IB Physics Topic a - Space, Time and Motion Key Definitions

Acceleration is the rate of change of velocity.

Air drag is a resistive force that acts on objects moving through air.

Angular acceleration is the rate of change of angular velocity.

Angular displacement is the angle through which an object moves on a circular path. It is measured in radians.

Angular impulse is a concept in rotational motion that describes the change in angular momentum of a rigid body due to the application of torque over a period of time.

Angular momentum is the rotational equivalent of linear momentum. More precisely, it is the product of its moment of inertia and its angular velocity.

Angular velocity ($\omega$) is the rate of change of angular displacement. It is measured in radians per second (rad/s).

Average speed is the total distance traveled divided by the total time taken. It’s a scalar quantity.

Average velocity is the total displacement divided by the total time taken. It’s a vector quantity.

Centripetal force is a force that acts on a body moving in a circular path and is directed towards the centre around which the body is moving.

Collisions are interactions where two or more objects exert forces on each other for a short time.

Angular momentum is conserved unless an external torque acts on the system.

In an isolated system, the total mechanical energy is conserved:

$$E_{\text{total}} = E_k + E_p = \text{constant}$$

Contact forces are forces that arise due to direct physical interaction between two objects.

Drag force is a resistive force that acts opposite to the direction of an object’s motion through a fluid (such as air or water).

Efficiency quantifies how effectively a system converts input energy into useful output energy.

In an elastic collision, both momentum and kinetic energy are conserved.

Elastic potential energy is the energy stored in an elastic object, such as a spring, when it is compressed or stretched.

Energy density is defined as the amount of energy stored per unit volume or mass of a substance.

Friction is a force that opposes the motion of an object.

Gravitational potential energy is the energy stored due to the position of an object in a gravitational field.

Impulse describes how a force applied over a period of time changes an object's momentum.

The impulse-momentum theorem states that the impulse on an object is equal to the change in its momentum

In an inelastic collision, momentum is conserved, but kinetic energy is not.