BLOODHOUND SSC Competition - Teachers' Tips

These simple demonstrations can help teachers and parents explain the principles of lift and thrust to primary or secondary students.

Lift

Lift is probably the hardest concept in our description of aerodynamics, but the basic idea of lift can be demonstrated with a few easy experiments.

One simple experiment you could try shows how lift is created by a desk fan blowing onto a piece of paper. To demonstrate this you need to take a piece of paper and lay it flat on a desk. Then place a desk fan about 50cm away from the paper and turn it on. The paper lifts up into the air because air rushes underneath the paper and pushes it upwards.

If you now take the paper and stick an end to the desk with adhesive putty, the unstuck end of the paper raises into the air. Again, this is because air gets stuck under the paper resulting in lift. The lift is now greater because the air cannot escape as easily.

Now stick all the edges of the paper to the desk with adhesive putty. When you turn on the fan, the paper does not start to lift. This is because the air cannot get underneath the paper. Instead it moves over the paper. This is how racing cars avoid being slowed by air resistance.

You can demonstrate Lift a slightly different way by taking another piece of paper (A5 size is ideal) and holding the short edge horizontally against your lips with the rest hanging down under your chin. Now blow hard over the upper curved bit of paper and the rest of the paper will rise up into the air. You have reduced air pressure over the upper surface, and atmospheric pressure acting on the surface below pushes the paper upwards, lift! This is known as the Bernoulli principle.

You can also demonstrate the principle of Lift by taking two empty drinks cans, placing them 5 cm apart and blow a short sharp puff in between them. The cans will come together and clang instead of moving apart as you might have expected. Replace the cans and position your mouth to blow in between again. This time however remove, say, the right hand can and then blow your short sharp puff. The can will still move to the right. Imagine the can now in a horizontal position with air being puffed over the upper surface and it will lift upwards like a wing!

Air Resistance

Air resistance can be hard to understand, because it is not possible for us to see the air pressing on objects. A desk fan can be used to demonstrate air resistance to students. Children could put their hands in front of the fan and feel the air pushing back upon them. If they hold the sides of a piece of paper and push it towards the fan, they will be able to feel the air pushing back upon the paper.

The principle of air resistance can also be demonstrated with water. We can see water and so it is easier to understand how it pushes back when an object is pushed through it. If you try to push an object through a large bowl of water, you will find that the water is pushing back. The faster you try and move an object through the water, the harder the water pushes back on that object. Air acts in exactly the same way, and the air pushing back creates air resistance. Racing cars have a pointed nose and side fins (see our example page) to help them reduce air resistance. The pointed nose helps the car pierce the air and push through. This can also be demonstrated in water as a long, thin object will move through water a lot faster than a square object. This is why boats often have pointed noses. Comparing the movement through water of a plastic boat and a plastic box might help demonstrate this.