Q1: Give two examples each of situations in which you push or pull to change the state of motion of objects?
Answer:
A goal keeper saving a goal.
Hockey player flicking a ball.
Q2: What is a force?
Answer:
Force is a push or a pull acting on an object which changes or tends to change the state of the object.
Actions like pulling, pushing, lifting, kicking, opening etc. are tasks we generally do in our daily life. These actions often result in change in position of the object. We say an effort is required either to push or pull an object, this effort is called force.
The SI (International System of Units) unit of force is Newton
Q3: Give two examples of situations in which applied force causes a change in the shape of an object.
Answer:
a. A lump of dough on a plate.
b. A rubber band suspended from a hook.
Q4: Fill in the blanks in the following statements:
Answer:
(a) To draw water from a well we have to pull (force) at the rope.
(b) A charged body attracts an uncharged body towards it.
(c) To move a loaded trolley we have to push it.
(d) The north pole of a magnet repels the north pole of another magnet.
Q5: 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
Answer:
(a) To stretch the bow, the archer applies a force that causes a change in its shape.
(b) The force applied by the archer to stretch the bow is an example of muscular force.
(c) The type of force responsible for a change in the state of motion of the arrow is an example of a contact force.
(d) While the arrow moves towards its target, the forces acting on it are due to gravity and that due to friction of air.
Q6: A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?
Answer: The force due to hammering changes the shape of the piece of iron.
Q7: What force can do?
Answer: When a force is applied on an object, it:can move an object from rest. can change the speed of an object if it is moving. can change the direction of motion of an object. can bring about a change in the shape of an object. may or may not cause any of these or all of these effects
Q8: 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?
Answer: The force which is responsible for the attraction between the ball and the wall is electrostatic force. When we rub the balloon by a synthetic cloth, it gets charged. When it is taken near the wall, it will get attracted towards the uncharged wall because of the electrostatic force which is the force exerted by a charged body on another uncharged body.
Q9: 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.
Answer: The force acting on a plastic bucket containing water held above the ground level are :
1. Gravitational force: It is acting downwards.
2. Muscular force: It is applied by our hands to lift the bucket in upward direction.
Although these forces are acting on the bucket but no change is found in its state of motion because the forces are balancing each other and as a result net force becomes zero.
Q10: 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.
Answer: Two forces acting on the rocket immediately after leaving the launching pad are:
1. Frictional force due to air,
2. Force of gravity pulling in downward direction.
Answer:
A goal keeper saving a goal.
Hockey player flicking a ball.
Q2: What is a force?
Answer:
Force is a push or a pull acting on an object which changes or tends to change the state of the object.
Actions like pulling, pushing, lifting, kicking, opening etc. are tasks we generally do in our daily life. These actions often result in change in position of the object. We say an effort is required either to push or pull an object, this effort is called force.
The SI (International System of Units) unit of force is Newton
Q3: Give two examples of situations in which applied force causes a change in the shape of an object.
Answer:
a. A lump of dough on a plate.
b. A rubber band suspended from a hook.
Q4: Fill in the blanks in the following statements:
Answer:
(a) To draw water from a well we have to pull (force) at the rope.
(b) A charged body attracts an uncharged body towards it.
(c) To move a loaded trolley we have to push it.
(d) The north pole of a magnet repels the north pole of another magnet.
Q5: 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
Answer:
(a) To stretch the bow, the archer applies a force that causes a change in its shape.
(b) The force applied by the archer to stretch the bow is an example of muscular force.
(c) The type of force responsible for a change in the state of motion of the arrow is an example of a contact force.
(d) While the arrow moves towards its target, the forces acting on it are due to gravity and that due to friction of air.
Q6: A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?
Answer: The force due to hammering changes the shape of the piece of iron.
Q7: What force can do?
Answer: When a force is applied on an object, it:can move an object from rest. can change the speed of an object if it is moving. can change the direction of motion of an object. can bring about a change in the shape of an object. may or may not cause any of these or all of these effects
Q8: 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?
