4.4 Fluid Mechanics

Question 1

What is fluid mechanics?

Answer 1

The study of an object or body that travels through any liquid or gas.

Question 2

Define drag force

Answer 2

A force that acts in opposition to motion

Question 3

What are the 2 types of drag?

Answer 3

1. Surface drag
2. Form drag

Question 4

Define surface drag

Answer 4

Friction between the surface of an object and the fluid environment.

Question 5

Define form drag

Answer 5

The impact of the fluid environment on a object. Forces affecting the leading edge of an object increases form drag. Forces affecting the trailing edge of an object reduces form drag.

Question 6

What factors affect drag?

Answer 6

• the velocity of the moving body
• the cross sectional area of the moving body
• shape/surface characteristics of the moving body

Question 7

How does velocity affect drag?

Answer 7

The greater the velocity of a body travelling through a fluid, the greater the drag force. Streamlining the body helps to reduce drag.

Question 8

Define streamlining

Answer 8

Shaping a body so it can move as effectively and quickly through a fluid as possible.

Question 9

How does the cross-sectional area affect drag?

Answer 9

A large cross-sectional area increases drag. It can be reduced by crouching low when cycling .

Question 10

How does the shape/surface characteristics affect drag?

Answer 10

A more streamlined, aerodynamic shape reduces drag. For example, tight clothing, specialised helmets, air ducts, shave hair, to create a smooth surface.

Question 11

What is the Bernoulli principle?

Answer 11

Where air molecules exert less pressure the faster they travel and more pressure when they travel slower.

Question 12

What happens when a discus is thrown? (Bernoulli principle)

Answer 12

It experiences an upward lift force during flight. This enables the discus to stay in the air for longer, therefore increasing horizontal distance travelled.

Question 13

Define lift force

Answer 13

Causes a body to move perpendicular to the direction of travel.

Question 14

When is lift achieved?

Answer 14

When different air pressures act on an object. Air that travels faster has a lower pressure than air that travels slower. This is the Bernoulli principle. When a projectile is released, the angle of attack is important.

Question 15

Define angle of attack

Answer 15

The tilt of a projectile relative to the air flow

Question 16

Explain the angle of attack

Answer 16

• It changes the flow of air around the object so the air that travels over the top has to travel a longer distance than underneath.
• This means the air above travels at a faster velocity, therefore creating a lower pressure. This lower pressure above creates an upward lift force.

Question 17

What happens if the angle of attack is too great?

Answer 17

Lift is reduced and drag increases, causing the discus to stall.

Question 18

What’s the optimum angle of attack for a discus?

Answer 18

Between 25 and 40 degrees

Question 19

How does the Bernoulli principle describe a downward lift force?

Answer 19

• Speed skiers, cyclists, racing cars
• They need to be pushed into the ground so a greater frictional force is created.
• The air travelling over the top travels a shorter distance, slower velocity and higher pressure.
• This creates a greater frictional force so the tyres maintain a firm grip on the track.

Question 20

Define turbulent flow

Answer 20

Where the fluid undergoes irregular fluctuations or mixing, constantly undergoing changes in magnitude and direction.

Question 21

Define laminar flow

Answer 21

Layers of fluid flow slide smoothly over one another. They undertake smooth paths or layers,