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A Car That Drives Itself

Bird Navigation & Mapping

Recycling the Trabant

Curing the Storm in the Head

Flight of the Dragonfly
in the classroom


Imagine a car that could drive itself in an emergency. As you'll see on FRONTIERS, researchers at Mercedes are working on this idea right now. They've developed a van that can take over for the driver -- even at 150 mph on the German autobahn. Knowing the "science of driving" does not guarantee safety on the road, but it may help drivers understand some of the challenges associated with controlling a vehicle.

Curriculum Links
Activity: As the Wheel Turns: The Physics of Driving



nervous system

graphing, slope

motion, velocity



A quote to share with your students before tackling this activity:

"Some concepts of physics are intuitive. We already know what will happen, but we can't always explain it in scientific terms."

-Harry West, Associate Professor of Mechanical Engineering at MIT

Discover how knowledge of simple physics could make you a better driver. Form small groups to discuss the driving situations described below. First, explain how you would answer each question in everyday language. Then, brainstorm with your group to develop a scientific explanation based on your knowledge of physics. Not sure about your physics? Try elaborating from your initial common sense explanation of the situation and use the diagrams to help work out your ideas.


QUESTION: Why should you drive slowly in rain or snow?

A. First explanation (in everyday language): The road surface is slippery and you could lose control.

B. Second explanation (based on physics): Water and snow reduce the friction between the tire and the road. Loss of friction results in the loss of braking and steering control.
  1. When changing a tire, why is it hardest to loosen the lug nut on the bottom?

  2. Why do vehicles with underinflated tires use more fuel than those with properly inflated tires?

  3. In case of sudden impact, why does a passenger in the car fly forward if not restrained by a seat belt?

  4. Why should you slow down when approaching an unbanked curve? Use a diagram to help you figure out what will happen if you don't slow down.

  1. A. The bottom lug nut is bearing most of the weight of the car.
    B. The downward force of gravity on the car's mass creates pressure on the lug nuts. This pressure increases with the distance from the top of the car. Therefore, the lug nut in the bottom position has the greatest pressure applied to it.

  2. A. Underinflated tires make the wheels more difficult to turn.
    B. Underinflated tires can wobble from side to side, producing more friction. Because the frictional force has increased, more energy must be expended to overcome it. Also, as the wheel turns, it is constantly deforming the underinflated tire from round to flat, requiring more energy than if properly inflated.

  3. A. The passenger is still moving at the same speed as the car before impact.
    B. A body in motion will resist the negative acceleration of the car. Newton's First Law states that an object in motion tends to continue in motion at constant speed in a straight line unless acted upon by another force.

  4. A. If you are moving too fast around a curve, your tires will skid.
    B. When you approach an unbanked curve at a constant speed, your velocity will change because your direction will change. This requires acceleration toward the center of the curve or centripetal force. The centripetal force is provided by the sideways friction between the tires and the road. The faster the forward motion, the more centripetal force is needed. When you are traveling too quickly around a curve, the centripetal force needed is greater than your tires can provide and the car will begin to skid.

CREDIT: Tim Yanka, former science curriculum coordinator for Central Bucks School District in Doylestown, PA, teaches science at Holicong Middle School in Buckingham, PA and is a very safe driver. This activity is his first contribution to FRONTIERS.


Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.