Learning Objectives 1.To look at both Passive & Active car safety systems 2.To explain how the active safety systems work in terms of the Physics we know 3.Essential preparation for exam & research task! The Physics of Car Safety

Passive Car Safety Systems Passive car safety systems aim to help you avoid accidents through: 1.Good ergonomic design (e.g. Not having to take your eyes off the road & hands off the wheel to use the radio 2.Allowing the driver to concentrate to the maximum of his ability, by keeping him comfortable & avoiding distractions

2 Example Passive Car Safety Systems Radio controls on the steering wheel Paddle gear controls on the steering wheel

Additional Passive Car Safety Systems 1.Electric Windows 2.Smart adaptive cruise control 3.Adjustable seating 4.Adaptive headlights 5.Automatic lights & wipers 6.Lane departure warning 7.Parking sensors 8.Tyre deflation warning 9.Sleep warning

Active Safety Active Safety protect the occupants when a crash occurs and include : 1.Crumple zones, Safety cages & impact absorbing bumpers 2.Safety belts 3.Air Bags 4.Traction Control & Stability systems 5.ABS brakes (Anti-Lock Brakes) 6.Collapsible steering columns 7.Side impact bars 8.Head restraints

Active Safety Crumple zones, Safety Cages & impact absorbing bumpers Aim to absorb energy & to dissipate it away from the passenger compartment. Reduce the forces on the passenger by “making the crash take a longer time” Safety belts Restrain passenger, prevent ejection & limit impact with dashboard etc. Absorb energy by stretching &“make the crash take a longer time”. Since they stretch they must be replaced after an accident.

Active Safety Air bags Avoid direct impact between head/chest & steering wheel/dashboard. Spread the impact, absorb energy and “make the crash take a longer time”. Only operate for significant crashes since explosive nature carries its own risk Traction Control & Stability Systems Prevent the wheels from slipping/spinning during hard acceleration on slippery surfaces. Helps the driver maintain control.

Active Safety ABS Brakes (Anti-Lock Brakes) ABS brakes prevent skidding in the event of sudden emergency braking. Electronics monitor the wheels & briefly release the brakes if the wheels lock. This allows the driver to maintain full control and continue steering hopefully avoiding an accident.

Active Safety Collapsible steering columns Aim to avoid driver head & chest injuries by either providing minimal resistance upon impact and/or being withdrawn away on impact Side impact bars Avoid passenger compartment ingress during side impacts Head restraints Limits backwards and sideways movement of head and neck. (whiplash). Also Offers limited protection against unrestrained rear passengers, animals & luggage

The Physics of Active Safety Forces :From P3 you recall that F =ma and that a = change in speed / time Substituting : F = m x change in speed / time For a given crash, mass and change in speed are fixed. Force inversely proportional to the time taken Making the crash “take longer” dramatically reduces deceleration & hence the forces involved

The Physics of Active Safety Energy :From P3 you recall that Kinetic Energy = ½ mv 2 Increases in speed, dramatically increase the KE which must be absorbed / dissipated in event of a crash