Car Safety Features

• What happens when elastic materials encounter a force?

  It deforms the material
• When will the material return to its original state?

  When the force is removed
• What are most car safety features based on?

  The idea of work done/energy
• Why do we need to apply Hooke’s Law?

  To understand why certain materials are chosen for vehicles
• Seatbelts:

  • Made of slightly elastic materials
  • Stretch around the occupant
  • If you pull too hard on the seatbelt, a pre-tensioner will stop the seatbelt from extending
  • Seatbelts need replacing after an incident as they no longer obey Hooke’s Law
• Crumple Zones:

  • Made from collapsible materials, usually thin materials
  • Designed to crumple up in an accident
• Air bags:

  • The airbag will deploy quickly
  • The airbag will deflate as the person’s head hits it, so they don’t bounce off of it but slow down
• Any moving vehicle has kinetic energy
• What must we do to stop the vehicle?

  Transfer all of the kinetic energy to another type of energy
• What is interia?

  Our reluctance to stop/go/change direction
• What happens as the kinetic energy is transferred to heat?

  Brakes heat up
• How can we reduce the force on the occupants of a vehicle?

  Braking slowly over a bigger distance
• If we can reduce the force by increasing the distance it takes to transfer the energy (taking longer to stop) l, then it reduces injuries
• What happens if we take longer to come to a complete stop?

  • We increase the time it takes to reduce the velocity to zero
  • This reduces the deceleration value, which, in turn, reduces the force felt
• How can we increase the efficiency of a vehicle, and therefore make it use fuel more efficiently?


  Reduce the different resistive forces and reduce losses when moving and not moving
• How can we make a vehicle more efficient?

  Reduce:

  • Aerodynamic losses (shape)
  • Rolling distance (Tyres)
  • Idling losses
  • Interial losses
• How can we reduce aerodynamic losses?

  • Streamlining the vehicle so air can flow smoothly over the top and sides
  • Streamlining reduced air resistance (force)
  • This reduces the amount of work (done) to move it over a certain distance
• How can we reduce rolling losses?

  • Pump up tyres so less of the grippy material is touching the road
  • Pumping up tyres reduces the amount of work (done) to move it over a certain distance
  • Improves efficiency of vehicle
• How can we reduce interial losses?

  Make the vehicle lighter
• How can we reduce idling losses?

  • Newer engines have a start/stop system to cut the engine when the vehicle is idling
  • You must activate this in your car so when you stop and take it out of gear it turns the engine on
  • This improves the fuel efficiency of the vehicle (costs less/save the planet)
• What is interial losses?

  A measure of how hard or easy it is to change the motion of a vehicle. Heavy vehicles have a lot of interia due to high mass, so require much more force to accelerate/decelerate
• What is idling?

  When your vehicle has its engine running but it’s not moving