Answer: The force which is responsible for the attraction between the ball and the wall is electrostatic force. When we rub the balloon by a synthetic cloth, it gets charged. When it is taken near the wall, it will get attracted towards the uncharged wall because of the electrostatic force which is the force exerted by a charged body on another uncharged body.
Q9: 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.
Answer: The force acting on a plastic bucket containing water held above the ground level are :
1. Gravitational force: It is acting downwards.
2. Muscular force: It is applied by our hands to lift the bucket in upward direction.
Although these forces are acting on the bucket but no change is found in its state of motion because the forces are balancing each other and as a result net force becomes zero.
Q10: 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.
Answer: Two forces acting on the rocket immediately after leaving the launching pad are:
1. Frictional force due to air,
2. Force of gravity pulling in downward direction.
Q11: Why does hair of the hand raise when the hand is brought near to television screen once the TV is switch1d off?
Answer: The television screen becomes electrically charged and it exerts an electrostatic force on the hair of your hand. This force is a non-contact force because, there is no contact between the screen and the hair.
Q12: Define Pressure.
Answer: The force acting per unit surface area is called pressure. The SI unit of pressure is measured in newton/metre2, which is equal to 1 pascal (Pa).
Pressure = Force / Area
Q13: How do fluids exert pressure?
Answer: Fluids exert pressure in all directions. Fluids exert pressure on all bodies immersed in them and also on the walls of the container that holds them.
Q14: Suppose your writing desk is tilted a little. A book kept on it starts sliding down. Show the direction of frictional force acting on it.
Answer: Frictional force acts opposite to the movement of the book i.e. upward direction.
Q15: You spill a bucket of soapy water on a marble floor accidentally. Would it make it easier or more difficult for you to walk on the floor? Why?
Answer: It would be difficult to walk on the floor. Soapy water fills the floor irregularities, thus reduces the friction considerably. Feet do not make necessary grip with the floor surface, thus increasing the chances of falling.
Q16: What are the causes of frictions?
Answer: Following are the causes of friction:
1. roughness of two surfaces in contact and interlocking of the irregularities between the surfaces.
2. nature of surface i.e. smooth or rough
3. shape of surface (e.g. flat or curved)
4. impurities between surface (e.g. adding lubricant between two rough surface decrease friction)
5. pressure of two surfaces i.e. how hard the two surfaces are pressed together.
6. mass of the body of surfaces in contact
Q17: Explain why sportsmen use shoes with spikes.
Answer: Spikes increase friction and give tighter grip with ground. It avoids slipping of sportsmen while playing or running.
Q18: Iqbal has to push a lighter box and Veena has to push a similar heavier box on the same floor. Who will have to apply a larger force and why?
Answer: Friction is a self-adjusting force. Increase in weight will put more force on the floor surface and therefore will experience more opposite force (friction). Veena will have to apply larger force.
Q19: Give examples to show that friction is both a friend and a foe.
Answer: Friction is a necessary evil acting both as friend and foe.
Examples of friction as friend:
We are able to walk because of frictional forces between ground and our feet.
We are able to write because of friction between ball point and the paper surface.
Nails and screws stick to wall surfaces because of friction.
Lighting a match stick is because of friction between match stick and the side surface of match box.
Examples of friction as foe:
Wear and tear of soles of our shoes is due to friction.
When a tyre deflates, it is difficult to move the the vehicle because of increased friction between the tyre and road surface.
Machines gets heated up and produce noise because of friction.
Due to friction, machines and vehicles consumes more fuel and increase maintenance cost.
Q20: What is the relation between Force and interaction?
Answer: Whenever there is an interaction between two objects, there is a force acting upon each of the objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction.
Answer: Whenever there is an interaction between two objects, there is a force acting upon each of the objects. When the interaction ceases, the two objects no longer experience the force. Forces only exist as a result of an interaction.
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