Bernoullis Principle - Revision history

imported>Stwikiadmin at 18:23, 1 December 2016

2016-12-01T18:23:42Z

← Older revision		Revision as of 18:23, 1 December 2016
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	{\| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right"		{\| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right"
	\| [[Physics]], [[Engineering]]:		\| [[Physics]], [[Engineering]]:
	\| Pressure, Bernoulli's Principle		\| Pressure, Bernoulli's Principle, Lift
	\|-		\|-
	\| Grade Range:		\| Grade Range:
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	== Additional Information ==		== Additional Information ==

			* This demonstration can also be used to show the ''Coandă Effect'', or the tendency of a fluid jet to follow an adjacent flat or curved surface. When the ball is suspended in the air, you can show that some of the moving air is traveling along the ball's surface by having the ribbon stick held directly in front of the ball. Some of the ribbons will wrap around the bottom of the ball, following the air stream!
	* This is not a typical "hands-on" demonstration, since the blower should not be operated by non-presenters. However, it does go over well at Science Fairs and Festivals!		* This is not a typical "hands-on" demonstration, since the blower should not be operated by non-presenters. However, it does go over well at Science Fairs and Festivals!
			* This demonstration pairs well with the [[STAHP]], the [[Marshmallow Smashies]], and the [[Magdeburg Spheres]] demonstrations
	* This demonstration is a part of the [[Pressure Show]].		* This demonstration is a part of the [[Pressure Show]].

imported>Stwikiadmin: /* Why This Works */

2016-12-01T18:15:37Z

Why This Works

← Older revision		Revision as of 18:15, 1 December 2016
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	===Short Explanation===		===Short Explanation===

	Bernoulli's Principle states that if you have an object inside of a fluid, then the object will move to the part of the fluid that exerts the least amount of pressure upon it. To understand what this means, we first look at the beach ball. ~~Typically~~, the air is still around the ball, so the air exerts ~~air pressure~~ on all sides ~~of it equally~~. Because it is equal on all sides, the net force will cancel out, ~~meaning that~~ the only ~~thing left affecting~~ the ball ~~is the force of gravity~~. ~~If we use~~ the blower, ~~however, then~~ the air above the ball is no longer ~~pushing straight down on it.~~ instead~~, that air is now moving sideways~~. The air under the ball is not moving~~, though~~, and it ~~is going to push~~ the ball upward~~, against~~ the force of gravity. The '''''~~lift~~''''', or upward force, ~~is stronger than the force of gravity, so~~ the ball ~~stays suspended in~~ the moving air.		'''''Bernoulli's Principle''''' states that if you have an object inside of a fluid, then the object will move to the part of the fluid that exerts the least amount of pressure upon it. To understand what this means, first look at the beach ball. Before we use the blower, the air is still around the ball. This means that the ''Air Pressure'', or the force the air exerts across all sides of the ball, is equal on all sides. Because it is equal on all sides, the net force will cancel out, leaving the force of gravity as the only force on the ball and pulling it down. When the blower is used, the air above the ball is now moving. The moving air above the ball no longer pushes equally in all directions, and instead pushes mostly in one direction (forward) and weakly in the direction of the ball (downward). The air under the ball is not moving, and so the force it applies on the ball (upward) is now much stronger than the downward force of air from above ''and'' the force of gravity. The '''''Lift''''', or the net upward force, holds the ball up into the moving air stream and keeps it suspended.

