Question 1 What is newton’s third law of motion?
Question 2 Give example of newton’s third law of motion?
Question 3 Which physical principle is involved in the working of a jet aeroplane ?
Question 4 Name the principle on which a rocket works?
Question 5 Why is it difficult to walk on a slippery road?
Question 6 Why a runner presses the ground with his feet before he starts his run?
Question 7 To take the boat away from the bank of a river, the boatman pushes the bank with an oar. Why?
Question 8 Why does a gunman get a jerk on firing a bullet?
Question 9 If action is always equal to reaction, explain why a cart pulled by a horse can be moved?
Newton’s Third Law of Motion
Newton’s third law of motion gives relationship between the forces that come into play when two bodies interact with one another.
Whenever one body exerts a force on another body, the second body exerts an equal and opposite force on first body.
The force exerted by first body is called action.
The force exerted by second body on first body is called reaction.
To every action there is equal and opposite reaction.
1)How do we walk
When we walk on ground, then our feet pushes the ground backward and in return, ground pushes our foot forward. The forward reaction exerted by the ground on our foot makes us walk forward.
If the ground is slippery then it becomes very difficult to walk due to less friction. We cannot exert a backward action force on ground or ice which would produce a forward reaction force on us.
A swimmer pushes the water backward with his hands and feet to move in the forward direction in water. It is equal and opposite to force which pushes swimmer forward.
Though action and reaction forces are equal in magnitude but they do not produce equal acceleration in the two bodies on which they act.
Acceleration produced will be more in body having less mass whereas the acceleration produced will be less in body having more mass.
2)Why the Gun recoils
When a bullet is fired from a gun, force sending the bullet forward is equal to force sending the gun backward. But due to high mass of gun, it moves only a little distance.
3)The case of boat and ship
a)During the rowing of a boat, the batsman pushes the water backward with oars. The water exerts an equal and opposite push on boat which makes the boat move forward. Harder the boatman pushes back the water with oars, greater is the reaction force exerted by water and faster the boat moves.
b)When a man jumps out of a boat to the bank of the river, the boat moves backward away from him.
To step out boat, the man presses the boat with his foo in backward direction(action).The boat exerts an equal force on man in forward direction(reaction)
c)When a boatman wants to take away from bank of river,he sits in the boat and pushes the river bank with oar:When boatman exerts a force of action on the bank,the bank exerts an equal and opposite force of reaction on the boat.So boat move away from bank.