Newton's laws of motion
Newton's laws of motion
Newton has given three laws to describe the motion of bodies. These laws are known as Newton's laws of motion. The Newton's laws of motion give a precise definition of force and establish a relationship between the force applied on a body and the state of motion acquired by it.
Newton's first law of motion -
Newton's first law describes the behaviour of such bodies which are in a state of rest or of uniform motion in a straight line.
According to Newton's first law of motion -
A body at rest will remain at rest, and a body in motion will continue in motion in a straight line with a uniform speed, unless it is compelled by an external force to change its state of rest or of uniform motion.
It should be noted that by saying an external force, we mean a force from outside the body.
Let us take some examples to make the first law of motion more clear.
Suppose a book is lying on the table. It is at rest. The book will not move by itself, that is,it cannot change its position of rest by itself. It can change its state of rest only when compelled by the force of our hands,that is , when we lift the book from the table. Thus, the position of rest of the book has been changed by the external force of our hands. And this observation supports the first law of motion.
The tendency of a body to remain at rest ( stationary) or, if moving, to continue moving in a straight line,i i called inertia. Newton's first law recognizes that every body has some inertia. Inertia is that property of a body due to which it resists a change in its rest or of uniform motion. Greater the inertia of a body, greater will be the force required to bring a change in its state of rest or of uniform motion. In fact, mass is a measure of the inertia of a body. So the heavier objects have more inertia than lighter objects.
For example, a stone has greater inertia than a football. If we kick a stone, it will not move because of its high inertia but if we kick a football,it will move a long way.
Newton's second law of motion -
Newton's second law of motion in terms of momentum can be started as the rate of change of momentum of a body with respect to time is directly proportional to the net external force acting on the body and takes place in the direction of force.
Suppose a body of mass m is acted upon by an unbalanced external force F which creates an acceleration a in the body. Let the initial velocity of the body be u . Let the force continues to act for a time interval t and the final velocity of the body be v . Then according to Newton's second law -
Change in momentum
Force ~ -----------------------------------
Time
mv - mu
F ~ -------------------------
t
m ( v - u )
F ~ -------------------
t
F ~ ma
F = kma
The value of k is 1 .
Therefore, F = ma
The S.I. unit of force is Newton (N) .
Newton's third law of motion -
Newton's third law of motion states that -
In any interaction between two bodies, the force applied by the first body on the second is equal and opposite to the force applied by the second body on the first.
This means that forces always occur in pairs.
For example - If we hit a wall with our fist, the wall also hits our fist with the same force, which our fist feel.
Newton has given three laws to describe the motion of bodies. These laws are known as Newton's laws of motion. The Newton's laws of motion give a precise definition of force and establish a relationship between the force applied on a body and the state of motion acquired by it.
Newton's first law of motion -
Newton's first law describes the behaviour of such bodies which are in a state of rest or of uniform motion in a straight line.
According to Newton's first law of motion -
A body at rest will remain at rest, and a body in motion will continue in motion in a straight line with a uniform speed, unless it is compelled by an external force to change its state of rest or of uniform motion.
It should be noted that by saying an external force, we mean a force from outside the body.
Let us take some examples to make the first law of motion more clear.
Suppose a book is lying on the table. It is at rest. The book will not move by itself, that is,it cannot change its position of rest by itself. It can change its state of rest only when compelled by the force of our hands,that is , when we lift the book from the table. Thus, the position of rest of the book has been changed by the external force of our hands. And this observation supports the first law of motion.
The tendency of a body to remain at rest ( stationary) or, if moving, to continue moving in a straight line,i i called inertia. Newton's first law recognizes that every body has some inertia. Inertia is that property of a body due to which it resists a change in its rest or of uniform motion. Greater the inertia of a body, greater will be the force required to bring a change in its state of rest or of uniform motion. In fact, mass is a measure of the inertia of a body. So the heavier objects have more inertia than lighter objects.
For example, a stone has greater inertia than a football. If we kick a stone, it will not move because of its high inertia but if we kick a football,it will move a long way.
Newton's second law of motion -
Newton's second law of motion in terms of momentum can be started as the rate of change of momentum of a body with respect to time is directly proportional to the net external force acting on the body and takes place in the direction of force.
Suppose a body of mass m is acted upon by an unbalanced external force F which creates an acceleration a in the body. Let the initial velocity of the body be u . Let the force continues to act for a time interval t and the final velocity of the body be v . Then according to Newton's second law -
Change in momentum
Force ~ -----------------------------------
Time
mv - mu
F ~ -------------------------
t
m ( v - u )
F ~ -------------------
t
F ~ ma
F = kma
The value of k is 1 .
Therefore, F = ma
The S.I. unit of force is Newton (N) .
Newton's third law of motion -
Newton's third law of motion states that -
In any interaction between two bodies, the force applied by the first body on the second is equal and opposite to the force applied by the second body on the first.
This means that forces always occur in pairs.
For example - If we hit a wall with our fist, the wall also hits our fist with the same force, which our fist feel.
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