4.4 Fluid Mechanics Flashcards
What is fluid mechanics?
The study of an object or body that travels through any liquid or gas.
Define drag force
A force that acts in opposition to motion
What are the 2 types of drag?
- Surface drag
- Form drag
Define surface drag
Friction between the surface of an object and the fluid environment.
Define form drag
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.
What factors affect drag?
- the velocity of the moving body
- the cross sectional area of the moving body
- shape/surface characteristics of the moving body
How does velocity affect drag?
The greater the velocity of a body travelling through a fluid, the greater the drag force. Streamlining the body helps to reduce drag.
Define streamlining
Shaping a body so it can move as effectively and quickly through a fluid as possible.
How does the cross-sectional area affect drag?
A large cross-sectional area increases drag. It can be reduced by crouching low when cycling .
How does the shape/surface characteristics affect drag?
A more streamlined, aerodynamic shape reduces drag. For example, tight clothing, specialised helmets, air ducts, shave hair, to create a smooth surface.
What is the Bernoulli principle?
Where air molecules exert less pressure the faster they travel and more pressure when they travel slower.
What happens when a discus is thrown? (Bernoulli principle)
It experiences an upward lift force during flight. This enables the discus to stay in the air for longer, therefore increasing horizontal distance travelled.
Define lift force
Causes a body to move perpendicular to the direction of travel.
When is lift achieved?
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.
Define angle of attack
The tilt of a projectile relative to the air flow
Explain the angle of attack
- 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.
What happens if the angle of attack is too great?
Lift is reduced and drag increases, causing the discus to stall.
What’s the optimum angle of attack for a discus?
Between 25 and 40 degrees
How does the Bernoulli principle describe a downward lift force?
- 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.
Define turbulent flow
Where the fluid undergoes irregular fluctuations or mixing, constantly undergoing changes in magnitude and direction.
Define laminar flow
Layers of fluid flow slide smoothly over one another. They undertake smooth paths or layers,
