**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 + ½at

^{2}
2as = v

^{2}– u^{2}
where

v — final velocity

u — initial velocity

t — time interval

a — acceleration

s — displacement

**Facts about Motion**

■ 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/s

^{2}.
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.

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