1.Force
A. Force is a push or a pull. It is an external cause which changes or tends to change the state of rest or motion
i) Force can change the shape of an object.
ii) Force can change the speed of motion
iii) Force can change the direction of motion. iv) Force can change the state of motion or rest.
2. Give two examples each for a contact force and a force at a distance.(2M) (AS 1)
A. Contact force: Force is being applied by actually touching the body is called contact
force.
Eg:1) Muscular force i) Frictional force.
Non contact force (or) Force at a distance: Force is being applied without touching the body is called non contact force or force at a distance.
Eg: i) Gravitational force, is) Magnetic force, is) Electrostatic force. 3. Explain Gravitational Force by giving a suitable example. (4M) (AS 1) A. Definition: The force exerted on a vertically projected body by earth is called gravitational force. Because of this force only the body falls down
Explanation:
to the ground.
1. Every object on the earth or close to earth will experience a gravitational pull. 2. This force of attraction exists between two bodies everywhere in the universe. 3. Since earth is having more mass all the bodies which are close to the earth are attracted towards it.
4. We cannot experience the gravitational force that exists between two persons and person with any table or black board because it is very small
Eg :
1) The force between teacher and student in the classroom
2) The force between student and black board.
3) The force between Earth and Moon.
4) The force between any two heavenly bodies.
4. Draw and explain a free body diagram (FBD) to show all the forces acting on (4 M) (AS 5)
a car.
A. Here Force
F = Applied by the Engine.
f = Frictional force applied by the road.
N1 and N2 are Normal forces
W= Weight of the car or Gravitational force.
The Net resultant force in vertical direction
Fnet= N1 + N2 - W
The Net resultant force along Horizontal force.
fnet = F-f
5. Why do tools meant for cutting always have sharp edges? (2M) (AS 1)
A. The effect of force depends on the area of contact on which the force is When there is a decrease in the area of contact of the force or load then the effect of force increases and vice versa. So the tools meant for cutting always have sharp edges to acquire maximum effect of force.
1. How can you differentiate between a contact force and a force at a distance?
(2M) (AS 1)
Contact force
1. Force is being applied by actually touching the body
Eg: Muscular force, Frictional force
Force at distance
1. Force is being applied without touching the body.
. Eg: Gravitational force, Magnetic force
3. A man stand still on a level floor. What forces will act on him? Draw a free body diagram (FBD) to show all forces acting on him. (2M) (AS 5)
A. Two forces acting on a man standing on a level floor
W - Weight (Gravitational force)
N - Normal force.
4. The surface area of an object is 20 m? and a force of 10N is applied on it, then what is the pressure ? (2M) (AS 7)
A. Pressure Force = 10 N
Area = 20 m
Pressure = Force/Area
P = 0.5 N/m or Pascal.
5. How do you appreciate the role of friction in facilitating our various activities? (2M) (AS 6)
A. If there is no friction between any two surfaces in contact, then the present day civilization will be no more as we cannot even walk properly on the ground. There will be no fabrics and garment, no construction of buildings and no future, even no fire for cooking and no vehicles. So friction is very necessary in our daily life. So, I appreciate the friction for its facilitation to us for doing various activities in our daily life.
Higher Order Thinking Questions
1. If you push a heavy box which is rest, you must exert some force to start its motion. However, once the box is sliding, you apply a lesser force to maintain that motion. Why?(2M) (AS 1)
A. When a heavy box is at rest there is maximum frictional force between box and surface. So maximum force is used to move that box. Interlocking of irregularities in the two surfaces which are in contact cause friction force. When the box starts sliding, the static friction converts into sliding friction, which is less than static friction. So we need smaller force to maintain that motion
2. Karthik is observing the live telecast of a one day cricket match. He noticed that motion of a roller on the pitch during lunch break. He thought about various forces acting on the roller and the net force when it is in motion. Many questions arose in his mind regarding the direction of the net force. Can you guess what would be those questions? (2M) (AS 2)
A. I think the following questions will be raised in his mind regarding the direction of the net force of the moving roller.
i Why does the roller move when it is pushed ? ii. What is the net force acting on the roller when it was pushed ?
iii. What are the forces acting on the roller when it moves ?
iv. Does the motion of the roller depend on the roughness and smoothness of the ground or not ?
3. Imagine that friction disappeared from the earth. What will happen? Explain. (2M) (AS 2)
A. If the friction has disappeared from the earth,motion
i. We will not be able to walk or run on the ground.
ii. Vehicles will not move if they are in rest. Vehicles will not stop if they are in
iii. We will not be able to hold the things.
iv. Accidents will occur if there is no friction. v. Without friction no building could be constructed.
 (AS 1) A. Force is a push or a pull. It is an external cause which chang...){kind=link}
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