physics

• Speed distance time topic

  Key equations:

  D = speed x time

  speed = distance / time

  time = distance / speed
• Formula triangles do not count, you must write out the full equation to get the mark
• Calculating speed from a distance-time graph


  Distance / Time
• The car is stationary when the distance remains constant
• Calculating acceleration from a velocity-time graph

  Final speed - Initial speed / Time
• Calculating distance travelled from a velocity-time graph

  Split into triangle, rectangle, triangle areas and add
• The equation linking velocity, acceleration and distance is v^2 = u^2 + 2as
• Constant velocity


  Velocity that does not change
• Average speed


  Distance moved / Time taken
• Distance travelled is given by the area under the velocity-time graph
• Acceleration is given by the gradient of the velocity-time graph
• The equation linking acceleration, change in velocity and time is a = (v-u)/t
• The equation linking average speed, distance and time is average speed = distance / time
• Weight is given by the equation weight = mass x gravitational field strength
• Weight vs Mass


  • Weight depends on gravity, mass does not
  • Weight has units of Newtons, mass has units of kilograms
• Types of force


  • Contact forces: Normal reaction, Friction, Air resistance
  • Non-contact forces: Magnetic, Electrostatic, Gravitational, Nuclear
• Normal reaction force


  Force perpendicular to the surface an object is resting on
• Friction


  Force between two objects sliding past each other
• Air resistance/Drag


  Force on an object moving through a fluid (air)
• Magnetic force


  Force experienced by magnetic materials in a magnetic field
• Electrostatic force


  Force experienced by charged particles in an electric field
• Gravitational force


  Force experienced by masses in a gravitational field
• Weight


  Downward force on an object due to gravity
• Upthrust


  Upward force on an object immersed in a fluid
• Nuclear force


  Strong attractive force between protons and neutrons in a nucleus
• Force is measured in Newtons
• Force diagrams show the size and direction of forces acting on an object
• Balanced forces


  Two forces of equal size acting in opposite directions on an object
• Balanced forces mean an object will not speed up or slow down
• Nuclear force


  Strong attractive force between the protons and neutrons within the nucleus that helps hold the nucleus together
• Force diagrams show objects moving with arrows representing the size of the forces
• Balanced forces


  Two forces acting on an object in opposite directions, with the same size
• When forces are balanced

  An object standing still will stay stationary, and an object moving at a constant speed will continue at that speed
• Unbalanced forces


  One force is larger than the opposing force, causing an object to accelerate or decelerate
• Forces acting on a car

  • Driving force from the engine
  • Air resistance (drag)
  • Friction between tires and road
  • Weight
  • Normal reaction force
• Terminal velocity


  The constant speed reached when the upward air resistance force equals the downward weight force
• Mass is measured in kilograms, force in Newtons, and acceleration in meters per second squared
• Investigating terminal velocity


  1. Measure time taken to fall a set distance

  2. Calculate speed using distance/time

  3. Repeat to find average speed

  4. Compare to terminal velocity
• Hooke's Law


  The force required to stretch a spring is proportional to the extension, up to the elastic limit
• Momentum is conserved


  Momentum before an interaction equals momentum after