Forces

• When an object falls for long enough, it reaches terminal velocity as its a balance between air resistance and weight
• when an object falls, weight is higher than friction so its a higher acceleration. As speed increases, the friction increases. Friction gradually reduces acceleration until the forces are equal. The object now reaches terminal velocity and falls at a steady speed
• Newtons first law


  If the an object is stationary, it will remain stationary and if an object is moving, it will remain moving at a steady velocity
• inertia is the tendency of an object to stay stationary or stay in motion
• Newton’s second law

  the larger the resultant force, the more it accelerates (directly proportional)

  the larger the mass, the lower the acceleration

  (inversely proportional)
• force = mass x acceleration
• Newton’s third law


  when two objects interact, the forces they exert o each other other are equal and opposite
• investigating motion practical


  1. connect trolley by a string to the pulley and connect it to a hook so masses can be changed
  2. mark a start line on the trolley to ensure it’s travels same distance to the light gate
  3. releas trolley and record acceleration using light gate
  4. to vary mass, add masses on trolley and to vary force, add masses on hook
• stopping distance = thinking distance + braking distance
• thinking distance is how far the car travels during the drivers reaction time
• braking distance = how far the car travels once brakes are applied
• factors that affect thinking distance


  • speed
  • reaction time = affected by alcohol, drugs
• factors that affect braking distance


  • speed
  • weather
  • road surface
  • condition of brakes and tyres
• when a brake pedal is pushed, contact causes friction which causes work done -> transfers energy from wheels to thermal stores of brakes which increases temperature so the faster the car, the higher breaking force which earns longer deceleration
• the higher the speed, the higher the thinking distance
• braking distance increases faster as you speed up
• Change in velocity = change in momentum
• force =. change in momentum / change in time
• larger force = faster change of momentum
• cars are designed to slow people down so the smaller the rate of change of momentum, the smaller the force
• crumple zones reduce force by increasing time taken to stop
• the seat belts reduce force by increasing time for wearer to stop
• airbags reduce force by slowing you down more gradually
• momentum = mass x velocity
• in a closed system, total momentum before = total momentum after
• to do momentum calculations:


  1. calculate momentum before collision and after collision
  2. Calculate velocity of both