AS Key Words

• Quantity


  Represented by a number and a unit
• Scalar


  A quantity that has magnitude only
• Vector


  A quantity that has both magnitude and direction
• Density

  Mass / Volume
• Moment


  The force about a point = the force x the perpendicular distance from the point to the line of action of the force
• The principle of moments


  For a system to be in equilibrium, all anticlockwise moments must equal all clockwise moments about the same point
• Centre of gravity


  The single point at which the entire weight of an object is considered to act
• Displacement


  When the distance between point A to point B is the shortest distance between the two points
• Mean speed


  Total distance travelled / total time taken
• Instantaneous speed


  Rate of change of distance
• Mean velocity


  Total displacement / total time taken
• Instantaneous velocity


  The rate of change of displacement of a body
• Mean acceleration


  Change in velocity / time taken
• Instantaneous acceleration


  Rate of change of velocity of an object
• Terminal velocity


  Constant, maximum velocity of an object when the restive forces on it are equal and opposite to the accelerating force
• Force


  A push or a pull acting upon a body from an external body
• Newton's 3rd Law

  If body A exerts a force on body B, the body B exerts an equal and opposite force on body A
• Resultant force


  The mass of a body x it's acceleration
• Momentum


  An object's mass x the object's velocity
• Newton's 2nd Law


  The rate of change of momentum is proportional to the resultant force acting on it, and takes place in the direction of that force
• The principle of conservation of momenta


  The vector sum of all the momenta of bodies in a system stays constant even if forces act between the bodies, provided there is no external forces
• Elastic collision


  A collision in which there is no change in total kinetic energy
• Inelastic collision


  A collision in which kinetic energy is lost
• Work done


  The product of the magnitude of the force and the distance in the direction of the force
• Principle of conservation of energy


  Energy cannot be created nor destroyed, only transferred from one form to another
• Potential energy


  Possessed by an object by virtue of it's position
• Kinetic energy


  Energy possessed by an object by virtue of its motion
• Elastic potential energy


  Energy possessed by an object when it has been deformed due to forces acting on it
• Energy


  The amount of work a system can do
• Power


  The work done per second
• Hooke's Law


  The tension in a spring or wire is proportional to its extension from its natural length, provided the extension is not too great
• Spring constant


  The force per unit of extension
• Stress


  The force per unit cross-sectional area when equal opposing forces act on a body
• Strain


  The extension per unit length due to an applied stress
• Young modulus


  Tensile stress / tensile strain
• Crystal


  A solid in which the atoms are arranged in a regular long-range order
• Crystalline solid


  Solid consisting of a crystal usually arranged randomly
• Polymeric solid


  A solid which is made up of chain-like molecules
• Ductile material


  A material which can be drawn out into a wire. This implies that plastic strain occurs under enough stress
• Elastic strain


  This is strain that disappears only slightly when the stress is removed, that is the specimen returns to its original size and shape