Session 3: Demonstrating that drag is influenced by the smoothness or roughness of the surface

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Objective: To demonstrate that drag is influence by the type of surface

Explanation:

If we think of drag as aerodynamic friction, the amount of drag depends on the surface roughness of the object; a smooth, waxed surface produces less drag than a roughened surface. This effect is called skin friction and is usually included in the measured drag coefficient of the object.

Rough surface: produces a big amount of drag.

Smooth surface: the surface of a plane is very smooth and polished, producing a small amount of
drag.

Material:

• few tanks
• different forms: few flat plates
• an aerodynamic form very polished
• water
• emery paper with different degrees of roughness

Maximum duration:

15 minutes

Main questions to be asked:

Do you know how it feels when you touch the surface of a plane?

Why is the surface of the plane so smooth?

Introduction/Starters

Ask the students if they ever touched the surface of a plane. How was the surface?

It was rough?

It was smooth?

Main activities

If they didn’t touch before the surface of a plane (end even they did), ask them to touch the wing or the aeromodel you have in the classroom. Ask them to write why they think the surface is the way it is (smooth).

Ask the students to glue emery paper with different degree of roughness on few plates, and then to move them on a plain surface. What is their remark on this?

Which one they can move easier and witch one opposes the movement.

Conclusion / Plenary

We think of drag as aerodynamic friction, the amount of drag depends on the surface roughness of the object; a smooth, waxed surface produces less drag than a roughened surface.