Newton’s first law of motion and inertia
In this topic we will discuss about Newton’s first law of motion and inertia . Force , linear momentum and some example of inertia (all type).
Newton’s first law of motion ( law of inertia )-
Before to know the Newton’s first law of motion and inertia we must know –
FORCE– Force is a physical quantity which when applied on a body it actually changes or try to change , shape, size and, position of rest or motion.
INERTIA – It is the property of a body by virtue of which it can’t change itself its state of rest or uniform motion in a straight line . Or we can say ‘inertia is the resistance of change’. this term inertia is first used by Galileo .
Different types of inertia –
- Inertia of rest – It is the tendency of a body to remain in its position of rest .
Example- A person standing in a bus fall backward when the bus suddenly start moving forward. Dust is removed from a hanging carpet by beating it with a stick, etc.
- Inertia of motion– It is the tendency of a body to remain in its state of uniform motion in a straight line .
Example-When a running bus stop suddenly the passengers in the bus fall in forward direction. It is dangerous to jump out from a running bus, etc.
- Inertia of direction– It is the property of the body to restrict the change of direction of motion.
Example- When a bus takes a sharp turn the person sitting in the bus experiences a force acting away from the centre of the curved path .
Linear momentum (momentum) – momentum of a body is the quantity of motion possessed by the body . Mathematically it is equal to the product of mass and velocity of the body .
If ‘m’ is the mass of the body and its velocity is’v’ then it is given momentum P = m v .
It is a vector quantity .
Its unit is kg m/s or Ns.
And its dimension is [M L T-1] .
Newton’s first law of motion – It is also known as law of inertia. According to Newton’s first law of motion ‘every body remain in its position of rest or of uniform motion in a straight line , till no external force acts on it’ .
This law consist of three parts ;
(i) firs part say a body is in rest continues in the states of rest( inertia of rest).
(ii) second part say that body is in motion continue moves in the same path with same speed (inertia of motion)
(iii)third part say that if a body moving with wit uniform velocity in a st. line then it cant change its direction of motion it self ( inertia of direction ) .
From the above three parts given above explain that how Newton’s first law explain the law of inertia.
Illustration of Newton’s first law of motion –
- Based on inertia of rest-
(i) When we shake a branch of tree its fruit and dry leaves fall down – It is because when we shake the tree its branches comes in motion but due to inertia of rest fruit or leaves wants to be in rest due to which it separated from the branches of tree and fall down.
(ii) When a horse suddenly start running then the riders on it fall back -It is because initially the rider and horse are in rest , when horse starts running suddenly the part of the rider in contact with the horse comes into the motion but upper part of the body due to inertia in rest remain in rest and the rider falls back.
(iii) A person standing in a bus fall backward when the bus suddenly start moving suddenly forward- -It is because initially the person and bus are in rest , when bus starts moving suddenly the part of the person in contact with the bus comes into the motion but upper part of the body due to inertia in rest remain in rest and the person falls back.
(iv) Dust is removed from a hanging carpet by beating it with a stick- it is because when we hit the carpet it comes in motion but due to inertia of rest dust wants to be in rest due to which it separated from the carpet and fall down.
2.Based on inertia of motion–
(i) When a running bus stop suddenly the passengers in the bus fall in forward direction.- It is because when the bus is in motion then the passenger on it also is in motion , but when bus stop suddenly then the portion of the passenger is in contact with the bus also comes in rest but due to inertia of motion upper part of the passenger remain in motion and hence passengers fall in forward direction or in the direction of the moving bus .
(ii) It is dangerous to jump out from a running bus – .- It is because when the bus is in motion then the passenger on it also is in motion , but when the person jumps out then the lower part of the body comes in contact with the ground and it comes in rest but due to inertia of motion upper portion of the body remain in motion and person fall down in the direction of motion of bus and it becomes the cause of accident.
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