Fluid mechanics- lift

Question 1

What is the Bernoulli principle?

Answer 1

• The Bernoulli principle is where air molecules exert less pressure the faster they travel and more pressure when they travel slower.

Question 2

The Bernoulli principle further…

Answer 2

• The Bernoulli principle relates to how a lift force is generated.
• A lift force can be both in an upward and downward direction.
• If the lift force is in an upward direction, it will keep an object in the air for longer, therefore increasing its horizontal displacement.
• If the lift force is in a downwards direction, it will force an object towards the ground, therefore increasing the amount of friction generated with the ground.

Question 3

How does lift work?

Answer 3

• Lift is achieved when both low and high pressures act on an object.
• High air pressure comes from slow air.
• Low air pressure comes from fast air.

Question 4

Generating a lift force

Answer 4

• A lift force is achieved when an object is tilted into the air flow.
• When an object is tilted it changes the flow of air around the object.
• If the air has to travel further due to this change, it will increase in velocity.
• This increase in air velocity leads to lower low air pressure.

Question 5

A02- cyclists

Answer 5

• With cyclists, the low streamlined body position over the handle bars means that the air that travels over the top of the cyclist has a shorter distance to travel than the air underneath.
• This results in the air above the cyclist travelling at a slower velocity which therefore creates a higher pressure.
• The higher pressure above the cyclist creates a downward lift force and allows the tyres of the bike to maintain a firm grip on the track.