keypoints

• Vectors


  Have both a magnitude and a direction, compared to scalar quantities which only have a magnitude
• Vectors


  • Can be shown with arrow drawings
  • If drawn to scale then they can be physically measured
  • If not, maths must be used
• Vector triangles


  1. Determine whether the forces are balanced (and with a resultant force of 0N) or not

  2. This is called resultant vectors
• Resolving a vector


  1. Splitting it up into its horizontal and vertical components

  2. Because horizontal and vertical meet at right angles they can be calculated using trigonometry

  3. They can also be drawn to scale and found using the 'parallelogram method'

  4. The key is putting the vectors head to tail
• Moment of a force

  The product of the force and the distance from its line of action to the point
• Where an object is in equilibrium, the moments on it about a point are balanced
• Couple


  A pair of equal and opposite parallel forces acting on the same body that do not act in the same line
• Total Clockwise Moment = Total Anticlockwise Moment
• Moment of a Couple

  Force (N) x Perpendicular Distance Between Lines of Action (m)
• Centre of mass


  • Where the mass of an object can be considered to be concentrated
  • The line of action acts from the centre of mass and shows how gravity is acting upon the object
• Finding the centre of mass

  Suspend an object by a pin and then use a plum line to draw on the line of action- where they cross is the centre of mass
• If the line of action falls outside of the width of the base then the object will topple
• Newton's first law


  The velocity of an object will not change unless a resultant force acts upon it
• Newton's second law


  f=ma (force in N equals mass in kg times the acceleration in ms-2)
• Newton's third law


  Every force has an equal and opposite force
• SUVAT


  • S= Displacement
  • U= Initial velocity
  • V= Final velocity
  • A= Acceleration
  • T=Time
• In projectile motion, the horizontal and the vertical components are treated separately
• Acceleration is due to gravity, hence only affects the vertical component and is positive if acting with the object and negative if against it
• Friction


  A force that opposes motion when moving on a solid
• Drag


  A force that opposes motion in a fluid. It usually increases with speed
• Lift


  An upward force created on an object as it moves through a fluid due to the shape of an object
• Terminal Velocity


  Happens when frictional forces equal the driving force, causing equilibrium and zero acceleration
• In a closed system, momentum is conserved
• Inelastic collision


  Kinetic energy is not conserved
• Elastic collision


  Kinetic energy is conserved
• Impulse


  The change in momentum or the product of force and time
• Area under a force-time graph is impulse
• Work


  Done when a force is applied across a distance
• Energy


  Measured in joules
• Power


  Measured in watts, where one watt is equal to one joule per second
• Efficiency


  Useful Output Power / Input Power
• Density


  Mass of a material per unit volume
• Finding the density of a liquid


  Measure its mass and volume
• Finding the density of a solid


  Measure its mass and the volume of water it displaces
• Hooke's law


  The force applied is directly proportional to the extension
• Limit of proportionality


  The point beyond which Hooke's law no longer applies
• Elastic limit


  The maximum stress that can be applied without permanent/plastic deformation
• Elastic Deformation


  Material returns to original shape and has no permanent extension. Energy is stored as elastic strain energy
• Plastic Deformation


  Material is permanently stretched because the atoms have physically moved relative to one another. Energy is used to deform it
• Tensile Stress


  The force applied per unit cross-sectional area, measured in Pa or Nm-2