In most countries, kids are not allowed to drive a car until they are at least 15 or 16 years old for fear of dangerous car accidents. But for those who want to hit the road early, there is a way to drive before getting a license. They can drive bumper cars ! These mini cars can be found at amusement parks. And they are completely kid-friendly. But there is a question: Why are you allowed to drive a bumper car but not a real car? To answer this question, we have to explain what happens when there is a bump (碰撞). There are many things that can influence the result of it. Two main factors (因素) are speed and weight. Remember, speed is connected to how much energy something has. A bumper car with higher speed has more energy than a bumper car with lower speed. When you and your bumper car speed up to 5 miles per hour (usually 3 to 5, very slow) and collide with another car, both cars are sent backward from the point of the bump. You'll feel a bit of a jolt (震动) as your body is continuing to travel at 5 miles per hour while your car has stopped. If the difference in speed is much greater, the jolt can be more painful and can even put you in danger. Weight is also a factor. On a normal road, there are big cars and small ones. How far you bump a car or how far you get bumped depends on the weight of your car and the weight of the other car. This weight includes the weight of the car plus the weight of anyone in the car. I'm sure you have an answer to the question above now. Learning about how bumper cars work can help you understand not only why they're safe, but how differences in speed and weight can affect safety on the real road.