# The Naked Scientists Forum

### Author Topic: What is the Bernoulli Principle?  (Read 3747 times)

#### Christopher Mitchell

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##### What is the Bernoulli Principle?
« on: 14/09/2008 10:59:59 »
Christopher Mitchell  asked the Naked Scientists:

My name is Chris and I frequently listen to your podcasts from the States. I'm currently studying to be a high school science teacher and had a question about Bernoulli's principle.

We use it to explain why an aeroplane gets lift and why your shower curtain seems to suck in on your while showering. My professor stated that we don't actually know "how" an aeroplane gets lift using this principle, my question is why do we not know and what exactly do we know about it?  Thank you

Chris Mitchell

What do you think?

#### DoctorBeaver

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##### What is the Bernoulli Principle?
« Reply #1 on: 14/09/2008 11:57:07 »
As far as I'm aware, we do indeed know why an aeroplane wing gives lift. It's to do with pressure differential. Or are you inferring that there is something more fundamental involved?

#### lyner

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##### What is the Bernoulli Principle?
« Reply #2 on: 14/09/2008 13:41:10 »
The Bernouli effect is not actually needed for a plane to get lift. Many wings have an aerofoil shape of cross section. This is a sort of stretched, curved tear drop. The distance across the top surface is greater than the distance across the bottom surface. As the wing goes through the air, the air which is deflected to the top surface has to go further than the air on the bottom surface in order that the two air streams come together at the trailing edge. This means that it has to go a bit faster. The Bernouli effect / principle tells us that the pressure drops as a fluid increases in speed so the pressure on top of the wing is a bit less than the pressure underneath - giving you lift.
But you don't need an aerofoil to obtain lift - a flat sheet, tilted upwards at the front will experience a vertical force as it is driven forwards through air because of the deflection of air downwards and the 'conservation of momentum'.
The only difference between the two types of wing is, I think, the drag factor. The aerofoil is particularly good at low speeds, I believe.
You can also get a plane with an aerofoil wing to fly upside down by pointing the leading edge upwards - 'beating' the aerofoil's effect.
A similar aerofoil effect happens on the sails of a yacht - their shape naturally takes up the shape when they are 'pointing' in towards the wind and will let them sail within about 45degs to the actual direction of the wind due to the Bernouli effect.

#### DoctorBeaver

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##### What is the Bernoulli Principle?
« Reply #3 on: 14/09/2008 14:06:12 »
I know there was a Bernoulli hard drive system a few years ago.

#### lyner

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##### What is the Bernoulli Principle?
« Reply #4 on: 14/09/2008 19:38:47 »
I think that was based on a low friction air bearing. (Or possibly just someone's name.)

#### DoctorBeaver

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##### What is the Bernoulli Principle?
« Reply #5 on: 14/09/2008 19:58:47 »
Sophie - from http://www.iomega.com/25years/index.html

After two years of development, the Iomega Alpha-10 Bernoulli drive launched in 1982 as the first magnetic storage product to offer built-in protection from disk crashes. Iomega’s founders employed an aerodynamic principle known as the “Bernoulli effect” to pull the Alpha-10’s flexible disk up to the drive’s read-write heads, where a cushion of air protected the heads from hitting the magnetic storage platter. The design was essentially crash-proof, and although the eight-inch diameter, 10-megabyte removable disks were massive by today’s standards, it was an impressive technological leap.
« Last Edit: 14/09/2008 20:00:36 by DoctorBeaver »

#### lyner

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##### What is the Bernoulli Principle?
« Reply #6 on: 14/09/2008 21:30:57 »
Well, you learn sunnink every day.

Didja also know that Apple's latest laptop hard drive uses an accelerometer to tell  when it is being dropped and takes the heads away quickly to avoid damage when it hits the ground.

I also heard a story about M&S(?)'s early point of sale terminals which used microcomputers with hard drives which all died very quickly. The explanation was that the till drawers used to close so often with a bang and they jarred the drives to death after a very short time.

Thank God for flash memory.

#### The Naked Scientists Forum

##### What is the Bernoulli Principle?
« Reply #6 on: 14/09/2008 21:30:57 »