Module 3 definitions

• 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. It is affected by the vehicle and road conditions
• Displacement


  The direct distance between an object's starting and ending positions. It is a vector quantity and so has both a direction and a magnitude
• Displacement-Time Graphs


  1. Plots showing how displacement changes over a period of time

  2. The gradient gives the velocity

  3. Curved lines represent an acceleration
• 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
  • When solving projectile motion problems, it is useful to split the motion into horizontal and vertical components
• Reaction Time


  • The time taken to process a stimulus and trigger a response to it
  • It is affected by alcohol, drugs and tiredness
• 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
  • It is affected by alcohol, drugs and tiredness
• Velocity-Time Graphs


  1. Plots showing how velocity changes over a period of time

  2. The gradient gives acceleration

  3. Curved lines represent changing acceleration
• Velocity


  • The rate of change of displacement
  • It is a vector quantity and so has both a direction and a magnitude
• 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
  • It has the effect of causing a rotation without translation
• 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 acting on the object must be equal to zero
• Free-Body Diagram


  • A diagram showing all the forces acting on an object
  • It is a good starting point to any mechanics problem
• 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
  • It is also expressed as the net force acting an object equaling the product of the object's mass and acceleration
• Normal Contact Force


  The reaction force between an object and surface
• Pressure


  • The force that a surface experiences per unit area
  • It is 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 point
• Tension


  The result 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
  • The energy does not need to be in the same form after the event as it was before the event
• Efficiency


  The useful output (e.g. power, energy) 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 an object has due to its motion
  • It is the amount of energy that would be transferred from the object when it decelerates to rest
• 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