Physics 1

• 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
  • Apart from centimeters and decimeters
• Converting units


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

  2. Divide by the conversion factor if a smaller number
• Prefixes in standard form

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


  • Any push or pull
  • Can be contact forces (physically touching)
  • Can be 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 must be negative

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


  • Forces add up to zero
  • Object will not accelerate, stays at constant velocity
• Scalar


  Measurement or quantity with magnitude but 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 (9.8 N/kg)
• Lifting an object at constant speed

  Upward force must equal the weight
• Work done


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


  Calculated as mass * gravitational field strength * height
• Moment


  • Turning force
  • Calculated as force * perpendicular distance to pivot
• If moments turning clockwise and anticlockwise are balanced, 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


  Distance or displacement over time
• Acceleration


  • Change in speed divided by time
  • Unit is m/s^2
• Acceleration due to gravity

  Constant 9.8 m/s^2 downwards
• Velocity-time graph

  • Gradient gives acceleration
  • Area under graph gives distance traveled
• Newton's equations of motion

  • Used to predict object's motion when accelerating
  • Involve s, u, v, a, t
• Newton's first law

  No resultant force, motion is constant
• Inertia


  Tendency for an object's motion to stay constant
• Newton's second law


  F = ma, unbalanced forces cause acceleration
• Proving Newton's second law

  Use trolley on track, measure acceleration, change force, plot graph
• Newton's third law


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


  Distance traveled before reacting to something
• Doubling speed

  Quadruples braking distance
• Momentum


  • Measure of how hard it is to stop something
  • Calculated as mass * velocity
• Calculating momentum in collisions

  Total momentum before = total momentum after
• Force and momentum


  Force = rate of change of momentum
• Energy


  Cannot be created or destroyed, only converted
• Energy stores


  • Kinetic energy
  • Gravitational potential energy
  • Elastic potential energy
• Kinetic energy


  Calculated as 1/2 * mass * velocity^2
• Elastic potential energy


  Calculated as 1/2 * spring constant * extension^2
• Energy stores


  Types of energy that an object can have