paper two

• Force


  Any push or pull
• Types of forces


  • Contact forces (when objects are physically touching)
  • Non-contact forces (like magnetism, electrostatic forces, gravity)
• Contact forces


  • Normal contact force (pushing a door)
  • Friction
  • Air resistance
  • Tension
• Force vector


  An arrow that shows the direction and magnitude of the force
• Resultant force


  The net force acting on an object when multiple forces are present
• Finding resultant force


  1. Technically adding the force vectors

  2. If forces are in opposite directions, one must be negative

  3. If forces are at right angles, use Pythagoras to find the resultant
• Balanced forces


  Forces that add up to zero, meaning the object will not accelerate
• Balanced forces = Newton's first law of motion
• Scalar


  A quantity that has magnitude but no direction
• Vector


  A quantity that has both magnitude and direction
• Scalar quantities


  • Displacement
  • Velocity
• Vector quantities


  • Weight
• Weight


  The force due to gravity acting on an object, calculated as mass * gravitational field strength
• If an object is lifted at constant speed, the upward force must equal the 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
• Hooke's law


  Force = spring constant * extension, for elastic objects
• Energy stored in a spring

  Equal to 1/2 * spring constant * (extension)^2
• Moment


  A turning force, equal to force * perpendicular distance to pivot
• Balanced moments = no rotation
• Pressure


  Force per unit area, calculated as force / area
• Pressure in liquids


  Pressure = depth * density * gravitational field strength
• Gas pressure


  Due to collisions of gas particles with surfaces
• Higher altitude = lower atmospheric pressure
• Speed and velocity


  Measured in m/s, velocity has direction
• Acceleration


  Rate of change of velocity, measured in m/s^2
• Acceleration due to gravity = 9.8 m/s^2
• Equations of motion


  Relate displacement, initial velocity, final velocity, acceleration, and time
• Newton's first law: no resultant force = constant velocity
• Inertia


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


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

  Use a trolley on a track, measure acceleration, change force, 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 a stimulus, proportional to speed
• Braking distance


  Distance travelled while braking, proportional to speed^2
• Momentum


  Mass * velocity, a vector quantity
• Momentum is conserved in collisions
• Kinetic energy is not always conserved in collisions
• Doubling your speed quadruples your braking distance because your car needs to lose all of its kinetic energy which is equal to half MV squared
• If you double the velocity, kinetic energy goes up by a factor of 4