	The bottle helps to get across how useful this knowledge is. Even though it has more mass to it, we can still get it to hover in the air by using this concept. The curve of the bottle's base allows it to float, much like the curve on a plane's wing will allow it to fly. A plane is able to fly thanks to utilization of this concept, along with a lot of important engineering to make the plane able to ascend, descend and turn in the air.		The bottle helps to get across how useful this knowledge is. Even though it has more mass to it, we can still get it to hover in the air by using this concept. The curve of the bottle's base allows it to float, much like the curve on a plane's wing will allow it to fly. A plane is able to fly thanks to utilization of this concept, along with a lot of important engineering to make the plane able to ascend, descend and turn in the air.
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	===Full Explanation===		===Full Explanation===

	In fluid dynamics, we can show that, If you have a fluid with velocity v moving past another fluid with a substantially lower velocity, that the amount of pressure that it exerts on any suspended objects perpendicular to its motion is lower than what the slower fluid exerts. ~~The~~ equation ~~we will look at is~~:		In fluid dynamics, we can show that, If you have a fluid with velocity '''v''' moving past another fluid with a substantially lower velocity, that the amount of pressure '''P''' that it exerts on any suspended objects perpendicular to its motion is lower than what the slower fluid exerts. This can be shown with Bernoulli's equation:

	{\| class="wikitable" style="color:black; background-color:#ddd; text-align: ~~center~~; margin: auto"		{\| class="wikitable" style="color:black; background-color:#ddd; text-align: left; margin-right: auto"
	\|Bernoulli's Equation:		\|+Bernoulli's Equation:
	\|'''~~1/2 v^2 + P/d = C~~'''		\|'''Compressible''' (Gases)
			\|'''Incompressible''' (Liquids)
	\|-		\|-
	\|'''v'''=Velocity, '''P'''=Pressure, '''d'''=Density		\|'''1'''/'''2 v<sup>2</sup>''' + ('''P'''/'''d''') = '''C'''
	\|'''C'''=Constant, in units (m/s)^2		\|'''1'''/'''2 v<sup>2</sup>''' + ('''''g'' <sub>*</sub> z''') + ('''P'''/'''d''') = '''C'''
			\|-
			\|'''v''' = Velocity \|\|'''''g''''' = Gravity
			\|-
			\|'''P''' = Pressure \|\|'''z''' = Elevation
			\|-
			\|'''d''' = Density
			\|'''C''' = Constant, in units (m/s)^2
	\|}		\|}

	In this ~~equation~~, we ~~have~~ three variables that can be changed: the velocity, the pressure and the density. ~~How those three change will correspond~~ to ~~a constant C. In our case with~~ the blower, we ~~will only be looking at two~~ of the ~~variables~~, the ~~'''~~velocity~~'''~~ and the ''~~'pressure'~~''. ~~When~~ we ~~adjust~~ the ~~velocity of the air~~, we ~~create~~ a ~~stream~~ of it which is ~~moving quickly. This stream~~ of ~~air~~, ~~since it has an increased~~ velocity, ~~must now~~ adjust either in pressure ~~or density in order~~ to ~~keep our constant C~~ the ~~same~~. ~~The~~ air ~~pressure~~ around ~~us changes easily~~, ~~whereas~~ the density of the air around us is ~~hard to adjust. This results~~ in ~~a change~~ of ~~how much~~ pressure the ~~moving stream of air applies~~ perpendicular ~~to itself~~. ~~By using this equation~~, ~~we now see that as~~ the velocity ~~of the fluid increases,~~ the pressure ~~needs to decrease in order~~ for the ~~constant to stay~~ the ~~same~~.		The Bernoulli's Equation has slightly different forms for compressible fluids, such as air and other gases, and incompressible fluids, such as water and other liquids. For this demonstration, we are looking at the form for compressible fluids. There are three variables that can be changed; the velocity (how fast the fluid is moving), the pressure the fluid is exerting externally at the chosen point, and the density of the fluid. Prior to the use of the blower, we can sample the air on all sides of the ball and show that, since it is still air, it is all at the same velocity (that is, it is un-moving) and therefore it is all equally dense, and also exerting equal pressure on all sides of the ball. It is important to note that when we are looking at the pressure exerted on the ball, we are looking at the pressure as being ''perpendicular to the direction of movement''. In still air, this is a null point to make, but it is important once we turn on the blower. In total, we can get a constant value at the end of our equation, which carries over to this next step.

