Ultimate Guide to Car Physics and Safety

Ultimate Guide to Car Physics and Safety

The earliest cars were made without any regard to aerodynamics or safety. Nobody ever thought about the possibility of a high-impact crash and how the passengers would be affected. So, there weren't seatbelts, airbags, or any of the other safety features that we take for granted today. However, safety is a top priority for car manufactures now. Let's take a look at the physics behind car safety features and how they help protect us.

Frame and Construction

When cars crash, the severity is calculated by looking at the impulse. The impulse is a measure of the change in momentum — the more smashed the car, the higher the impulse. This is where we get car impact ratings. Car manufacturers perform tests that involved head on crashes to study the impulse and improve the structure of the car.

  • Cars crunch to reduce impulse.
  • Car frames protect passengers.
  • Head on crashes have fewer fatalities.
  • Airbags were invented as a result.


The main purpose of airbags is to reduce injuries caused by head-on crashes. During a crash, airbags are triggered by a chemical reaction involving Sodium Azide (NaN3). Here is why they are important:

  • Airbags spread force over a large area.
  • Airbags decrease force on the body.
  • Airbags protect the head from injury.
  • Airbags inflate instantly.


Seatbelts protect passengers from injuries. They were one of the first safety features to be introduced, but didn't become standard until the late 1950s. Then, buckling up became the law in 1983. Here is why seatbelts are important:

  • You don't get projected from your car during a crash.
  • Your face is less likely to hit the windshield in a crash.
  • Seatbelts protect you from the effects of gravity and inertia.
  • Seatbelts make airbags more effective.


During a car crash, your body stays in the same position, but your head is thrown backwards at an even greater speed — that's Newton's Law. Headrests were invented to catch the head. Here is why headrests are important:

  • Headrests reduce the severity of whip-lash injuries.
  • Headrests protect the neck and head from injury.
  • Headrests make passengers more comfortable.
  • Headrests can be adjusted to accommodate any passenger.

Brakes and Tires

Brakes and tires help cars stop effectively to prevent crashes. When the brakes are applied, friction slows down the tires. Of course, in a quick stop, there some sliding friction occurs, which is where skid marks come from. The force literally tears part of the rubber off a car's tires. Here is why brakes and tires are important:

  • Anti-lock brakes help cars stop quickly on slippery roads.
  • Tires help grip the road.
  • Brakes control the speed of a car.
  • Tires wear out every 50,000 miles.

As you can see, physics plays a major role in how cars are designed. It is how car manufacturers study a car's safety and try to improve it. Car manufacturers are constantly looking for new ways to improve safety. For instance, some newer safety features include sensor monitor cameras that automatically brake cars that are about to hit something.

Further Resources

Teen Drivers: Fact Sheet

What Are Optimal Cars for Teen Drivers?

Defensive Driving Tips

Teen Driving Information and Statistics

Driver Education Toolkit

Parent-Teen Driving Agreement

Technology and Safe Driving

Car Safety Quiz

Young Drivers and Alcohol: Statistics