Module 3 Key Words

Acceleration

The rate of change of velocity

Average Speed

Distance over time for the entire region of interest

Braking Distance

The distance travelled between the brakes being applied and the vehicle coming to a stop

Displacement

The direct distance between an object’s starting and ending positions (vector quantity)

Displacement-Time Graphs

Plots showing how displacement changes over a period of time

Free-Fall

An object is said to be in free fall when the only force acting on it is the force of gravity

Instantaneous Speed

The exact speed of an object at a specific given point

Projectile Motion

The motion of an object that is fired from a point and then upon which only gravity acts

Reaction Time

The time taken to process a stimulus and trigger a response to it

Stopping Distance

The sum of thinking distance and braking distance for a driven vehicle

Thinking Distance

The distance travelled in the time it takes for the driver to react

Velocity-Time Graphs

Plots showing how velocity changes over a period of time

Velocity

The rate of change of displacement (vector)

Archimedes’ Principle

The upwards force acting on an object submerged in a fluid, is equal to the weight of the fluid it displaces

Centre of Gravity

The single point through which the object’s weight can be said to act

Centre of Mass

The single point through which all the mass of an object can be said to act

Couple

Two equal and opposite parallel forces that act on an object through different lines of action

Density

The mass per unit volume of a material

Drag

The frictional force that an object experiences when moving through a fluid

Equilibrium

For an object to be equilibrium, both the resultant force and resultant moment must be equal to zero

Free-Body Diagram

A diagram showing all the forces acting on an object

Friction

The resistive force produced when there is relative movement between two surfaces

Moment of Force

The product of a force and the perpendicular distance from the line of action of the force to the pivot

Newton

The unit of force

Newton’s Second Law

The sum of the forces acting on an object is equal to the rate of change of momentum of the object

Normal Contact Force

The reaction force between an object and surface

Pressure

The force that a surface experiences per unit area. Measured in Pascals (Pa)

Principle of Moments

For an object to be in equilibrium, the sum of the clockwise moments acting about a point must be equal to the sum of the anticlockwise moments acting about the points

Tension

The resultant of two forces acting on an object in opposite, outwards directions

Terminal Velocity

The maximum velocity of an object that occurs when the resistive and driving forces acting on the object are equal to each other

Triangle of Forces

A method of determining the resultant force of two forces. The two forces are joined tip to tail and the resultant force is given by the force that would complete the triangle

Upthrust

The upwards force that a fluid applies on an object

Weight

The product of an object’s mass and the gravitational field strength at its location

Conservation of Energy

In a closed system with no external forces the total energy of the system before an event is equal to the total energy of the system after the event

Efficiency

The useful output of a system divided by the total output

Gravitational Potential Energy

The energy gained by an object when it is raised by a height in a gravitational field

Kinetic Energy

The energy of an object has due to its motion

Power

The work done or energy transferred by a system divided by the time taken for that to be done

Work Done

The energy transferred when a force moves an object over a distance

Brittle

A brittle object is one that shows very little strain before reaching its breaking stress

Compression

The result of two coplanar forces acting into an object

Compressive Deformation

The changing of an object’s shape due to compressive forces

Ductile

A material is ductile if it can undergo very large extensions without failure

Elastic Deformation

If a material deforms with elastic behaviour, it will return to its original shape when the deforming forces are removed. The object will not be permanently deformed

Elastic Potential Energy

The energy stored in an object when it is stretched

Extension

The increase of an object’s length

Force-Extension Graph

A plot showing how an object extends as the force applied increases

Hooke’s Law

The extension of an elastic object will be directly proportional to the force applied to it up to the object’s limit of proportionality

Plastic Deformation

If a material deforms with plastic behaviour, it will not return to its original shape when the deforming forces are removed. The object will be permanently deformed

Spring Constant

The constant of proportionality for the extension of a spring under a force

Strain

The ratio of an object’s extension to its original length

Stress

The amount of force acting per unit area. It’s unit is the Pascal (Pa)

Tensile Deformation

The changing of an object’s shape due to tensile forces

Ultimate Tensile Strength

The maximum stress that an object can withstand before fracture occurs

Young Modulus

The ratio of stress to strain for a given material. Its unit is the Pascal (Pa)

Conservation of Momentum

The total momentum of a system before an event must be equal to the total momentum of the system after the event, assuming no external forces act

Elastic Collisions

A collision in which the total kinetic energy of the system before the collision is equal to the total kinetic energy of the system after the collision

Impulse

The change of momentum of an object when a force acts on it. It is equal to the product of the force acting on the object and the length of time over which it actsI

Inelastic Collisions

A collision in which the total kinetic energy of the system before the collision is not equal to the kinetic energy of the system after the collision

Linear Momentum

The product of an object’s mass and linear velocity

Newton’s First Law

An object will remain in its current state of motion, unless acted on by a resultant force. An object requires a resultant force to be able to accelerate

Newton’s Second Law

The sum of the forces acting on an object is equal to the rate of change of momentum of the object

Newton’s Third Law

Every action has an equal and opposite reaction.