forces

• What does distance tell us?

  how far an object moves (only magnitude with no direction = scalar quantity)
• What does displacement tell us?

  the distance an object moves in a straight line from the start point to the finish point (magnitude + direction = vector quantity)
• What does the speed of an object tell us?

  the distance it travelled in a given time (scalar quantity)
• speed unit?

  m/s
• What is normal walking speed?

  1.5 m/s
• What is running speed?

  3 m/s
• What is cycling speed?


  6 m/s
• What does speed depend on?

  • age
  • terrain
  • distance travelled
• speed of cars on main road?

  13 m/s
• speed of fast train in the UK?

  50 m/s
• speed of cruising aeroplane?

  250 m/s
• speed of sound in air?

  330 m/s
• What factor can cause the speed of sound in air to vary?

  sound travels faster on warmer days
• Is the speed of a moving object constant?

  rarely
• Is velocity vector or scalar?


  vector
• is speed vector or scalar?

  scalar
• What is the velocity of an object?

  it's speed in a given direction (vector)
• If an object moves at a constant speed in a circle, does that mean its velocity is constant?

  no as its direction is constantly changing which means its velocity is also constantly changing
• What does the gradient of a distance-time graph tell us?

  the object's speed
• what speed do cars travel at on a main road?

  13 m/s
• What speed do cars travel at on the motorway?

  30 m/s
• to accelerate from a main road to the motorway what is the typical acceleration involved?

  2 m/s2
• what force would accelerating from the main road to the motorway require for a typical family car?

  2000 N
• What is inertial mass a measure of?

  how difficult it is to change the velocity of an object
• definition of inertial mass?

  the ratio of the force needed to accelerate an object over the acceleration produced
• What will an object with a larger inertial mass require to produce a given acceleration?

  a greater force than an object with a smaller inertial mass
• What is Newton's third law of motion?

  when two objects interact, the forces they exert on each other are equal and opposite
• What does the opposite force have in similarity or how is it different to the other force (3rd law)?

  it is the same in magnitude but opposite in direction
• skydiver velocity-time graph?

  .

  
• skydiver forces?

  1. initially only weight due to gravity produces downwards resultant force (accelerate towards ground)
  2. air resistance (upwards) but weight is greater so they keep accelerating downwards
  3. skydiver's air resistance increases with velocity which means no resultant force and a constant velocity (terminal velocity)
  4. parachute increases surface area and air resistance which becomes greater than weight (upward resultant force so skydiver decelerates)
  5. skydiver's velocity and air resistance decrease until they balance so velocity is constant and landing is safe for the skydiver
• What is stopping distance?

  The stopping distance of a vehicle is the sum of the distance the vehicle travels during the driver’s reaction time (thinking distance) and the distance it travels under the braking force (braking distance).
• How does a greater speed affect stopping distance?

  For a given braking force the greater the speed of the vehicle, the greater the stopping distance.
• What can increase reaction time (and thinking distance)?

  tiredness, drugs, alcohol, distractions
• What is thinking distance?

  the distance the vehicle travels during the driver’s reaction time
• What is braking distance?

  The distance a vehicle travels from the moment the brakes are applied until it comes to a complete stop.
• stopping distance=?

  stopping distance = thinking distance + braking distance
• factors affecting braking conditions?

  • road conditions (wet or icy conditions reduce friction and increase braking distance)
  • tyre quality (if tyres are more worn then braking distance increases as friction is reduced)
  • quality of brakes (if brakes are more worn then braking distance increases)
• typical value range of reaction time?

  0.2 s to 0.9 s
• methods to measure human reaction time?

  ruler
• What does kinetic energy depend on?

  velocity^2 (if velocity doubles then kinetic energy quadruples)