Newton’s First Law of Motion
Newton’s First Laws of Motion { Law of Inertia }- It states that a body continue in its state of rest or of uniform motion until it is comepelled by any external unbalance forces.
This laws is also known as law of inertia.
Inertia is the proerty of a body which cause it to maintain its state of motion or rest.
Unbalanced Forces : When two unequal forces acts on an object and the object change its state then we say that the forces are unbalance.
Unbalance forces can be understood from example of tug of war.
Watch this video.
Newton’s Second Law of Motion
Newton’s Second law of motion: It states that rate of change of momentum is directly proportional to unbalance external force. And change of momentum is in the direction of unbalance force.
Mathematical Derivation:
Initial momentum , Pi = mu
Final momentum , Pf = mv
Change in momentum ,∆ = Pf – Pi
= mv – mu
But we know that rate of change of momentum is directly proportional to the applied unbalanced force.
∴ F ∝ ∆/t
or F ∝ (mv – mu ) / t/
Or F ∝ m. ( v -u )/t
Or F ∝ m. a , Where a= Acceleration
Or F = k. m. a ,
Or F = 1. m. a , In SI system K=1
∴ F = m. a
Newton’s Third Laws of Motion
Newton’s third law : ‘To every action there is an equal and opposite reaction.’
This law can be realised while dropping a ball, hammering a nail , holding a hose pipe of high pressurised water pump , during bicycling etc.
Suppose a man pushes an object with a force F, then the object react to this force with an equal and opposite of that force. That means if the man pushes the object with a force F12 then the object pushes him back with the same force F12 but as it is opposite to the direction of the man’s force therefore it can be represented as -F12 . See the image.
Now we will explain the three case as shown int the video. You can also watch the video.
Case 1 [Hose Pipe]: When a man holds a hose pipe of high speed water rushing out from the pipe. The stream of water jet put an action on the hand of the man. Due to this action the man’s hand pushes backward. Due a contact between pipe and the man’s hand a reaction is produced that helps in holding the pipe.
Case 3 [A man jumping from a Boat]: When a man jumps out from a boat , the boat get pushed back. It is because the the man put an action while jumping out of the boat. The boat in return produce a reaction on the man. As the boat is not fixed this force causes boat to go back. In this proces the man get support while jumping due to the reaction force.
Case 2 [Bicycling]: While bicycling , the wheel of the bicycle exerts a pressure on the ground . This is an action against the ground. At the same time the ground also react with reverse force. This is called reaction. Due to this the man get support while bicycling.