forces

• Vector quantity


  Quantity with size and direction
• Scalar quantity


  Quantity with size only
• Vector quantities


  • force
  • acceleration
  • velocity
  • weight (it's a force)
  • momentum
  • displacement
• Scalar quantities


  • temperature
  • speed
  • distance
  • mass
  • energy
  • power
  • work
• Force


  A push or a pull that acts on an object due to an interaction with another object
• Contact forces


  • The objects are physically touching
• Non-contact forces


  • The objects are physically separated
• Force is a vector quantity
• Weight


  The force acting on an object due to gravity
• Mass


  Unit is kilogram (kg)
• Weight


  Unit is newton (N)
• Gravitational field strength


  Unit is newtons per kilogram (N/kg)
• Centre of mass


  The point where the weight appears to act
• Measuring instrument for weight

  Calibrated spring balance or newtonmeter
• Resultant force


  The single force that has the same effect as a number of forces acting together
• A car engine provides a force E to drive the car forward


  A frictional force F acts backwards on the car
• Adding forces


  Add vectors by joining them nose to tail. The resultant is the single vector that replaces them.
• Resolving forces into components

  Draw horizontal and vertical lines from the ends of your vector. These are the components.
• Equilibrium of forces


  Add the vectors by joining them nose to tail. They form a closed shape, showing that they sum to zero.
• Work done


  When a force moves through a distance
• Work done


  Energy transferred
• Newtonmetres and joules


  They are identical. A joule is the name of a newtonmetre.
• Unit of work


  joule
• Force moves through a distance, work is done and energy is transferred


  Kinetic store (if the moving force increases the speed of an object)
• Force moves through a distance, work is done and energy is transferred


  Gravitational store (if the moving force increases the height of an object)
• Force moves through a distance, work is done and energy is transferred


  Thermal store (if the moving force does work against friction)
• To change the shape of an object, more than one force has to be applied
• Inelastic (plastic) deformation


  Deformation where the object does not return to its original shape when the force is removed
• Elastic deformation


  Deformation where the object returns to its original shape when the force is removed
• Limit of proportionality


  The maximum load that will still allow a material to return to its original shape when the load is removed
• Elastic Limit


  The maximum load for which the extension of a spring is proportional to the load applied
• The force-extension graph for a Hookean material is a straight line through the origin
• Hooke's Law


  The extension of a spring is proportional to the load applied
• Spring constant


  Unit is newton per metre (N/m)
• Extension


  Unit is metre (m)
• e in F = k e

  Extension (if the spring is being stretched) or compression (if the spring is being squashed)
• v, u, a, s

  final velocity, initial velocity, acceleration, distance
• Force moves through a distance, work is done and energy is transferred


  Elastic potential energy store (if the moving force stretches a spring)
• If the spring is stretched beyond its elastic limit and is deformed inelastically, the thermal store is filled
• k in Ep = 1/2 k e^2


  Spring constant