Facts about Newton's Laws of Motion

Facts about Newton's Laws of Motion

Issac Newton discovered Laws of Motion.

First Law

Every body continue in its state of rest or uniform motion in a straight line unless compelled by an external unbalanced force.

Second Law

The rate of change of momentum is directly proportional to the external unbalanced force and takes place in the direction of the force.

Third Law

For every action there would be an equal and an opposite reaction.

Equations of Motion

There exists some relation between velocity, acceleration and the time intervals during which we study  the motion of a body. These relations are called equations of motion.

They are:

v =u + at
s = ut + ½at2
2as = v2 – u2

where

v — final velocity
u — initial velocity
t — time interval
a — acceleration
s — displacement

If the position of an object in space changes with time relative to an observer, it is said to be in motion.

Physical quantities are of two types :Scalar and Vector quantities.

Scalar quantities have only magnitude and no direction. eg: Distance, mass, temperature, speed etc.

Vector quantities have both magnitude and direction. eg: Displacement, weight, velocity, acceleration etc.

The actual length of path travelled by a body is called the distance covered by a body.

The shortest distance from the initial to the final position of a body is called displacement of the body. It does not depend on the actual path undertaken by the object.

Speed is the distance travelled by a body in unit time. It is a scalar quantity. Its unit is m/s.
Speed = Distance /Time

Velocity is the displacement per unit time. It is a vector quantity and its unit is m/s.
Velocity = Displacement/Time

Acceleration is the rate of change of velocity. It is a vector quantity and its unit is m/s2.
Acceleration = Change in velocity/Time

A decrease in the velocity with time is called deacceleration or retardation. It is otherwise known as negative acceleration.

If the acceleration remains constant, i.e., it does not change with time it is said to be uniform acceleration.

Projectile is the name given to a body which after having been given an initial velocity is allowed to move under the influence of gravity alone.

The path of the projectile is called trajectory

The trajectory of a projectile moving under the influence of a constant acceleration is a parabola.

A projectile has maximum range when the angle of projection is 45°.

Types of Motion

Translatory motion is a motion in which every part of a body moves in the same direction by an equal distance at the same time. eg: Moving vehicles like cars, buses, trains.

Rectilinear motion is a motion along a straight line.
eg: The up and down movement of lifts.

Curvilinear motion is a motion along a curved path.
eg: The motion of a rocket in space.

Rotatory or Circular motion is a motion in which different parts of a body move around a central fixed point or axis in a circular path with different radii.
eg: The motion of a spinning wheel.

Oscillatory motion is a motion in which a body moves back and forth about its mean position.
eg: The movement of a swing

Periodic motion is a motion which repeats itself after a fixed interval of time.
eg: The rotation of the earth around the sun.

All oscillatory motions are periodic motions.

If the motion of an object is restricted to a straight line, it is an one dimensional motion.
eg: Train running along a straight track.

If the motion of an object is restricted to a plane, it is a two dimensional motion.
eg. motion of a boat on a lake, a coin along a surface, motion of projectiles, satellites, motion of charged particles in electric and magnetic fields.

An object moving in space is said to be in three dimensional motion.
eg: A butterfly flying in air or motion of gas molecules in space.

Momentum (P) is defined as the product of mass and velocity of a body. i.e, P = mv. Momentum is a vector quantity.Unit of momentum is kg m/s.

Inertia is the tendency of a body to continue in its state of rest or the state of uniform motion along a straight line. Galileo discovered law of inertia. An athlete run a few distance prior to taking a long jump, by running the athlete provides himself larger inertia of motion.

As the train starts moving through the railway track, a man sitting inside the train leans backwards due to inertia of rest.

When a shot is fired from a gun, the gun recoils due to the reaction force applied by the shot on the gun.

In order to gain stability, an individual climbing a hill bends forward.

The flying of birds is a consequence of Newton’s Third law of motion.

Action and reaction are equal and opposite but they never cancel each other as they act on different objects.

Swimming is possible on account of third law of motion.

Rocket works according to Newton’s third law and law of conservation of linear momentum.