# Physics Notes – Important Definitions – Static Science GK Material for Competitive exams

### Important Definitions and Laws of Physics

- SCALAR QUANTITIES – Physical quantities which have magnitude only and no direction are called scalar quantities. E.g. : Mass, speed, volume, work.
- VECTOR QUANTITIES – Physical quantities which have magnitude and direction both and obey triangle law are called vector quantities. E.g. : Displacement, velocity, acceleration.
- DISTANCE – Distance is the length of actual path covered by a moving object in a given time interval.
- DISPLACEMENT – Shortest distance covered by a body in a definite direction is called displacement.
- Distance is a scalar quantity whereas displacement is vector quantity but both both having same unit(metre).
- SPEED – Distance traveled by the moving object in unit time interval is called speed i.e. Speed = Distance/Time.
- Speed is a scalar quantity and its SI unit is metre/second (m/s).
- VELOCITY – Velocity of a moving object is defined as the displacement of the object in unit time interval i.e. Velocity = Displacement/Time.
- Velocity is a scalar quantity and its SI unit is metre/second.
- ACCELERATION – Acceleration of an object id defined as the rate of change of velocity of the object i.e. Acceleration = Change in Velocity/Time.
- Acceleration is a vector quantity and its SI unit is metre per second square.
- ANGULAR VELOCITY – The angle suspended by the line joining the object from the origin of circle in unit time interval is called angular velocity.
- NEWTON’S FIRST LAW OF MOTION – Every body maintains its initial state of rest or motion with uniform speed on a straight line unless an external force acts on it.

First law is also called law of Galileo or law of inertia. - NEWTON’S SECOND LAW OF MOTION – The rate of change in momentum of a body is directly proportional to the applied force on the body and takes place in the direction of force . If F = force applied, a = acceleration produced, and m = mass of body then F = ma.
- NEWTON’S THIRD LAW OF MOTION – To every action, there is equal and opposite reaction. E.g. : Recoil of a gun.
- PRINCIPLE OF CONSERVATION OF LINEAR MOMENTUM – If no external force acts on a system of bodies, the total linear momentum of the system of bodies remains constant.
- IMPULSE – When a large force acts on a body for very small time, then the force is called impulsive force. Impulsive is defined as the product of force and time. Impulsive = force*time = change in momentum.
- CENTRIPETAL FORCE – When a body travels along a circular path, its velocity changes continuously. Naturally an external force always acts on the body towards the centre of the path.
- CENTRIFUGAL FORCE – In applying the Newton’s laws of motion, we have to consider some forces which cannot be assigned to any object in the surrounding. These forces are called pseudo force or inertial force.

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