Newton's First Law of Motion in your Car

Newton's First Law of Motion states that an object at rest will stay at rest, and an object that's moving will stay in motion at the same speed and in the same direction unless a force acts upon it. Simply put, something that's moving will keep moving unless something stops it: If you leave it alone and nothing touches it, it will just keep going the same way it's going. On the other hand, if something's sitting still in one place and nobody touches it, it will just keep sitting there. This is sometimes called the law of intertia.

You can see Newton's first law in action if you take a cup of water and put it into a cup holder in a car. As the car moves, the water in the cup is carried along with it. But starting the car from a stopped position will create an unbalanced force: The water wants to stay still, but the car is now moving, so the water has to move, too. If the cup is full enough, the water might spill. When the car stops, the water will want to keep moving forward, meaning that it might spill again.

When you are riding in a car or a truck, the law of inertia applies to you, too. In fact, the law of inertia is the reason people get hurt in car accidents. If a car is moving and then suddenly runs into something, like a wall or another car, that thing acts as an unbalanced force that stops the car abruptly. Since seat belts are part of the car, anyone in the car will also have their motion stopped abruptly if they're wearing a seat belt. A seat belt that's buckled snugly helps you to share the same state of motion as the car. When the car goes faster, the people also go faster, but when the car goes slower, the seat belts hold the people against their seats, helping them to also go slower.

If people don't wear seat belts, they aren't held in place in the car, so they can move on their own instead of sharing the car's motion. This means that if the car is suddenly in a crash, the car will stop, but the people inside will keep moving forward until they hit something that stops them. That something can be the seat in front of you or the dashboard of the car. If the crash is violent enough, the people inside can even keep going through a window, not stopping until they hit the ground or another solid object outside. When this happens, they are seriously hurt, sometimes badly enough to die.

People of all ages should wear seat belts every time they drive or ride in a car or truck. When people are killed in car accidents, a lot of times, it's because they weren't wearing seat belts. You may think that an air bag would be enough to save you in an accident, but that's not true. Although air bags can be helpful in accidents sometimes, the force of an air bag inflating can actually hurt you if you're not buckled with a seat belt. Air bags are designed to work with seat belts, not alone. It's also important to make sure you're wearing a seat belt correctly. If you're not wearing it the right way so that it fits and is snug, it might not protect you in an accident.

Car seats are designed to protect babies and young kids from being hurt in accidents by making sure that they're buckled in safely. Car seats need to be installed the right way, facing backward for babies and children who weigh less than 35 to 40 pounds. Bigger children can face forward, but they still need a car seat or booster seat to make sure that they're buckled in safely until they're big enough for an adult seat belt to fit them.

Learn more about Newton's first law and seat belt safety by visiting these websites:

Written By: Edson Farnell | Email |

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