Forces

• weight= force due to gravitational field of earth on an object of mass. Acts towards centre of planet.
• Normal Reaction Force= The normal reaction is the force acting on the body when it is kept on a surface.  Force from a surface on an object on that surface. Acts up from the surface ( at 90* from surface)
• Friction = Resistance between two surfaces that are moving or trying to move past one another. Frictional forces always act opposite to motion, so they oppose relative movement between objects.
• Tension = Pulling force exerted by a string or rope. Tension acts along the length of the string/rope.
• Weight - The force experienced by an object due to gravity. Weight is equal to the product of mass and gravitational field strength.
• Gravitational Field Strength - The strength of the gravitational pull at any point in space. It depends on the mass of the object causing the field and its distance from the object.
• Force


  • An action that can shape an object or change its motion (speed it up, slow it down or change its direction)
• Force is measured in Newtons
• You write capital N for Newtons
• Measuring a force

  Using a NEWTON METER
• Elastic Potential Energy = Stored energy in a stretched or compressed elastic material. Elastic potential energy can be transferred into kinetic energy if the object is released.
• Force


  Something which pushes and pulls
• Common named forces

  • Weight
  • Normal Reaction force
  • Electrostatic force
  • Magnetic force
  • Thrust
  • Drag
  • Friction
  • Lift
  • Tension
  • Compression
  • Upthrust
• Weight

  Force due to gravitational field of Earth on an object of mass, Acts towards centre of planet
• Normal Reaction force

  Force from a surface on an object on that surface. Acts up from the surface at 90 degrees from surface
• Electrostatic force


  Acts between two charged objects. Direction depends on type of charge (like charges repel, opposites attract)
• Magnetic force

  Acts between two magnetic poles. Direction depends on type of pole (like poles repel, opposite poles attract) (North and south)
• Thrust

  Can be force applied due to engine/rocket
• Drag

  Resistance whilst swimming. Force which acts in opposite direction to motion of object in a fluid (gas or liquid). This will slow a moving object down.
• Friction


  Contact force between two surface which acts in opposite direction to motion. This will slow a moving object down.
• Lift

  The force that a wing has which allows it to rise due to the vertical motion of the plane/bird
• Tension


  The force you have in a rope/cable being pulled
• Compression


  A force a squashed object experiences
• Upthrust

  The upward force that a liquid or gas exerts on a body floating in it
• Interpreting a distance-time graph

  1. Identify the part of the graph where the bus travels the slowest

  2. Look for the part of the graph with the least steep line
• The line between points D and E on the distance-time graph is the least steep
• This indicates the bus travels the slowest between points D and E
• Scales


  Device used to check the weights of silver coins
• Scales


  • Pan X
  • Pivot
• Rema puts a silver coin in pan X


  Pan X moves downwards
• Weights of silver coins


  • A: 106 mN
  • B: 112 mN
  • C: 98 mN
  • D: 112 mN
  • E: 120 mN
• Balancing the scales

  Putting one coin in each pan so the scales are balanced
• Coins that balance the scales

  • B and D
• Coin A is placed in pan X, and coin C is placed in pan Y

  Pan X moves downwards
• Force of the ball on the spring


  Direction shown by arrow
• Force of the spring on the ball


  Direction shown by arrow
• Metal balls attached to identical springs

  • Ball A
  • Ball B
  • Ball C
• Heaviest ball

  Ball B
• The spring is more elongated
• More elongated spring


  Indicates greater weight due to gravitational field which pulls on object towards centre of the earth