Fast Fact:
During practice at Indianapolis, driver Rick Mears crashed and ended up upside down. When the car came to rest safely on its protective roll-bar, the only scrapes he had were on his helmet.
Objective:
The students will investigate stability and learn to control the location of the center of gravity of an object.
In the Film:
An Indy car driver is seated low in the car, in the middle and toward the front. The car itself is close to the ground and the wheels are far apart, keeping the center of gravity low. Super Speedway was filmed from an actual Indy car. During the filming, the engineers were concerned that the large motion picture camera mounted on top of the car would destabilize the vehicle, making filming at high speeds perilous.
Background:
For an object to remain stable, its center of gravity (the balance point of an object) must remain above its base. If the center of gravity is not above the base, the object will fall over. The base of a car is the rectangle formed by the four wheels touching the ground. In a high-speed turn, the sideways forces producing the turn tend to push the center of gravity out from above the cars base. This could flip the car over. How do engineers reduce the risk of an Indy car flipping over?
Materials: Tape, 2 pieces of cardboard 15cm x 15cm (6 in x 6 in) , a protractor, 1 straw 15cm (6 in) long, 150cm3 empty milk carton, 6 metal washers.
To Do:
Following the illustration, create a ramp with two pieces of cardboard hinged together with tape. Make a ridge by taping a straw 2cm (0.8 in) above the hinge. Tape the protractor to the end of the cardboard to measure the angle at which it opens. Place the empty milk carton against the straw. Have the students slowly raise the cardboard until the milk carton falls over the straw. Record the angle. Encourage the students to experiment. They can add between one and six washers at different areas on the milk carton to see if it will tip over at lower or higher angles. Have the students determine where the washers must be placed to make the milk carton the most stable. Ask them to explain in terms of the center of gravity and base area. How do their results compare to the design of Indy cars? How would they modify a car for a race on a flat oval track with only left turns?
Whats Going On?
When the students first raise the milk carton and it falls, they discover its center of gravity. By adding weights and moving them around, they shift the center of gravity. When the washers are high up, the milk carton tips over at a smaller angle. This is because the center of gravity is also high up and therefore has shifted past the base area at a lower angle than the carton without washers. When the washers are on the bottom of the carton away from the straw, the milk carton is the most stable. The lower the center of gravity, the more stable the milk carton. Indy cars have their wheels far apart to keep their center of gravity very low. This helps prevent the cars from flipping over.
Taking It Further:
1. Ask the students to go back to the car they designed in Activity 1 and look at it in terms of its center of gravity.
2. Consider adding a sharp curve with a guard rail toward the bottom of the ramp developed for the race event in Activity 1. Use this as a testing ground for car stability. How are the various car designs affected?