect of force changes the shape of lemon.
(b) Agents are fingers of the person squeezing the tube, object is toothpaste tube and effect of the force can be observed as the paste coming out of the tube (change in shape).
(c) Agent is the load suspended, object is the spring and effort can be seen in the form of elongation of spring on suspension of load (change in shape).
(d) Agent is muscles of athlete, object is athlete himself and effect of the force changes the state of motion of the athlete.
Question 6.
A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?
The force due to hammering causes the change in the shape of the iron and iron can be moulded in the shape of the required tool.
Question 7.
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?
Electrostatic force.
Question 8.
Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion.
Forces acting on bucket are as follows:
(i) Muscular force of arms acting upward.
(ii) Force of gravity acting downward.
Both the forces do not bring any change in the state of motion because both of them are acting in equal and opposite directions and thus they cancel each other’s effect.
Question 9.
A rocket has been fired upwards to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.
The forces that act when a rocket leaves launching pad are as follows:
(i) Gravitational force of the earth (downward)
(ii) Frictional force of air (in opposite direction)
Question 10.
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 rubber bulb
(d) atmospheric pressure
(d) atmospheric pressure
Table 11.1 gives some examples of familiar situations involving the motion of objects. You can add more such situations or replace those given here. Try to identify action involved in each case as a push and/or a pull and record your observations. One example has been given to help you.
Identifying Actions as Push or Pull
Question 11.
When we press the bulb of a dropper with its nozzle kept in water, air in the dropper seems 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
- pressure of water
- gravity of the earth.
- shape of rubber bulb.
- atmospheric pressure.
atmospheric pressure
Question 12.
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 ?
Electrostatic force.
Question 13.
Define force.
Force is a push or pull on an object.
Question 14.
How many objects should be present for a force to come into play ?
There should be atleast two objects for a force to come into play.
Question 15.
Two friends A and B are applying a force of 2 newton and 4 newton on a box in the same direction. What will be the total force applied by them ?
The total force will be 6 newton, i.e., the sum of their individual forces.
Question 16.
In a tug of war, side A applies 10 newton force and side B applies 8 newton force. Which side will the rope move ?
The rope will move towards side A as more force is applied by side A.
Question 17.
What happens to the speed of a body when a force is applied ?
The speed of a body can be increased or decreased by applying force.
Question 18.
Can we change the direction of the moving object by applying a force ?
Yes, we can change the direction of the moving object by applying a force.
Question 19.
What is meant by change in state of motion of the object ?
Any change in the speed or direction of motion or both means a change in state of motion of the object.
Question 20.
Is it possible that a force changes the direction of motion but not the speed of an object ?
Yes, it is possible when a body is moving on a circular path.
Question 21.
Give an example to show that force can change the shape of an object.
Pressing a rubber ball with the hand changes its shape
Question 22.
What is meant by muscular force ?
The force resulting due to the action of muscles is known” as the muscular force.
Question 23.
What is meant by contact force ?
A force which is applied only when it is in contact with an object is called a contact force.
Question 24.
Does the force of friction also act on the objects moving in the air ?
Yes, air also offers friction to objects moving in air.
Question 25.
Is it essential for the agent applying a force on an object to be in contact ?
No, the force can also act from a distance. It is known as non-contact force.
Question 26.
Give one example of a force which can act from a distance.
Magnetic force, i.e., the force exerted by a magnet on another magnet or a piece of iron.
Question 27.
What is meant by force of gravitation ?
The force of attraction exerted by the earth on all objects is called the force of gravitation.
Question 28.
Is the force of gravity a contact force or non-contact force ?
Force of gravity is a non-contact force.
Question 29.
Which force is responsible for the weight of objects ?.
The force of gravity is responsible for the weight of objects.
Question 30.
Does the force of gravitation exist between two objects on the earth ?
Yes, the force of gravitation exists between two objects on the earth but it is very weak.
Question 31.
Do the gases and liquids exert pressure on the walls of the container ?
Yes, liquids and gases exert pressure on the walls of the container.
Question 32.
Define atmosphere.
The air surrounding us is known as atmosphere.
Question 33.
Name two types of contact forces.
Muscular force and frictional force.
Question 34.
Name the force due to which planets revolve around the sun.
Gravitational force.
Question 35.
Why is it comfortable to lift a school bag with broad straps than thin straps ?
Pressure is inversely proportional to area. Since broader straps have greater area, therefore, the pressure decreases.
Question 36.
Why do mountaineers suffer from nose bleeding at high altitudes ?
The atmospheric pressure decreases with high altitude. Since the pressure of the blood inside the body is high, the nose starts bleeding.
Question 37.
Why is easier to hammer a sharp nail into wood than a blunt one ?
Pressure = force / area.
Therefore, when we hammer a sharp nail, force acts on a smaller area, and it exerts more pressure on the nail.
Question 38.
How would pressure change if
- area is doubled keeping force constant
- force is doubled keeping area constant ?
- If area is doubled keeping the force constant, then pressure becomes half.
- If force is doubled keeping area constant, then pressure becomes double.
Question 39.
Why are caterpillar tracks used in battle tanks instead of tyres ?
Caterpillar tracks are used in battle tanks instead of tyres to increase the area of contact. As a result they can even cross sinking grounds as the pressure exerted on the ground is less.
Question 40.
Give two examples each of situations in which you push or pull to change the state of motion of objects.
Push — moving a loaded cart, batsman hitting a ball.
Pull — opening a drawer, drawing a bucket of water from a well.