|History & Civics|
1) Give two examples of each of the situation in which you push or pull to change the state of motion of objects.
(i) We push a bicycle to move it.
(ii) We pull the table to change its position.
2) Give two examples of situations in which applied force causes a change in the shape of an object.
(i) When we press the foam, its shape is changed.
(ii) When we stretch the rubber band, then its shape is changed.
3) In the following situations identify the agent exerting a force and the object on which it acts. State the effect of 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) The fingers are the agents, lemon is the object. The effect of force is the lemon juice expelled by squeezing.
(b) The hand is the agent, toothpaste tube is object and the coming out of paste from toothpaste tube is the effect of force.
(c) Suspended load is agent, spring is the object, the effect of force can be seen in the form of elongation of spring on suspension of load.
(d) Athlete is the agent, bar is the object. The force can be seen in the form of jump.
4) 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 shape of iron and iron can be moulded in the shape of the required tool.
5) 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.
Muscular and gravitational forces act on plastic bucket. The force acting on the bucket do not bring a change in state of motion because they are acting in opposite direction with equal magnitudes. Therefore the net force on bucket remains zero.
6) A rocket has been fired upward to launch a satellite in its orbit. Name the two forces acting on the rocket immediately after leaving the launching pad.
(i) Gravitational force
(ii) Force of friction.
7) What will be the resultant force when two forces act in opposite directions on an object?
When two forces act in opposite directions on an object then, the net force will be the difference between two forces.
8) Why does force of friction called contact force?
Since the force of friction arises due to contact between surfaces of moving body and surfaces, it is called contact force.
A contact force is a force that acts at the point of contact between two objects, in contrast to body forces.
9) What is a force? Explain with the help of some examples.
Force is a pull or push of the objects. The action like, pushing, pulling, picking, hitting, lifting, running and bending are the examples of force. Moving or stopping of a body, changing shape and direction of motion of objects are various actions which show force in play.
10) How do we feel force in our daily life?
Various big or small actions make us feel the force. We hit or catch many objects in our daily life. We see that a moving ball stops of its own. The ball changes the direction of its motion when hit with a bat. These are many actions which help us to feel that a force is exerted.
11) Explain that forces are due to an interaction between objects.
Imagine, a man is standing behind a stationary car. The car does not move due to his presence. Now allow the man to push the car, it means, he applies a force on the car. The car may begin to move in the direction of the applied force. Note that the man has to push the car to make it move. This example shows that at least two objects must interact for a force to come into action.
12) What happen's when
(i) Two forces are exerted in same direction?
(ii) Two forces are exerted in opposite directions?
(i) When two forces are exerted in same direction on an object, then the forces are added and action becomes easy.
(ii) When two forces act in the opposite directions on an object, the net force acting on it is the difference between the two forces.
13) What are the two factors which affect the effect of changes?
These are following two factors which affect the effect of changes.
(i) Magnitude: The strength of force is usually expressed by its magnitude.
(ii) Direction of force: We have also to specify the direction of force in which the force acts.If the direction or magnitude of force changes, its effect also changes.
14) What are the effects of force?
A force changes or try to change the
(i) Speed of a moving body.
(ii) Direction of motion of a body.
(iii) Shape of a body.
15) Describe state of motion.
There are two states of motion . An object can be in two positions, one is at rest or other in motion. Any change in this position (in rest or motion) can be called the change in the state of motion.