# Physics Assignment

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• Published : January 8, 2011

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Safety devices used in cars

i) Obtain a photograph of a car that illustrates three safety technologies and label the technologies on the photograph

ii) Investigate three different technologies that have been implemented in cars or along roads to avoid or reduce the effect of collisions. In your investigation explain how the technology works in terms of physics laws and theories.

1. Crumple zone
The purpose of a crumple zone is to increase the amount of time it takes for a car to come to a stop after being hit by an object. Crumple zones cause the force to be spread out over a long period of time, reducing the impact that the passengers in the car feel. Crumple zones today are usually made of fibreglass or steel and works during a collision by turning energy into mostly thermal and sound energy, leaving a little kinetic energy from the initial impact of the collision. Without a crumple zone, if a car were to hit a wall, the amount of kinetic energy that the car exerts on the wall, would be almost equal to the amount of energy that the wall pushes on the car. Newton’s second law states that the force of an object is equal to its mass times its acceleration. With the use of crumple zones and other safety devices in cars, a person’s acceleration in a collision can be significantly lowered. Newton’s third law states that for every action there is an opposite an equal reaction. When a car collides with another object, the inertia inside the vehicle causes everything to move at the same speed as it was before the collision. If there are no crumples, the passengers would feel the same impact as the car feels when a collision occurs. Through the use of crumple zones, the reaction force is reduced, by turning the kinetic energy into alternate forms. The crumple zones allow to spread the impact over a large area of the car which decreases the amount of pressure exerted on a specific part of the car as smaller amounts of pressure are felt throughout the vehicle rather than in one place. Crumple zones when are totally smashed have been more effective in the accident because the energy from the impact has been absorbed properly and have kept the passenger safe from the impact.

2. Seatbelts
Seatbelts help to apply the stopping force needed and spread the force around some of the strongest parts of your body such as ribcage and pelvis, rather than in specific spots such as the head if they were to fly through the windscreen of the car. The reason why a person would fly out of their seat in the first place is due to inertia, which is the tendency of a body at rest to remain at rest or of a body in motion to stay in motion unless acted on by an outside force (Newton’s law.) Therefore the seatbelt prevent s you from flying through the windscreen. The seatbelt is made of polyester and is extremely strong although the webbing that is in the seatbelt is quite flexible. The webbing material is connected to a retractor mechanism. This mechanism, which has a spring built into it applies a rotating force known as torque to help extend and retract the seatbelt. When a person pulls on the seatbelt, the mechanism turns the spring in the opposite direction causing it to resist the pulling force and pull back keeping the seatbelt snug against the person’s body. A seatbelt has a locking mechanism. When a car comes to a sudden stop, the pendulum and weight swing forward causing the top of the pendulum to get jammed between the teeth in the gear and spool that the belt is wound on. Once the person leans back into their seat again, the pendulum resumes its normal position and the seatbelt is able to extend and retract. The use of a seatbelt reduces the stopping distance of a person by up to five times compared to a person who doesn’t wear a seatbelt. The impact of force applied is decreased by a larger stopping distance, since there is little room in a car to safely slow down before hitting the windshield, the stretch...