Bernoulli's Principle

Question 1

Bernoulli's principle states that where a fluid moves faster, its pressure is:

Accepted Answer

Lower — Faster fluid flow corresponds to lower pressure.

Question 2

The lift on an aeroplane wing occurs because air moves:

Accepted Answer

Faster over the top, giving lower pressure above — Faster air over the curved top lowers the pressure above, producing lift.

Question 3

When you blow air between two hanging sheets of paper, they:

Accepted Answer

Move together — Fast air between them lowers the pressure, so outside pressure pushes them together.

Question 4

Bernoulli's principle is a consequence of the conservation of:

Accepted Answer

Energy — Bernoulli's principle follows from energy conservation in a flowing fluid.

Question 5

In the relation P + ½ρv² = constant, if v increases then P must:

Accepted Answer

Decrease — To keep the sum constant, a larger ½ρv² requires a smaller P.

Question 6

A spray gun (atomiser) works because fast air flow creates:

Accepted Answer

Low pressure that draws liquid up — Fast air over the tube lowers pressure, drawing liquid up to be sprayed.

Question 7

Air flows at 40 m s⁻¹ over a surface and 20 m s⁻¹ under it (ρ = 1.2 kg m⁻³). The pressure difference ½ρ(v₁² − v₂²) is:

Accepted Answer

720 Pa — ½ × 1.2 × (40² − 20²) = ½ × 1.2 × (1600 − 400) = ½ × 1.2 × 1200 = 720 Pa.

Question 8

Which of these is NOT explained by Bernoulli's principle?

Accepted Answer

An object floating in water — Floating is explained by Archimedes' principle, not Bernoulli's.

Question 9

When a fluid flows through a narrow section of a pipe, its speed increases and its pressure:

Accepted Answer

Decreases — Higher speed in the narrow section means lower pressure there.

Question 10

A roof can be lifted off in a storm because fast wind over the roof creates:

Accepted Answer

Lower pressure above than inside — Fast wind lowers the pressure above the roof, so higher pressure inside lifts it.