Physics

• Every measurement or quantity has a unit
• Units

  • Meters for distance
  • Seconds for time
• Prefixes

  • Used for very big or very small numbers
  • Generally go up or down in thousands times 1,000
  • Divide by a th000
• Centimeters and decimeters are exceptions to the prefix rule
• Converting units

  1. Think do I want a bigger number multiplied by the conversion factor or a smaller number

  2. If smaller, divide by the conversion factor
• Prefixes in standard form

  • Bigger than a meter: Positive power on 10
  • Smaller than a meter: Negative power on 10
• Force


  • Any push or pull
  • Can be contact forces (physically touching) or non-contact (like magnetism, electrostatic, gravity)
• Representing forces

  • With vectors (arrows showing direction and magnitude)
  • Magnitude is the size of the force, indicated by length of arrow
• Finding resultant force

  1. Technically add the vectors

  2. If in opposite directions, one must be negative

  3. If at right angles, use Pythagoras or trigonometry
• Balanced forces

  • Forces add up to zero
  • Object will not accelerate, stays at constant velocity (which could be zero)
• Scalar


  Measurement or quantity with magnitude but no direction
• Vector

  Measurement or quantity with both magnitude and direction
• Weight

  • Force due to gravity acting on an object
  • Calculated as mass * gravitational field strength (9.8 N/kg or 10 N/kg)
• To lift an object upwards at constant speed, the upward force must equal its weight
• Work done

  • Energy transferred by a force
  • Calculated as force * distance moved
• Gravitational potential energy

  • Energy gained when an object is lifted
  • Calculated as mass * gravitational field strength * height
• Moment

  • Turning force
  • Calculated as force * perpendicular distance to pivot
• If clockwise and anticlockwise moments are balanced, the object will not turn
• Gears

  Application of moments to increase the moment produced
• Speed and velocity

  • Measured in m/s
  • Velocity has direction (can be positive or negative)
• Calculating speed and velocity

  1. Speed = distance / time

  2. Velocity = displacement / time
• Speed/velocity time graph

  Gradient = acceleration (m/s^2)
• Acceleration due to gravity is 9.8 m/s^2
• Distance from speed/velocity time graph

  Area under the graph
• Newton's equations of motion

  • Used to predict an object's motion when accelerating
  • Involve variables: displacement, initial velocity, final velocity, acceleration, time
• Newton's first law

  If no resultant force, motion is constant (no change in velocity)
• Inertia

  Tendency for an object's motion to stay constant unless acted on by a resultant force
• Newton's second law

  Force = mass * acceleration
• Proving Newton's second law

  1. Use a trolley on a track, pulled by weights over a pulley

  2. Measure acceleration with light gates

  3. Plot force vs acceleration graph, should be straight line through origin
• Newton's third law

  For every action force, there is an equal and opposite reaction force
• Thinking distance

  Distance travelled before reacting to something
• Doubling speed

  Quadruples braking distance
• Momentum

  • Measure of how hard it is to stop something
  • Calculated as mass * velocity
• In a collision, total momentum is always conserved
• Force and momentum

  Force = rate of change of momentum
• Energy


  Cannot be created or destroyed, only converted between different stores
• Energy stores

  • Kinetic energy
  • Gravitational potential energy
  • Elastic potential energy
• Every measurement or quantity has a unit
• Kinetic energy

  Calculated as 1/2 * mass * velocity^2
• Units

  • Meters for distance
  • Seconds for time