When a vehicle crash with another object - a tree, a wall or another moving vehicle, for example - it is stopped suddenly by the impact. However, anything is not at a standstill inside the vehicle, they will keep moving, including the passengers. This happens because of INERTIA. Inertia is an object's tendency to keep moving until something else works against this motion.
Suppose that you're driving at a steady 50 miles per hour. Your speed and the car's speed are pretty much equal, so you feel like you and the car are moving as a single unit. But if the car were to crash into a telephone pole, it would be obvious that your inertia and the car's inertia were independent. The force of the pole would bring the car to an abrupt stop, but your speed would remain the same. Your face might hit the windshield, the steering wheel or the back of the seat in front of you. Your ribcage might hit the dashboard. You could even be thrown from the vehicle. Your internal organs will still keep moving. Your brain would be compressed towards the front of your skull, and your heart, lungs and kidneys could smash into each other or into bone. It sounds horrible, and that's why we wear seat belts. Seat belts are designed to hold you into the car and spread the destructive force of the impact over the more resilient parts of your body, increasing your chances of avoiding death or serious injury in a crash by up to 50 percent.
However, seat belts are designed for adults. They go across your middle and over the shoulder, applying most of the stopping force to your ribcage and pelvis. For a seat belt to do this effectively it must fit correctly, and on a small child the seat belt is simply the wrong size to do the job. Instead, a specifically designed child car seat should be used. Using a car seat is the best way to protect kids when traveling by car. Child safety seats can greatly reduce the risk of a potentially fatal injury, especially for babies but also for toddlers.
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