P8 forces in balance

• a scalar is a physical quantity which can only be measured with size/magnitude
• a vector is measured using both magnitude and direction
• distance, volume, speed, mass and temperature are all scalar quantities
• displacement, acceleration, velocity, force and energy are all vector quantities
• friction, air resistance, tension and reaction are all contact forces
• gravitation forces, electrostatic forces and magnetic forces are all non contact forces
• a machine is something that makes a job easier to do
• gears are used for transmitting power from one part of a machine to another
• when you pass power from one gear to another you can increase speed, force and change direction
• force magnifier


  using a small force to make a larger force
• if the effort is applied to the lever further from the fulcrum than the load it's a force multiplier
• the load is what a lever moves
• if forces are balanced, the resultant force is 0N
• moment 


  the moment of a force is the turning effect of the force
• if the anticlockwise and clockwise moment are equal, then the object is balanced
• centre of mass


  the point through which all the mass appears concentrated
• for a symmetrical object the centre of mass lies along the axis of symmetry
• if a suspended, then released, it will come to rest with it's centre of mass directly below the point of suspension
• to stop an object toppling over

  • the centre of mass should be as low as possible
  • the base should be wide (so the line of action of the weight remains inside the base)
  • the base could be bolted down
• an object will topple over if

  • there is a resultant moment on the object
  • the sum of the clockwise moment isn't equal to the anticlockwise moment
• resultant force


  a single force that can replace all of the other forces acting on something

  forces can be added together to give the same effect as the separate forces
• we can use parollelograms to calculate resultant force