# How can physics improve car safety?

Jun 6, 2017

refer below

#### Explanation:

Back when cars were first manufactured, cars were designed in a way that the bonnet was made of thick and strong metal. In an event of a car crash, the bonnet was made to withstand the impact and in some instances, only be slightly damaged. This meant the car looked good as new which was impressive, right?

However, that meant the driver and passengers were for sure to be critically injured or even crushed beyond recognition.

In physics term, Impulse $= F \cdot t$ . Impulse is by definition, the change in momentum. When a car crashes into a solid wall, momentum is conserved (external forces such as friction or air resistance is negligible in a short span of time) on impact till the car stops moving.

Therefore, impulse $= F \cdot t$.
Impulse $= {m}_{c a r} \cdot \Delta {v}_{c a r}$
Impulse$= 1000 k g \cdot 2 m {s}^{-} 1$ (Estimate a car to be 1 ton)
Impulse$= 2000 k g m {s}^{-} 1$

Estimate of time for car to stop is 0.5 seconds.

Impulse $= F \cdot t$
$2000 = F . 0.5$
$F = 4000 N$

As the bonnet cannot be crumpled, it will be pushed back and 4000N of force will completely crush the rest of the car.
As you can see, the smaller the time for the impact, the larger the force experienced by the driver.
To protect the driver, the time of collision has to be increased, given impulse is unchanged, to reduce the force on the driver.

Modern cars have bonnets that have crumple zones, which completely crumples in a crash. The front of the car will be completely destroyed, but the driver have a higher chance of surviving.

It is against the law to not put on seat belts in most countries. As explained above, seat belts can save lives.

Air bags are also deployed to extend the time of collision.