Fast Fact:
At speeds in excess of 370 km/h (230 mph), a one-second delay in the pits will cost a driver the equivalent of the length of a football field.
Objective:
The students will investigate the directions of positive and negative accelerations.
In the Film:
You see Michael Andretti and Mario Andretti bringing their Indy cars quickly around tight turns. Acceleration presses the drivers into their seats. The cars wheels bite into the tarmac as they leap toward the straightaway. Each car must reach its top speed before the next turn.
Background:
Acceleration is the measure of how quickly a car can change its speed. A cars acceleration is directly related to the forces that act on the car. The friction of the tires on the pavement, the movement of air around the car, and the action of the powerful motor are all reflected in the cars acceleration.
Materials:
A jar with a lid, tape and water.
To Do:
Have the students half fill the jar with water, screw on the lid, and make a line around the water level as a reference. Next, they are to place the jar on a flat surface in a car, bus, wagon or other moving vehicle. Instruct them to note the movement of the waters surface when the vehicle accelerates, slows down, turns, stops, and moves at a constant speed (fast and slow). Ask them to record the direction the surface moves in for each event. This direction represents the direction of acceleration. Have them notice in particular when the surface in the jar is flat. See if they can explain the movement of the surface when the vehicle turns. Does it indicate acceleration? If so, which direction is it in? What does this suggest is happening to the fluids inside the driver as he or she accelerates?
Whats Going On?
The water in the moving vehicle does not accelerate until there is a force acting on it. The water moves up the jars wall on the side opposite the direction of acceleration. When the vehicle decelerates, the water again moves up the wall of the jar, on the side opposite the direction of acceleration. (NOTE: Deceleration is negative acceleration.) Similarly, during a turn, the water will move up the wall of the jar on the side opposite the direction of acceleration. (NOTE: The direction of acceleration in a turn made at a constant speed is exactly toward the center of the turn.)
Taking It Further:
Have the students calibrate the device used in this experiment. One way is to tape a scale to the jar, which will allow the relative sizes of acceleration to be compared. Ask the students to explore relative accelerations, for example, car versus bus and person versus bike.