physics all

• Distance-time graphs


  Plotting distance against time to represent the motion of an object
• Slope of distance-time graph

  Represents the object's speed (average speed = distance/time)
• Velocity-time graphs


  Plotting velocity (or speed) against time to represent the object's motion
• Slope of velocity-time graph


  Represents the object's acceleration (acceleration = change in velocity/time)
• Determining acceleration from a velocity-time graph


  The gradient (slope) of the graph at any point represents the acceleration at that point
• Determining distance travelled from a velocity-time graph


  The area under the graph represents the distance travelled by the object
• Final speed, initial speed, acceleration, and distance moved


  • Final speed = initial speed + (acceleration x time)
  • Distance moved = (initial speed x time) + (0.5 x acceleration x time^2)
• Effects of forces between bodies


  Forces can cause changes in speed, shape, or direction of an object
• Types of forces


  • Gravitational force
  • Electrostatic force
  • Friction
• Vector quantities


  Have magnitude and direction
• Scalar quantities


  Only have magnitude
• Resultant force of forces along a line


  Resultant force = sum of all forces acting along the line
• Unbalanced force, mass, and acceleration


  Unbalanced force = mass x acceleration (F = m x a)
• Weight, mass, and gravitational field strength

  Weight = mass x gravitational field strength (W = m x g)
• Stopping distance of a vehicle

  Stopping distance = thinking distance + braking distance
• Factors affecting vehicle stopping distance

  • Speed
  • Mass
  • Road condition
  • Reaction time
• Forces acting on falling objects and terminal velocity

  1. Gravity acts as the force causing the object to fall

  2. Terminal velocity is reached when the force of gravity is balanced by air resistance
• Hooke's law


  The extension of a spring is directly proportional to the force applied
• Force-extension graphs


  The initial linear region represents the elastic behaviour of the material
• Density


  Density = mass/volume (ρ = m/v)
• Pressure


  Pressure = force/area (p = F/A)
• Pressure in gases and liquids acts equally in all directions
• Pressure difference


  Pressure difference = height x density x gravitational field strength (p = h x ρ x g)
• Behaviour of gas molecules

  Gas molecules have random motion and exert a force (pressure) on the walls of a container
• Absolute zero of temperature

  Absolute zero is the lowest temperature possible, which is -273°C
• Kelvin scale of temperature


  Kelvin scale starts from absolute zero and is related to the average kinetic energy of gas molecules
• Pressure and volume at constant temperature


  Boyle's Law: p1V1 = p2V2 (pressure and volume are inversely proportional)
• Pressure and Kelvin temperature of a fixed mass of gas at constant volume

  p1/T1 = p2/T2 (Pressure-Temperature Law)
• Pressure and volume of a fixed mass of gas at constant temperature


  Boyle's Law: p1V1 = p2V2 (pressure and volume are inversely proportional)
• Gravitational force and celestial objects


  Gravitational force causes moons to orbit planets, planets to orbit the Sun, and artificial satellites to orbit the Earth
• Orbits of comets, moons, and planets

  • Comets have highly elliptical orbits
  • Moons have relatively circular orbits
  • Planets have nearly circular orbits
• Orbital speed, orbital radius, and time period

  Orbital speed = (2 x π x orbital radius) / time period
• Classification of stars according to colour and surface temperature


  • Stars can be classified into different spectral types (O, B, A, F, G, K, M) based on their colour, which is related to their surface temperature
• Evolution of stars with larger mass than the Sun

  Nebula -> Main Sequence -> Red Giant -> Supernova -> Neutron Star or Black Hole