momentum

• newton's first law:

  if the resultant force acting on an object is zero and:

  • the object is stationary, the object remains stationary
  • the object is moving, the object continues to move at the same speed and in the same direction. So the object continues to move at the same velocity.
• when a vehicle travels at a steady speed the resistive forces balance the driving force. So, the velocity of an object will only change if a resultant force is acting on the object.
• The velocity of a vehicle will only change if there is a resultant force acting upon it. If the driving and resistive forces are balanced then the vehicle will continue with a steady velocity
• what is inertia

  • a property of matter
  • the resistance of the object to change its motion
• The more inertia (or mass) an object has the harder it is to get that object to change its motion.
• To find out which of two objects has the most inertia:

  • Apply an equal force to both of them when they are at rest.
  • The one that has the greatest acceleration has the lowest inertia – it was easier to get it to change its motion.
• newtons second law

  The acceleration of an object is proportional to the resultant force acting on the object, and inversely proportional to the mass of the object.
• force = mass x acceleration
• newtons third law

  Whenever two objects interact, the forces they exert on each other are equal in size and opposite in direction.
• inertial mass is defined as the ratio of force over acceleration .
• inertial mass is a measure of how difficult it is to change the velocity of an object
• When a car crashes into a crash barrier, the force acting on the car and the force acting on the barrier are equal and opposite.
• thinking distance

  Thinking distance is the distance that you travel while reacting to a stimulus until you get your foot onto the brake pedal. Thinking distance depends on reaction time, but these are not the same thing.
• braking distance

  Braking distance is the distance you travel from pressing the brake pedal until you come to a stop.
• stopping distance

  Stopping distance is the sum of thinking distance and braking distance
• stopping distance = thinking distance + braking distance
• increasing the speed of a vehicle will increase its stopping distance
• When the speed of a vehicle doubles the kinetic energy of the vehicle is four times greater
• what is the typical person's reaction time

  0.2 to 0.9 seconds
• alcohol

  increases reaction time
• caffeine

  decreases reaction time
• tiredness

  increases reacction time
• distractions

  increases reaction time
• drugs

  can increase or decrease reaction times because some are stimulants and some are depressants
• speed

  increasing speed increases braking distance
• weight of vehicle

  increasing weight of vehicle increases braking distance
• icy roads

  braking distance increases due to reduced friction between tyre and road
• wet roads

  braking distance increases due to reduced friction between tyre and road
• poor brake condition

  braking distance increases
• bald tyres

  braking distance increases when wet
• When a force is applied to the brakes of a vehicle, work done by the frictional forces between the brake pads and the brake disc reduces the kinetic energy of the vehicle and the temperature of the brakes increases.
• The greater the speed of a vehicle the greater the braking force needed to stop the vehicle in a certain distance.
• The greater the braking force the greater the deceleration of the vehicle. Large decelerations may lead to brakes overheating and/or loss of control
• momentum is a vector quantity
• the momentum of an object only depends on its mass and its velocity
• momentum = mass x velocity
• momentum is a conserved quantity

  In a closed system, the total momentum before an event is equal to the total momentum after the event.
• force = change in momentum / change in time

   F=m ∆v / ∆t
• air bags

  • air bags work by increasing the time of impact
  • it takes a person's head longer to come to a stop (compared to hitting the steering wheel)
  • as the time of impact increases the force acting on the person's head decreases
• force = change in velocity / change in time