# The Physics of Car Crashes: Experimental Write Up

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• Published: October 17, 2006

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Aim

The aim of this experiment is to determine the most effective way of preventing injuries during car crashes through simulation of an actual crash.

Background

Australian statistics show that in 1993, 1956 people died and 22154 people were admitted to hospital from motor vehicle accidents. This trend has continued until the present date and is costing us not only in lives but money too. Australia spent \$6.1 billion dollars as a result of motor vehicle accidents in 1993.

Deaths from motor vehicle traffic accidents have declined from 27 per 100,000 population in 1973 to 11 in 1993. The introduction of compulsory seat belt legislation has played a major role in reducing the motor vehicle traffic accident death rate. However, motor vehicle accidents remain one of the main preventable causes of death in Australia. This shows the importance of researching and developing safety features on road vehicles. Australia simply does not have to lose this many lives and this amount of money on something that can be so easily prevented.

Developing safety features requires basic knowledge of physics so I will explain some key terms in this experiment;

Force

This is an influence on an object, tending to produce a change in movement, shape or other effects. Force can be calculated by multiplying the mass of an object (in kilograms) by it's acceleration (in metres per second per second). It is commonly written as F=ma. In this experiment, the force at which the car hits the wall must try to be reduced by simulating safety features.

Velocity

This is the rate of speed of an action or occurrence. Velocity indicates both speed and the direction in which the object is traveling. It can be calculated by dividing the distance travelled (in metres) by the time it took to reach that distance (in seconds). It is commonly written as v = s/t. In this experiment, the car's velocity will have to decrease in order to decrease the force of the impact.

Momentum

This is a quantification of the tendency of an object with a velocity to maintain that velocity. Momentum can be calculated by multiplying the object's mass (in kilograms) by the object's velocity (in metres per second). It is commonly written as p=mv. It is important to recognise that in this experiment the ball bearing will have a certain momentum and will have a tendency to remain at the velocity the model car was going before it stopped. This will impact on how far the ball bearing goes forward and therefore represent how far the driver will go forward and risk injury.

Inertia

This is the tendency of an object to maintain its state of motion. The greater the mass of an object, the greater it's inertia, thus the more force needed to change its motion. This is relevant to this experiment as the force at which the car must stop against the hard surface will somewhat depend on it's inertia.

Impulse

This is a measure of the change in an object's momentum over time. Impulse can be calculated by force (in Newtons) multiplied by time (in seconds) equalling the final momentum minus the initial momentum (in kilograms per metres per second). This is written as Ft = P2-P1. However, since p=mv the equation can be expanded to Ft = mv-mu. As momentum is something that cannot be altered as the car's mass stays the same, and therefore the impulse itself (represented as Ft) must remain the same, the only way to decrease the force is to increase the time it takes for the car to come to a stop when it hits the wall.

Deceleration

The rate of the decrease of velocity or to slow down, it can also be known as a negative acceleration. Deceleration can be calculated by subtracting the initial velocity from the final velocity (in metres per second) and dividing it by the time (in seconds) it took to go from the initial to the final velocity.

In a car crash, the person is subject to inertia while they are travelling and this is one of the reasons that car accidents cause...