PAGE INDEX
  • PURPOSE
    		•
  • IDEAS
    		•
  • CONCEPTS
    		•
  • MATERIALS
    		•
  • INVESTIGATIONS
    		•
    1. PURPOSE: [index]
      The body or shell of a real car has several purposes. It protects the passengers from wind and rain, it provides added safety in case of a crash, and it improves how the car looks. But it also changes how the car performs because a well designed shell can reduce the force of air on the car as it moves.

    2. IDEAS: [index]
      Some ideas for shells are given below.


      Figure 1: Shell or body concepts

    3. CONCEPTS: [index]
      1. Aerodynamics
        Aerodynamics: a branch of dynamics that deals with the motion of air and other gaseous fluids and the forces acting on bodies in motion relative to such fluids. Air is a gas and produces a resistance force to objects that move through it.
        To see how much force air can have, you can try some simple experiments. While driving in a car, carefully try holding your hand flat, and sticking it out of the window. Feel how much force the air has on your hand. What happens to the force when you tilt your hand?


        Figure 2: Force of air on your hand

      2. Frontal Area
        When looking at the front of an object that is moving through the air, you can see the "frontal area" that the air must move around. The smaller the frontal area the less air has to be moved around the object so the less force is required to move through the air.
        To illustrate this concept try riding a bike down a hill, compare how fast you can go while sitting upright, or by leaning forward. If you crouch down, the air can go over you instead of hitting you in the chest, so you should be able to go faster. In other words, the force of the air on your body when you crouch down is less, so you are more aerodynamic.


        Figure 3: Bicyclist and frontal area

      3. Shaping
        The shape of the object affects the way the air goes around it. The air wants to stay in a nice smooth flow around the object, however, fast changes in shape create "holes" in the air that disrupt this flow and increase the "drag" or resistance of the air on the objects movement.


        Figure 4: Shapes and airflow

        Look at things that move through the air, and notice how they are shaped. For example the two cars shown below, notice how the air flow around them is affected by the shape.


        Figure 5: Smooth verses disrupted flow

        Fast cars are shaped so that, when moving quickly, they can move more easily through the air. As another example, you may have seen tractor-trailer trucks with big air deflectors on them. The reason for this deflector is to make the truck more aerodynamic, so the truck's engine doesn't have to work as hard and the truck driver saves money on gas.


        Figure 6: Semi truck and deflector

        In some situations, the force of air helps you instead of hurting you. For example, what if you want to slow down very fast? How about using a parachute? Or if you want to create more pressure on the drive wheels without adding weight - you could add a wing that creates a down force on the car. Now the force of the air is helping you.

    4. MATERIALS: [index]
      So how do you reduce the force of air on your solar car? One way might be to add a body or sheel to it that deflects the air around the car. Some possible materials you might want to use are:
      • Poster board
      • Cardboard
      • Foam core
      • Stiff insulation foam (Foamula)
      • Mylar or plastic sheet
      • Paper
      Insulation foam can be carved to a shape, made smooth with sandpaper, and even painted to look nice. (Warning: some paints, likes spray paint, will "melt" foam, so always try your paint on a piece of scrap foam that you don't need before using it on the real thing.)
      Radio control modeling stores also cary an acrylic that can be heated shaped over a mold of your own construction.

    5. EXPERIMENTS & INVESTIGATIONS: [index]