It's Not Enough To Get Started. You Have To Push On.(Brief Article)

Mini: OK. Now we know that we need a force to overcome a car's inertia to get it to move. Are there other forces a car must overcome to keep on moving?

Engineer: As a matter of fact, there are two forces to overcome if a car is to keep moving. Each is a form of friction, a force between two surfaces that opposes the movement of one over the other.

Merv: Give us an example of a frictional force that opposes a car's motion.

Engineer: Well, take the air through which the car is moving. It may seem strange to you, but a moving car has to overcome the frictional force built up by the flow of air around it. A moving car pushes through the air. The harder a car has to push, the more energy it will take to run the car. The shape of a car has a great deal to do with its ability to move through air without using lots of energy.

Mini: We need to design a car that will move through air as smoothly as possible. How?

Engineer: Good thinking, Mini. Look at these cars. Do you see how an older model car, with a "boxy" design, might use more gasoline than a newer, sleeker model uses?

Merv: Well, I guess we can see how the movement of air around a car might slow it down through frictional force, but you said there were two forms of friction. What's the other one?