Hey readers, today we will go through the terms related with the key topic “Motion”, the core of forces.

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**Scalar Quantities – **Physical quantities which have magnitude only and have no direction are called scalar quantities. Eg: Mass, speed, volume, work, time, power, energy etc.

**Vector Quantities – **These have magnitude and direction both, which obey triangle law. Eg: Displacement, velocity, force, momentum, torque etc.

- Moment of inertia, pressure, refractive index, stress are called tensor quantities.
- Electric Current has a direction but it is a scalar quantity because it does not obey the law of triangle.

**Distance **– It is the length of actual path covered by moving object in a given time interval. It is a scalar quantity.

**Displacement** – It is a shortest distance covered by a body in a definite direction. It is a vector quantity. Displacement may be positive, negative or zero, whereas distance is always positive.

**Velocity** – The rate of change of distance is called velocity. It is a vector quantity and is SI unit is metre/second. It may be positive or negative.

**Formula**– Displacement/Time

**Acceleration** – It is the rate of change of velocity. It is a vector quantity.

**SI Unit**–**m/s**^{2}**Formula**– Change in Velocity/Time**Relation with acceleration**– When the velocity of body increases, then its acceleration is positive and vice versa.- If the velocity of body decreases, then its acceleration is called retardation.

**Centripetal Force** – A body performing circular motion, its body changes continuously. The external force required to maintain the circular motion of the body is called centripetal force.

- This force is always directed towards the centre.
**Formula**–**MV**where m=mass, s=uniform speed and r=radius^{2}/R

**Centrifugal Force** – In applying the Newton’s laws of motion, there are some forces which cannot be assigned to any object in the surrounding.

- These forces are called pseudo forces or inertial force.
- Centrifugal force is a pseudo force. It is equal and opposite to centripetal force. Example – Cream separator, centrifugal drier.

**Newton’s law of motion**

**First Law**

His first law states that every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force. This law is also known as law of inertia or law of Galileo.

**Intertia**– It is a property of body by virtue of which the body opposes change in its initial state of rest or motion with uniform speed on a straight line.- It is of three types –
**Inertia of rest**,**Inertia of motion**and**Inertia of Direction**.

**Second Law**

The rate of change in momentum is directly proportional to the applied force on the body and takes place in the direction of force.

**Force**– External energy on a body which changes or tries to change the initial state of the body.**Momentum**– It is strength or force that something has when it is moving. It is the product of the mass and velocity of the body. It is a vector quantity. Its SI unit is**Kgm/s**.

**Third Law**

For every action there is an equal and opposite reaction. Example – While sitting on chair your body exerts a force downward and that chair needs to exert an equal force upward or the chair will collapse.

**Impulse**

If the force acts on a body for a very small time, it is known as impulive force.

- It is a vector quantity.
- Impulse = Force*Time = Momentum
**SI Unit**– Newton second (Ns)

**Equilibrium**

If resultant of all the forces acting on a body is zero then the body is said to be in equilibrium.

- If the body is in equilibrium, it will be either at rest or uniform motion.
- At rest the equilibrium is called static otherwise dynamic.
- Static equilibrium is of two types – stable and unstable

With this we have completed Today’s topic. Hope you have learned today.

We will post **Quiz on Motion in Today’s Cracking Session**.

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Happy Learning !

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