A-unit physics

Displacement

Distance traveled in a particular direction (change in position)

Velocity

Rate of change of displacement

Speed

Rate of change of distance

Acceleration

Rate of change of velocity

Newton’s First Law of Motion

An object at rest remains at rest and an object in motion remains in motion at a constant speed in a straight line unless acted on by an unbalanced force.

Newton’s Second Law of Motion

An unbalanced force will cause an object to accelerate in the direction of the net force. The acceleration of the object is proportional to the net force and inversely proportional to its mass.

Newton’s Third Law of Motion

When two bodies A and B interact (push or pull), the force that A exerts on B is equal and opposite to the force that B exerts on A.

Translational Equilibrium

Net force acting on a body is zero

(Linear) Momentum, p

Product of mass and velocity. Direction of momentum is in the direction of motion

Impulse, J

Change in momentum

Law of conservation of (linear) momentum

The total momentum of an isolated system (no external forces) remains constant

Angular displacement

The angle moved around the circle by an object from where its circular motion starts

Angular velocity

Angular displacement per unit time, same as angular frequency.

Isolated system

A system that is not affected by an external force. Momentum is conserved.

Work, W

The product of a force on an object and the displacement of the object in the direction of the force.

Kinetic energy, Ek

The energy an object has due to its motion. Product of ½ times the mass of an object times the square of an object's speed

Gravitational potential energy, Ep

Energy an object has due to its position in a gravitational field (due to its vertical position → height).

Principle of conservation of energy

The total energy of an isolated system (no external forces) remains constant. Energy can be neither created nor destroyed but only transformed from one form to another or transferred from one object to another.

Elastic collision

A collision in which kinetic energy is conserved + momentum is conserved

Inelastic collision

A collision in which kinetic energy is not conserved.

Explosion

A single object that splits into two or more objects; momentum is conserved in this case.

Power, P

The rate at which work is done or the rate at which energy is transferred.

Efficiency

The ratio of the useful energy (or power or work) output to the total energy (or power or work) input

Torque

Measure of the force that can cause an object to rotate about an axis

Rotational equilibrium

When the sum of the torques acting on a body is zero, giving it zero net angular acceleration. Clockwise torques = anticlockwise torques

Moment of inertia

A measure of an object's resistance to changes in its rotational motion, ratio of applied torque and angular acceleration, formula depends on the object.

Angular momentum

Rotational equivalent of linear momentum.

Frame of reference

A coordinate system used to describe motion and position of objects, observer's point of view

Inertial reference frame

A frame of reference in which Newton's laws of motion apply, moves at constant velocity in respect to other reference frames

Non-inertial reference frame

A reference frame that is accelerating or rotating; Newton's laws do not apply

Galilean Relativity Principle

The laws of physics are the same in all inertial reference frames

First postulate of special relativity

The laws of physics are the same in all inertial frames of reference, (same as galilean relativity)

Second postulate of special relativity

The speed of light in a vacuum is the same as measured by all inertial observers

Space-time interval

The invariant distance in space-time between two events, same value in all inertial reference frames

Proper time

Time interval measured by an observer in the same reference frame in which the events occur, max. time interval between two events

Proper length

The length measured in the reference frame in which the object is at rest, the max. length of an object

World line

The path of an object through space-time

Muon experiment

When muons are moving near the speed of light (0.98c), their half-life is increased when measured by a stationary observer on Earth. This dilated half-life as observed by an Earth-bound observer allows muons to reach the surface of Earth before decaying. This experiment serves as evidence for time dilation and length contraction.

Space-time diagrams

• Vertical axis represents time (ct)

• Horizontal axis represents space (x)

• Light rays are represented by lines at a 45 degree angle