physics flashcard (swh)

• Average speed


  Distance moved / Time taken
• Finding speed on a distance-time graph


  Calculate gradient
• Acceleration


  Change in velocity / Time taken
• Finding distance travelled in a speed-time graph


  Calculate area under the graph
• Finding acceleration on a speed-time graph


  Calculate gradient
• Relationship between final speed (v), initial speed (u), acceleration (a) and distance (s)

  v^2 = u^2 + 2as
• Types of forces


  • Gravitational
  • Electrostatic
  • Weight
  • Normal reaction
  • Friction
  • Air resistance
  • Upthrust
  • Nuclear
  • Magnetic
• Scalar

  Magnitude only
• Vector

  Magnitude and direction
• Vector quantities

  • Displacement
  • Velocity
  • Acceleration
  • Force
  • Weight
  • Momentum
• Newton's 1st Law


  If forces acting on an object are balanced, the resultant force is zero. Object at rest, stays stationary. Object moving, continues to move in same direction and at same speed.
• Newton's 2nd Law


  Acceleration is proportional to resultant force, inversely proportional to mass of object
• Calculating resultant force acting along a line

  Add up all forces acting in useful direction, subtract all forces acting in the opposite direction
• Force


  Mass x Acceleration
• Weight


  Mass x Gravitational field strength
• Stopping distance


  Thinking distance + Braking distance
• Factors affecting braking distance

  • Speed vehicle is travelling
  • Mass of vehicle
  • Condition of road
  • Tyres and brakes
• Braking distance is increased by

  Higher vehicle speed, Worn brakes, Icy road
• Factors affecting thinking distance

  • Reaction time
  • Tiredness
  • Drink and drugs
• Thinking distance is increased by

  Tiredness, Driving under the influence of drink and drugs
• Terminal velocity


  Weight acts downwards, Drag acts upwards, Object accelerates downwards, Eventually weight = drag, No resultant force, no acceleration, forces are balanced, Terminal velocity (constant velocity) is reached
• Hooke's law


  The extension of a spring is directly proportional to the force applied, provided its limit of proportionality is not exceeded
• Elastic behaviour


  The ability of a material to revert to its original shape after the forces causing deformation have been removed
• If elastic limit is exceeded, material will no longer revert to original shape after the forces have been removed
• Momentum

  Mass x Velocity
• Unit of momentum

  kg m/s
• How seat belts/crumple zones/air bags prevent serious injury

  Same momentum change, But time of impact increases, Reducing force felt, Seat belt stretches increasing area over which force acts, Pressure on body reduces
• When 2 vehicles collide, they exert equal and opposite forces on each other, their total momentum is unchanged
• Force


  Change in momentum / Time
• Newton's 3rd Law


  Two objects exert equal and opposite forces on each other
• Moment


  Force x Perpendicular distance from pivot
• Increasing the moment of a force

  Increase distance, Increase force
• Centre of mass


  The point where the mass appears to be concentrated
• Power


  Current x Voltage
• Energy transferred


  Current x Voltage x Time
• Electric current


  A flow of negatively charged electrons
• Resistance increases in a filament when the temperature increases

  Positive ions vibrate faster, Inhibit flow of electrons
• Alternating current


  A current which changes direction continuously
• Direct current


  A current which flows in one direction only
• Circuit breaker


  A device which stops the current flowing in a circuit when the current is too high