OCR Physics A level - Module 3 Definitions

Scalar

A scalar quantity has only magnitude (size).

Vector

A vector quantity has both magnitude (size) and direction.

Centre of gravity

The point on a body through which the weight appears to act

Couple

Two forces that are equal in magnitude but opposite in direction and act to produce rotation.

Elastic Deformation

When the load is removed, the material will return to its original shape and size

Plastic Deformation

The deformation of a material beyond its elastic limit (it will no longer return to its original shape and size once the load is removed)

Displacement

The distance moved by an object in a particular direction.

Instantaneous speed

The speed of an object measured at a particular point in time.

Average Speed

The average rate of moving through a distance.

Velocity

The rate of change of the displacement of an object.

Acceleration

The rate of change of an object's velocity.

Torque of a couple

The product of one of the forces of a couple and the perpendicular distance between them.

Moment of a force

The magnitude of the force multiplied by the perpendicular distance between the pivot and the line of action of the force.

Thinking Distance

The distance travelled in a time equal to the reaction time of the driver.

Braking Distance

The distance travelled by a vehicle from the time the brakes are applied until the vehicle comes to a full stop.

Stopping Distance

The sum of the braking distance and the thinking distance (must define these terms).

Work Done by a Force

The product of the force and the distance moved by the force in the direction of travel.

Power

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

Stress

The force acting per unit cross-sectional area.

Strain

The extension per unit length produced by a tensile or compressive force.

Young Modulus

The ratio of stress to strain for a given material, providing Hooke's law is obeyed.

Ultimate Tensile Strength

The breaking stress of a material.

Newton

The force that will give a 1kg mass an acceleration of 1ms-2.

Joule

The amount of work done when a force of 1N is moved through 1m.

Watt

The rate of work done when 1 joule is transferred every second.

Newton's 1st law

An object remains at rest or moving with constant velocity unless a resultant force acts.

Newton's 2nd law

The force acting on an object is proportional to the rate of change of its momentum and acts in the same direction as this change.

Newton's 3rd law

If body A exerts a force on object B (FAB) then object B exerts an equal but oppositely directed force on body A (FBA).

Momentum

(p) is the product of an object's mass (m) and velocity (v) p=mv.

Impluse

the product of average force (F) and the time (Δt) for which it acts. Impulse is equal to the change in momentum (Δp) Δp = F Δt.

Net force

is equal to the rate of change of its momentum.

Conservation of momentum

The total momentum before a collision is equal to the total momentum after a collision provided no external force acts.

Elastic collision

Kinetic energy is conserved. Momentum is always conserved.

Inelastic collision

Kinetic energy is not conserved, some loss of kinetic energy. The bodies are permanently deformed. Momentum is always conserved.