Anyone that has ridden in a car knows that when the driver speeds up quickly, you are pressed back into your seat, and that when the driver brakes quickly, you are pushed forwards. But what would you think if the force that pushes you backwards was pushing something else forward at the same time?
For this experiment, you will need:
- a helium balloon
- an automobile
Sit in the back seat, so that you will not disturb the driver. Be sure to fasten your seat belt. Hold the balloon by the string, so that it floats but does not hit the ceiling. As the car is driving along, watch the balloon and pay attention to what you feel.
As the car speeds up, you will feel a force pressing you back into your seat. That force is called inertia. Inertia causes things that are sitting still to remain still until something pushes or pulls on them. It also causes things that are moving to continue at the same speed and direction until something pushes or pulls on them. When your car speeds up, you don't. At least not at first. The car seat pushes against you, speeding you up too. But what happened to the balloon? When inertia seemed to be pushing you backwards, the balloon was pushed forward!
Now notice what happens when the car slows down suddenly. When the driver hits the brakes, the car slows down, but you do not. You continue to move forward until something (hopefully your seat belt and not the dashboard) slows you down. Is the balloon thrown forward too? No, it is thrown BACKWARDS!
What is going on here? Lets think about it. The balloon floats because it is filled with helium, which is lighter than the air around it. The heavier air pushes the lighter balloon upwards. Now, what happens when the car speeds up? Inertia seems to push everything towards the back of the car. Again the heavier air pushes the lighter balloon in the opposite direction, and it moves forward. When you hit the brakes, the heavier air moves forward, pushing the balloon backwards.
You can do the same thing with hot and cold air. Back in the days when I worked at the Memphis Pink Palace Museum, we used large vans to carry school groups to local caves and fossil sites. In the summer, the air conditioner would not cool the entire van. Instead, the front people froze while the people in the back would sweat. Whenever they would begin to complain, I would speed up a bit, forcing the cold air to the back and the lighter, warmer air to the front.
Have a wonder-filled week.
