Fast Fact:
The side tunnels of Indy cars generate so much suction that manhole covers found on temporary street circuits must be welded down so they are not sucked off when the cars pass over them.
Objective:
The students will experience the reduction of air pressure, which helps press the race car to the pavement.
In the Film:
The shape of an Indy car is carefully crafted to create high and low air pressure areas. These areas produce downforces that enhance the performance of the car and hold it firmly to the track. In the film you see researchers test Indy cars at the Cranfield wind tunnel testing center to ensure optimal aerodynamic design.
Background:
Race cars require a lot of pressure, or downforce, to hold them to the roads surface in fast turns. The Swiss scientist, Daniel Bernoulli (1700-1782), derived an equation that described the conservation of energy in a moving fluid. The equation explained the Venturi Effect, which is that less pressure is exerted in a more quickly moving fluid. In an Indy car, there are cavities under the body that channel air and make it move quickly. Air is a fluid. When it moves faster, its pressure lowers and a partial vacuum is created, pulling the car to the track.
Materials:
Scissors or a scalpel or paper knife, several small boxes open at both ends (such as the cover of a small matchbox).
To Do:
Have the students cut a small rectangular hole in the bottom side of one of the boxes. Tell them to hold a piece of paper under the hole and blow through the box. Suggest that they try holes of different sizes. Have them blow harder and softer. Help the students realize that the box is similar to a car, and the paper is similar to a road. Have them hypothesize about why the air pressure under the car would be much less than the pressure above the car.
Whats Going On?
As the air flows through the box, it has more energy in the forward direction. It exerts less pressure sideways than does the more slowly moving air underneath the paper. The lower air pressure at the hole under the box allows the greater air pressure below the paper to push the paper up to the bottom of the box.
The box is similar to the car in that the shapes of the channels under the car make air funnel quickly through the cavities that are found there. This is like the fast-moving air blown through the box. The fast-moving air creates low-pressure areas under the car, just as the air pressure is lower at the hole under the box.
Taking It Further:
1. The next time they ride in a car, the students should roll down their window just a little and leave their hand inside the car near the opening. Holding a piece of paper close to the opening would illustrate the effect more clearly, but warn them to hold it tightly lest it fly right out the window. Have them describe what they experience.
2. Ask the students to float a small ball in a sink. They should run the tap water close to the ball. Have them experiment by directing the stream of water toward different parts of the ball. When is the ball drawn into the stream, and when is it pushed away? See if the students can explain the effect by identifying the regions of lower and higher pressure.