- The study of moving objects under the action of force is called dynamics and the study of forces on bodies at rest is called statics.
- The centre of gravity of an object is a fixed point through which the entire weight of the object acts, irrespective of the position of the object.
- The acceleration due to gravity decreases with increasing altitude and it decreases with depth.
- The stability of a body is decided by the position of the centre of gravity. A body will be stable if the vertical line through the centre of gravity falls within the base.
- A projectile is defined as a body which is given an initial velocity and then allowed to move under the action of gravity.
- The Range of a projectile is the horizontal distance between the point of projection and the point where the projectile hits the ground.
- The movement of a particle in a circular path is called circular motion.
- Angular displacement of an object is measured by the angle swept by the radius at the centre as the particle moves along the circumference of a circle
- The unit of angular displacement is radian. One radian is defined as the angle subtended at the centre of the circle by an arc whose length is equal to its radius.
- Angular velocity of an object is the rate of change of angular displacement.
- Angular momentum of a particle is defined as the moment of linear momentum of the particle about the axis of rotation.
- The moment of inertia is defined as the measure of inertia of a rotating particle and is equal to the product of the mass of the particle and the square of its distance from the axis of rotation.
- The external force required to make a body move along a circular path with uniform speed and directed towards its centre is called centripetal force.
- When a body moves along a circular path, the direction of velocity changes at every point and hence it has an acceleration which is directed towards the centre. This acceleration is called centripetal acceleration.

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