Physics defs Topic 2: Motion and Forces

Acceleration due to Gravity:

Gravity acting on an object in freefall causing acceleration. Its value at the surface of Earth is 10 m/s2.

Acceleration:

The rate of change of velocity. It can be calculated from the gradient of a velocity-time graph.

Braking Distance:

The distance a vehicle travels under the braking force. This can be affected by adverse road and weather conditions as well as the condition of the vehicle.

Centripetal Force:

The resultant force that acts towards the centre of the circular path of an object travelling with circular motion.

Circular Motion:

The motion of an object travelling in a circle. An object travelling in circular motion is always accelerating due its continual direction change. This means that a centripetal force is always required.

Conservation of Momentum:

The total momentum of a system before an event is always equal to the total momentum of the system after the event.

Displacement:

A measure of how far an object moves in a given direction. It is the straight line between the starting and finishing points and is a vector quantity.

Distance-Time Graph:

A plot of how an object's distance changes over time. The gradient of the graph at any point, equals the object's speed at that point.

Distance:

A measure of how far an object moves. It doesn't depend on direction and is therefore a scalar quantity.

Free-Fall:

Motion under the force of gravity alone.

Human Reaction Time/Thinking Distance

The time it takes for the brain to react to a stimulus. Typical human reaction times are in the range of 0.2-0.9 seconds.

Inertial Mass:

A measure of how hard it is to change an object's velocity. Inertial Mass= force/acceleration

Momentum:

p= m x v momentum = (mass x velocity)

Newton:

The unit of force.

Newton's First Law:

An object at rest stays at rest (resultant force is zero, the object will remain stationary/will not move). If a moving object's resultant force is zero, the object will continue to move at a constant velocity (same speed and direction).

Newton's Second Law:

An object's acceleration is directly proportional to the resultant force acting on it, and inversely proportional to the object's mass.

Newton's Third Law:

The forces that two objects exert on each other when they interact are equal and opposite.

Resultant Force:

Sum of all forces on an object. Vector quantity as it has direction and magnitude

Scalar Quantities:

Quantities that only have a magnitude, not a direction.

Speed:

A scalar quantity that is a measure of the rate of change of distance. S= d/t

Thinking Distance:

The distance a vehicle travels during the driver's reaction time. This reaction time may be affected by tiredness, drugs or alcohol.

Vector Quantities:

Quantities that have both a magnitude and direction.

They are represented by an arrow, with the length representing the magnitude and the arrowhead representing the direction.

Velocity-Time Graph:

A plot of how an object's velocity changes over time. The gradient = acceleration (at that point). Area under the graph = the object's displacement.

Velocity:

A vector quantity that is the rate of change of displacement. It is the speed in a given direction.

Weight:

The force acting on an object due to gravity. Weight = m x g = mg (mass (kg) x gravity)

It can be measured using a Newton Meter.

Stopping Distance:

stopping distance = thinking + braking distance