Checklist Questions

• Speed


  Distance ÷ Time
• Average speed


  Total distance travelled ÷ Total time taken
• Instantaneous speed


  Speed of an object at a particular moment in time, calculated by drawing a straight line (tangent) that touches the curve at one point and calculating the gradient
• Distance-time graph


  • Gradient of a line represents speed/velocity
  • Steeper gradient = higher speed
  • Horizontal line = stationary
  • Upward curve = accelerating
  • Downward curve = decelerating
  • Gradient of curve at a point = instantaneous speed
• Velocity-time graph


  • Gradient of a line represents acceleration or deceleration
  • Positive gradient = acceleration
  • Negative gradient = deceleration
  • Horizontal line = constant velocity
  • Gradient of curve at a point = rate of acceleration/deceleration at that point
• Newton's 1st law (Inertia)

  An object will remain at rest or in uniform motion unless acted upon by an external force
• Newton's 2nd law


  • The acceleration of an object is directly proportional to the resultant force acting on it and inversely proportional to its mass
  • Equation: F = ma
• Newton's 3rd law


  For every action there is an equal and opposite reaction
• Newton's 1st law: Book rests on table


  • Book remains at rest because no external force is acting upon it
  • Table exerts upward force equal to book's weight, balancing force of gravity pulling it downwards
• Newton's 2nd law: Car accelerates

  • Car accelerated because a force (generated by engine) acts on it
  • Car accelerates more if engine applies greater force, accelerates less if has greater mass
• Newton's 3rd law: Person jumps off boat onto dock


  • When person jumps of boat they push down on it (action)
  • Boat pushes up on person with equal force but in opposite direction (reaction)
  • Action-reaction pair allows person to propel themselves off boat onto dock
• Weight


  • W = mg
  • W: weight
  • M: mass of object (kg)
  • G: acceleration due to gravity (9.8 m/s² for Earth)
• Forces acting on falling bodies

  • Gravity (Weight): Pulls object towards Earth's centre, acts downwards, uses weight formula
  • Air Resistance (Drag): Opposes motion, increases with speed, depends on object's shape and surface area
• Terminal velocity


  • Maximum velocity falling object reaches when drag equals gravitational force pulling it downwards
  • Resultant force becomes 0 so it stops accelerating and falls at a constant velocity
  • Factors that affect terminal velocity: Mass, Shape, Density of medium it's falling through (e.g air, water)
• Drag


  • Force exerted by fluid (air or water) on an object moving through it
  • Opposes motion of object
  • Drag force increases as speed of object increases
  • Large surface area = more drag because there is more area for fluid to push against
  • Denser fluid (e.g water) exert more drag compared to less dense fluid (e.g air)
• In a vacuum of space where there is no atmosphere, there is no drag to oppose motion and objects are only influenced by gravitational forces
• Speed variation during skydive

  1. Free fall stage: Only force is gravity, speed increases rapidly

  2. Terminal velocity stage: Drag balances gravity, speed is constant

  3. Parachute Deployment stage: Drag and lift increase, speed decreases rapidly
• Effect of position on falling objects

  • Spread out position: More air resistance due to larger surface area, increases drag and slows descent
  • Compact position: Less drag due to smaller surface area, reduces drag and allows faster descent
• Order of planets going outwards from sun

  • Mercury
  • Venus
  • Earth
  • Mars
  • Jupiter
  • Saturn
  • Uranus
  • Neptune
• The order of the planets is primarily determined by their distances from the sun, which is a result of how the solar system was formed from a rotating disk of gas and dust 4.6 billion years ago
• Historical models of the solar system

  • Geocentric model: Ancient astronomers believed Earth was at centre of universe and all celestial bodies orbited around it
  • Heliocentric model: Believed that sun was centre of universe and all planets (including Earth) orbited around it
  • Kepler's laws: Planets move at elliptical orbits with Sun at one focus, sweep out equal area at equal times, move faster when close to the sun, square of orbital period proportional to cube of semi-major axis
• Forces acting on stars and planets to keep them in orbit

  • Gravity: Mutual attraction between objects with mass, holds planets in orbit around sun
  • Centripetal force: Directed towards centre of rotation, keeps objects moving in circular path, provided by gravitational pull of sun
  • Inertia: Newton's 1st law, keeps planets moving along orbital paths balanced by gravitational force
• Gravity assist


  • Technique used in space exploration to change speed and direction of spacecraft without using additional fuel
  • Involves spacecraft flying close to a planet/moon and using gravity from that celestial body to alter trajectory and velocity
• How gravity assist works


  • When spacecraft approaches a planet it is pulled by planet's gravity
  • As it swings around planet, it gains energy from planet's motion around sun
  • This interaction can speed up or slow down spacecraft and change its direction depending on path relative to planet's motion
• Linking gravity assist to Newton's laws of motion


  • Newton's 1st law (inertia): Spacecraft continues in its state of motion unless acted upon by external force (gravitational pull of planet)
  • Newton's 2nd law: Change in velocity (acceleration) depends on gravitational force and mass of spacecraft
  • Newton's 3rd law (action and reaction): Planet exerts equal and opposite gravitational force on spacecraft