Forces

Forces

intro
1. measured in newtons (N)
2. makes an object move (e.g. tension)
3. makes an object stop moving (e.g. friction)
4. forces can change the direction of a moving object
5. forces can change the shape of an object
contact forces
1. impact force
  1. when 2 objects bump into each other
  2. when a particle in the air hits your skin
  3. when a tennis ball hits a racket
2. strain force (tension)
  1. when an object is stretched
  2. when an elastic band or string is stretched
  3. when a ball hits the strings on a tennis racket
3. friction
friction
1. slows down a moving object
  1. e.g. goalkeeper gloves
2. surfaces
  1. smooth surfaces
    1. reduce friction
  2. rough surfaces
    1. increase friction
3. uses
  1. good uses of friction
    1. between foot and ground
    2. studs on trainers
    3. football gloves
    4. brake pads
  2. bad uses of friction
    1. generates heat
      1. rubbing hands together
      2. moving parts in car rub together
    2. causes particles to heat up
      1. causes dust particles in comets
      2. can be a problem when space shuttles are sent into space because they get very hot
non contact forces
1. magnetic force
  1. exerts a pulling force on some materials without pulling it
  2. closer the magnet is, stronger the force is
  3. 2 magnets can also exert a pushing force on each other
2. electrostatic force
  1. created when 2 forces are rubbed together
  2. rub a comb on a jumper
  3. 2 charged objects exert a force on each other without touching each other
  4. e.g. if you hold a charged comb near water running from a tap, you can bend the flow of the water
3. gravitational force
  1. force of attraction between any 2 masses in universe
  2. e.g. the force between body and ground
  3. gravitational force between planets
  4. on earth, all masses are attracted to the earth itself
  5. size of force depends on mass
    1. greater mass
      1. stronger force
    2. lower mass
      1. weaker force
  6. gravitational force acting on any mass is called weight and is measured in newtons (N)
  7. weight on earth = mass x 9.82N/kg
speeding up, slowing down
1. when force is applied to stationary object it may begin to move
  1. e.g. footballer kicks the ball
2. when a force is applied to a moving object in the opposite direction of motion, it will slow down or even stop
  1. e.g. football may be stopped quickly by the impact force of the goalkeeper
  2. e.g. football may be stopped slowly by the contact force of friction as it rolls on the ground
3. when a force is applied to a moving object in the same direction of motion, it will speed up
upthrust
1. when an object is in aliquid it experiences an upwards force called upthrust
2. caused by water being pushed out of the way
3. determined by volume of the object and density of the liquid
4. upthrust makes things weigh less when in a liquid
5. if upthrust is large enough to balance the wight of the object, it will float
balanced forces
1. a skydiver experiences 2 forces
2. gravitational force and friction with the air (drag) upwards
3. if 2 forces are equal size the skydiver neither slows down or speeds up
4. the forces are said to be balanced
density
1. measure of how heavy something is for its size
2. calculated with this equation: density = mass/volume

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