Drag

Question 1

What are the 2 forms of flow?

Answer 1

1. Turbulent flow
2. Laminar flow.

Question 2

What is the definition of turbulent flow?

Answer 2

Flow in which the velocity at any point varies erratically. Turbulent flow seperates late and less pressure is accumulated.

Question 3

What is the definition of laminar flow?

Answer 3

A type of fluid flow in which fluid moves smoothly in individual layers or streams. Laminar flow separates early and more pressure is accumulated.

Question 4

What are the 3 forms of drag?

Answer 4

1. Form drag.
2. Surface drag.
3. Wave drag.

Question 5

What is form drag?

Answer 5

Form drag is the resistance created by the pressure differential between the front and the back of an object moving through a fluid.

Question 6

What are the 2 methods to reduce form drag?

Answer 6

1. Decreasing the cross-sectional area of the body.
2. Changing the shape of the object to make it more streamlined.

Question 7

Describe an example of form drag.

Answer 7

The shape of a cyclist’s helmet is tapered towards the back to delay the separation of the air particles travelling over the helmet.

Question 8

What is the boundary separation layer?

Answer 8

The point at which the boundary layer of fluid passing over the body separates from the surface.

Question 9

List 2 examples of boundary layer separation.

Answer 9

1. Dimples in golf balls.
2. Roughness on the sides of a cricket ball.

Question 10

Explain why golf balls with dimples travel further than smooth golf balls. (Describe boundary separation in golf balls as an example)

Answer 10

Golf balls have dimples to delay the boundary layer separation point. The later the boundary layer separation, will reduce the turbulent pocket of low pressure at the back of the ball. This means the ball will travel further. A smooth gold ball will have a laminar flow moving over the ball. Laminar flow separates early from the ball causing greater pressure to build up therefore increasing drag and reducing the distance the ball travels.

Question 11

Describe boundary separation in the roughness on the sides of a cricket ball as an example.

Answer 11

The roughness on either side of a cricket ball creates different amounts of drag so the bowler can use this to produce movement. Due to the pressure differentials on either side of the ball, the rough side creates a more turbulent layer and the boundary separation layer is later. This increases the velocity and lowers the pressure on this side. This causes the ball to deviate to the side of lower pressure. The smooth side of the ball has an early boundary separation, increasing drag and lowering velocity.

Question 12

What is surface drag?

Answer 12

Surface drag is the friction between the fluid and the surface of a moving object. Smooth tightly fitting material will assist in decreasing drag.

Question 13

What are 4 methods for reducing surface drag by reducing the surface area?

Answer 13

1. Wearing caps.
2. Tight suits.
3. Athletes shaving down.
4. Helmets.

Question 14

What is wave drag?

Answer 14

Is the resistance formed by the creation of waves at the point where air and water contact. This drag comes from the creation of waves as an object moves through the water.

Question 15

What are the 3 methods for reducing wave drag?

Answer 15

1. Improving buoyancy (wearing a wetsuit)
2. Making the body more streamlined.
3. Improving technique of the swimmer (increased kicking to enhance buoyancy)