forces

• SCALAR QUANTITIES: something you measure -magnitude (size)

  eg. speed/mass

  VECTOR QUAUNTITIES: both direction and magnitude
• RESULTANT FORCE: The force that is produced by the reaction of the two objects.

  -we have 2 opposing forces

  -5-2

  -resultant force is 2N to the right

  
• CONTACT FORCES: force exerted between 2 objects when touching

  eg. friction, 2 objects in opposing movement against each other creating heat.


  NON-CONTACT FORCES: force exerted between 2 objects that aren't physically touching.

  eg. magnetic force, produced by any magnetic material that's in a magnetic field

  
• GRAVITATIONAL FIELD: all objects with mass have it.

  • The greater the mass = the greater the gravitational field
  • N/kg
  • Earth->9.8N/kg
  • weaker gravitational field = smaller weight of an object
  • Moon->1.6N/kg
  • astronaut weighs less on the moon than they do Earth .
• WEIGHT, MASS & GRAVITATIONAL FIELD STRENGTH:

  mass= a measure of the amount of matter in an object

  weight= a measure of size and pull of gravity on the object

  gravitational field strength= a measure of the amount of gravity


  weight = mass x gravitational field strength

  w=mg

  weight- newtons (N)

  mass- kilograms (kg)

  gravitational field strength- (N/kg)
• WORK DONE:

  • force x distance
  • W=Fd
  • work done W (J)
  • force F (N)
  • distance D (M)

  -when a force of 1N causes a movement of 1M then 1J of work is done

  
• FREE BODY DIAGRAMS:

  • simple drawing to show all the forces acting on an object


  -the object isn't moving up or down, upthrust & weight cancel out

  -thrust is 600N to the right

  
• RESOLVING FORCES:

  • a single force can be broken down into 2 component forces
  • component forces are at right angles to each other
  • they're added together to form a resultant force


  -uses Pythagoras theorem to calculate the child's pulling force

  
• CHANGE OF SHAPE:

  • a change in shape is called deformation
  • elastic deformation is reverse when the force is removed
  • inelastic deformation isn't fully reversed & there's permanent

  change in shape
• HOOKE'S LAW: the extension of an elastic object like a spring

  • extension - when an object increases in length
  • compression - when an object decreases in length


  force = spring constant x extension

  F=ke

  force(F) in (N)

  spring constant(k) in (N/m)

  extension(e) in (m)

  
• ELASTIC POTENTIAL ENERGY:

  • 0.5 x spring constant x (extension)^2
  • Ee= 1/2 ke^2
  • elastic potential energy, Ee (J)
  • spring constant, k (N/m)
  • extension, e (m)

  
• DISTANCE: how far an object moves.

  • no direction
  • scalar quantity


  SPEED: the rate of change of distance

  -no associated direction

  -scalar quantity
• • speed (m/s)
  • time (s)
  • distance (m)

  
• • V=final velocity (m/s)
  • U= initial velocity (m/s)
  • A= acceleration (m/s)2
  • T= time taken (s)

  
• gradient= change in y / change in x
• • the displacement of an object can be calculated from the area under a velocity-time graph
• v2 - u2 = 2 a s

  v= final velocity (m/s)

  u= initial velocity (m/s)

  a= acceleration (m/s)2

  s= displacement (m)
• THREE STAGES OF FALLING:

  1. at the start, the object accelerates downwards due to gravity
  2. as the object's speed increases so does air resistance (friction)
  3. at terminal(end) velocity the object's weight is balanced with the frictional forces so the resultant force is 0
• Newton's 1st Law

  • an object stays in the same state of motion unless a resultant force acts on it


  inertia= the tendency of an object to continue in it's current state
• Newton's 2nd law

  • resultant force = mass x acceleration
  • mass-kg


  inertial mass= how difficult it is to change the velocity of an object
• Newton's 3rd law:

  • every action has an equal & opposite reaction


  Eg.

  • a car on the road
  • the tyre pushes the road back
  • the road pushes the tyre forward
• • stopping distance = thinking distance + braking distance
• thinking distance:

  • tiredness
  • drugs
  • alcohol
  • distractions


  braking distance:

  • road conditions
  • weather
  • vehicle conditions
• MOMENTUM = MASS x VELOCITY

  mass=kg

  velocity=m/s

  momentum=(kg m/s)

  Eg.

  an elephant has no momentum when stationary

  when it walks it gains momentum

  faster walker= larger momentum

  
  

  -vector quantity

  -has direction & magnitude
• total momentum before the event = total momentum after the event


  canon being fired:

  -ball moves forward

  -cannon moves backwards

  opposite directions