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

  • Positive powers for anything bigger than a meter
  • Negative powers for anything smaller than a meter
• Force


  Any push or pull
• Types of forces


  • Contact forces (physically touching)
  • Non-contact forces (like magnetism, electrostatic, gravity)
• Representing forces


  With vectors (arrows showing direction and magnitude)
• Finding resultant force


  1. Technically add the vectors

  2. If in opposite directions, one is negative

  3. Use Pythagoras if at right angles

  4. Use trigonometry (SOHCAHTOA) to find angles
• Balanced forces


  Forces add up to zero, object will not accelerate but may still be moving at constant velocity
• Scalar


  Measurement or quantity with only magnitude, no direction
• Vector


  Measurement or quantity with both magnitude and direction
• Examples of scalars and vectors

  • Scalars: distance, speed, weight
  • Vectors: displacement, velocity, force
• Weight


  Force due to gravity acting on an object, calculated as mass * gravitational field strength
• Gravitational field strength on Earth is 9.8 N/kg, often rounded to 10 N/kg
• 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, a small gear can turn a large gear to increase the moment
• Speed and velocity


  Measured in m/s, velocity has direction
• Calculating speed and velocity


  Distance or displacement over time
• Acceleration


  Rate of change of velocity, measured in m/s^2
• Acceleration due to gravity is 9.8 m/s^2
• Velocity-time graph


  Gradient gives acceleration, area under graph gives displacement
• Newton's equations of motion

  Equations to predict an object's motion when accelerating
• Newton's first law: an object's motion is constant if there is no resultant force
• 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

  Use a trolley on a track pulled by weights, measure acceleration and plot force vs acceleration graph
• Newton's third law


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


  Distance travelled before reacting to something
• Braking distance


  Distance travelled while braking
• Doubling speed


  Quadruples braking distance
• Momentum


  Measure of how hard it is to stop an object, calculated as mass * velocity
• Calculating momentum in a collision

  Total momentum before = total momentum after
• Recoil is an example of conservation of momentum
• Force


  Rate of change of momentum
• Energy


  Cannot be created or destroyed, only converted between different stores