Air Bags

Air bags are fitted in cars to reduce the injury by collision with the steering wheel, dashboard or windscreen.During a collision the rapid deceleration means a rapid loss of momentum.According to Newton's second law the rate of change of momentum is proportional to the resultant force, so a rapid change in momentum requires a large impact force.During a crash, sensors detect the rapid change in velocity and initiate an explosive chemical reaction that fills the air bag with nitrogen gas in just 30ms. This provides a cushion for the passenger or driver's head and upper body. The deceleration is less rapid and so the impact force on the person is reduced.
Newton's second law states that the rate of change of momentum is proportional to the resultant force and is in the same direction.The constant of proportionality is 1 if 1 newton is defined as the force needed to give a 1kg object an acceleration of 1ms^-2