Bernoulli’s PrincipleBernoulli’s Principle

Created by:Created by:

Keith P. MurphyKeith P. Murphy

Winston Churchill High SchoolWinston Churchill High School

Potomac, MDPotomac, MD

Bernoulli’s Principle:Bernoulli’s Principle:• A Swiss

scientist born in 1700’s that is most famous for his work in fluid pressure.

Remember!!!Remember!!!• Air is a gas and a fluidAir is a gas and a fluid• Air pressure is due to the Air pressure is due to the

motion of its particlesmotion of its particles• ex. The quicker a stream of ex. The quicker a stream of

particles travel, the ???????particles travel, the ???????

Bernoulli’s PrincipleBernoulli’s Principle

• Pressure in a moving stream exerts less pressure than the air surrounding the moving stream Quick stream = low air pressureQuick stream = low air pressure

Slow stream = High air pressureSlow stream = High air pressure

Standing Tennis BallStanding Tennis Ball• In your notes, In your notes,

hypothesize hypothesize why the tennis why the tennis ball ‘stands’ in ball ‘stands’ in the air.the air.

• Draw the air Draw the air currents.currents.

PennPenn

AIR FLOWAIR FLOW

The AnswerThe Answer• The tennis ball is surrounded by an air The tennis ball is surrounded by an air

stream of equal speed, thus equal stream of equal speed, thus equal pressure.pressure.

• The down force is ‘G.’The down force is ‘G.’

• Thus, the ball stands onThus, the ball stands on

• air. The air pressure belowair. The air pressure below

• is equal with the ‘G’ force.is equal with the ‘G’ force.

AIR FLOWAIR FLOW

‘‘G’G’

Bernoulli & FlightBernoulli & Flight• Bernoulli’s Bernoulli’s

Principle is what Principle is what allows birds and allows birds and planes to fly.planes to fly.

• The secret behind The secret behind flight is ‘under flight is ‘under the wings.’the wings.’

•The air on top of the wing must travel a longerThe air on top of the wing must travel a longerdistance than the air below the wing. But, air ondistance than the air below the wing. But, air onboth sides must reach the end of the wing at theboth sides must reach the end of the wing at thesame time. Therefore, the air on top of the wing same time. Therefore, the air on top of the wing traveling faster = traveling faster = less air pressureless air pressure..

Creates LiftCreates Lift

AIRAIR

Below is a NASA illustration of whatBelow is a NASA illustration of whatsurface pressure is exerted on what surface pressure is exerted on what surface areas of the wing. Is this surface areas of the wing. Is this plane ascending or descending?plane ascending or descending?

This diagram shows regions of air This diagram shows regions of air pressure around specific areas of thepressure around specific areas of thewing. Again, notice that the low pressurewing. Again, notice that the low pressureregion is above the wing, allowing for region is above the wing, allowing for upward thrust.upward thrust.

LIFTLIFT

GRAVITYGRAVITY

THRUSTTHRUSTDRAGDRAG

•The engines provide The engines provide THRUST.THRUST.•The wings provide The wings provide LIFT.LIFT.•Gravity provides the Gravity provides the ‘G force.’‘G force.’•And, fluid friction provides theAnd, fluid friction provides the DRAG.DRAG.•What is happeningWhat is happeningif the airplane is if the airplane is flying at constant flying at constant altitude?altitude?

What forces are =?What forces are =?