Road safety
Vehicle design features
Car brakes apply an unbalanced force, causing deceleration (negative acceleration). This is due to Newton鈥檚 first law: object will continue at a constant speed in a straight line unless acted on by an unbalanced force.
Car brakes don鈥檛 apply force to occupants, so occupants will continue at the original speed in the original direction. Eventually occupants will collide with something which applies an unbalanced force. Seatbelts and airbags increase time of collision, which is the time of the occupant鈥檚 deceleration.
Size of deceleration decreases because \(unbalanced\,force = mass \times acceleration\) Size of unbalanced force decreases because \(F = ma\)
Crumple zones work in the same way. Usually located at the front of the vehicle, they are designed to absorb the impact through controlled deformation. This increases the time over which the total force from the change in momentum is applied to an occupant.
Braking distance
Braking distance is how far a vehicle travels from moment brakes are applied until complete sto
Force is applied by the vehicle鈥檚 brakes in opposite direction to motion. The force of friction between tyres and road is also applied in the direction opposite to motion.
These produce unbalanced force in the opposite direction to the vehicles (forward) motion, thus causing the vehicle to decelerate \(F = ma\) (a negative)
Mass of vehicle also affects braking distance - extra mass, like when the car is full of occupants or towing another vehicle, will require more braking distance.
The speed the car was travelling before braking begins affects the time to brake and distance travelled. There's also the road conditions which when wet or icy will affect the time to brake and distance travelled until stop.