Definitions 3

• Acceleration is the rate of change of velocity
• Average speed is the distance over time for the entire region of interest
• Braking distance is the distance travelled between the brakes being applied and the vehicle coming to a stop
• Displacement is the direct distance between an object’s starting and ending positions, it is a vector quantity
• Displacement-Time Graphs show how displacement changes over a period of time, the gradient gives the velocity, and curved lines represent acceleration
• Free-Fall occurs when the only force acting on an object is gravity
• Instantaneous speed is the exact speed of an object at a specific given point
• Projectile Motion is the motion of an object fired from a point and only gravity acts on it, it can be split into horizontal and vertical components for problem-solving
• Reaction time is the time taken to process a stimulus and trigger a response, affected by alcohol, drugs, and tiredness
• Stopping distance is the sum of thinking distance and braking distance for a driven vehicle
• Thinking distance is the distance travelled after a problem before the driver brakes, affected by alcohol, drugs, and tiredness
• Velocity-Time Graphs show how velocity changes over a period of time, the gradient gives acceleration, and curved lines represent changing acceleration
• Velocity is the rate of change of displacement, a vector quantity
• Archimedes’ Principle states that the upwards force on an object submerged in a fluid is equal to the weight of the fluid it displaces
• Centre of Gravity is the single point through which the object’s weight acts
• Centre of Mass is the single point through which all the mass of an object acts
• Couple consists of two equal and opposite parallel forces that cause rotation without translation
• Density is the mass per unit volume of a material
• Drag is the frictional force experienced by an object moving through a fluid
• Equilibrium requires the resultant force and resultant moment acting on an object to be zero
• Free-Body Diagram shows all forces acting on an object, useful for mechanics problems
• Friction is the resistive force between surfaces with relative movement
• Moment of Force is the product of a force and the perpendicular distance to the pivot
• Newton is the unit of force
• Newton’s Second Law states that the sum of forces on an object equals the rate of change of momentum, expressed as the net force equaling mass times acceleration
• Normal Contact Force is the reaction force between an object and a surface
• Pressure is the force per unit area, measured in Pascals (Pa)
• Principle of Moments states that for equilibrium, the sum of clockwise moments equals the sum of anticlockwise moments
• Tension results from two forces acting on an object in opposite, outwards directions
• Terminal Velocity is the maximum velocity when resistive and driving forces are equal
• Triangle of Forces determines the resultant force of two forces by completing a triangle
• Upthrust is the upwards force a fluid applies on an object
• Weight is the product of an object’s mass and gravitational field strength
• Conservation of Energy states that in a closed system with no external forces, total energy before an event equals total energy after, even if in different forms
• Efficiency is the useful output of a system divided by the total output
• Gravitational Potential Energy is gained by an object when raised in a gravitational field
• Kinetic Energy is the energy due to an object's motion, transferred when it decelerates to rest
• Power is work done or energy transferred divided by the time taken
• Work Done is the energy transferred when a force moves an object over a distance
• Brittle objects show little strain before breaking stress