forces

• as height increases, density of air decreases and pressure decreases
• In a liquid, the pressure of a point increases with the height of the column of the liquid
• in a liquid, the pressure depends on weight
• pressure also depends on density, a more dense liquid has a greater weight and exerts a higher pressure
• in a column th e highest pressure is at the bottom, due to the weight
• upthrust

  force that pushes an object submerged in a fluid upward, alwasy opposite direction to weight
• size of upthrust depends on density and volume of the fluid displaced, the more dense the fluid, the greater the upthrust it will exert
• upthrust due to a difference in pressure between top and bottom, creating a resultant force
• an object travelling in a circular motion has a changing velocity, because direction is always changing, but speed may be the same
• distance time graph

  • straight line is constant speed- gradient=speed
  • slope represents magnitude of speed
  • flat line means stationary
  • a curve is changing speed
• velocity time graph

  • line increasing= increasing velocity
  • line decreasing= decreasing velocity
  • straight line is constant acceleration or decelaration
  • slope shows magnitude of acceleration- gradient=acceleration
  • flat line is constant velocity
  • area under the graph is the displacement
• acceleration is the rate of change of velocity
• instantaneous speed

  draw a tangent t o the point and find gradient
• terminal velocity

  • without air resistance, acceleration is the same (acceleration due to gravity)
  • for a skydiver= weight(gravity) and air resistance(friction)

  1. falling only force is weight
  2. acceleration
  3. increasing air resistance (resultant force decrease)
  4. acceleration decreases
  5. air resistance increases until= to weight
  6. resultant forces are zero, terminal velocity reached
  7. parachut opens= increase surface are, increase air resistance, decelerating
  8. air resistance decreases, deceleration decreasses, eventually new terminal velocity reached
• stopping distance

  brakin distance + thinking distance
• braking distance, distance travelled by a car under the braking force (deceleration)
• thinking distance is the distance travelled by a car in the time taken for the driver to react
• momentum is conserved in a closed system
• momentum is a vector quantity
• • elastic collision- collide and move in opposite directions (objects have different velocity)
  • inelastic collision- collide and move in same direction (combined mass and velocity)
• force = change in momentum/ change in time
• acceleration= change in velocity/ time
• force= rate of change of momentum
• springs may stretch, bend or compress
• hookes law

  the extension of an elastic object is directly proportional to the force applied, up to the limit of proportionality
• em spectrum

  • radio waves
  • microwaves
  • infrared
  • visible light
  • uv light
  • xrays
  • gamma rays
• electromagnetic waves

  transveres waves that transfer energy from the source of the waves to an absorber
• em waves properties

  • can travel through a vacuum
  • transverse
  • all travel at same speed in vacuum
• em spectrum-

  long on left, short on right

  • long wavelength, low frequency, low energy (less harmful)
  • short wavelength, high frequency, high energy (high ionisation- more harmful)
• red- longest wavelength

  violet/blue- shortest wavelength
• waves entering a medium

  more dense- slow down, move towards normal

  less dense- speed up, move away from normal