			When the blower is on and aimed across the top of the ball, we now have a velocity value for our equation. The constant we found for still air is the ''same'' for this system, so to keep the equation balanced the points across the top have to adjust either the density or pressure. Remember: the pressure measured is ''perpendicular to the direction of movement''. Also, although air is compressible, and therefore the density could adjust, the moving air isn't separated from the still air around it by any walls; in other words, the moving air could only adjust in density if the still air around it ''also'' changes density. Pressure, however, is directional, and so it will be applied primarily in the direction of movement. For the forward pressure to increase, the perpendicular pressure must decrease. Therefore, the pressure value shrinks to accommodate the air velocity. Since the pressure value for the moving air is smaller, this means the net force is no longer balanced, but rather is applied upwards. This net upward force is called '''''Lift''''', and it is the reason why the ball stays suspended in the air!

	When we lift the ball into the stream of moving air, the top of the ball is placed inside of ~~the~~ high velocity, low pressure area while the bottom is still in ~~the~~ low velocity, high pressure area ~~around it~~. The fast moving air applies much lower pressure on the ball, ~~which~~ is ~~then~~ lifted into this low pressure area by the high pressure air below it. ~~However, the~~ ball cannot be lifted above the low pressure zone, due to the ''counter force of gravity''~~. The ball is experiencing an upward force of lift~~, ~~but it still is affected by the downward force of gravity. If~~ the ball rises too high in the stream, then the net force on it will point downward. Likewise, if the ball drops low, then the net force on it will be upward. This is why the ball will stay above the ground, bobbing slowly in the air stream as it gets pushed by the air all around it.		To summarize: When we lift the ball into the stream of moving air, the top of the ball is placed inside of a <span style="color: red">high velocity</span>, <span style="color: blue">low pressure</span> area while the bottom is still in a <span style="color: blue">low velocity</span>, <span style="color: red">high pressure</span> area. The fast moving air applies much lower pressure on the ball, since it is perpendicular to the direction of movement, and so it is lifted into this low pressure area by the high pressure air below it. The ball cannot be lifted above the low pressure zone, due to the ''counter force of'' '''''gravity''''', so if the ball rises too high in the stream, then the net force on it will point downward. Likewise, if the ball drops low, then the net force on it will be upward. This is why the ball will stay above the ground, bobbing slowly in the air stream as it gets pushed by the air all around it.

	This also helps us to understand one of the more tricky parts of this principle, which is that the reason why this happens is, surprisingly enough, due to the '''''Conservation of Mass'''''. We often hear the statement that it is the difference in air pressure on the sides of a plane's wings that creates lift. However, this difference is not caused directly by the shape of the wing. As a plane~~'s wing travels through the air~~, we are correct in that the air on top of the ~~wing is moving faster~~ than the air under the wing. However, this happens because the air ~~the wing travels through~~ has equal density throughout. ~~This means that you could think~~ of the ~~wing~~ of the plane cutting through the air much like a knife cutting through water. The knife separates the water as it slides through, but the water meets again right behind the knife. ~~Likewise~~, the ~~air traveling over~~ the ~~wing must re-meet~~ the ~~same part~~ of the air ~~traveling~~ under the wing~~. The top of~~ the wing ~~is designed to have a longer surface~~, the ~~air is forced~~ to ~~have a higher velocity~~, ~~and therefore exert less pressure~~ on the ~~wing~~, to ~~make~~ the ~~full trip~~ in ~~time.~~		This also helps us to understand one of the more tricky parts of this principle, which is that the reason why this happens is, surprisingly enough, due to the '''''Conservation of Mass'''''. We often hear the statement that it is the difference in air pressure on the sides of a plane's wings that creates lift. However, this difference is not caused directly by the shape of the wing. As a plane is ascending, we are correct in thinking that the air on top of the wings exerts less pressure than the air under the wing. However, this happens because the air has ''equal density throughout''. Think of the wings of the plane cutting through the air much like a knife cutting through water. The knife separates the water as it slides through straight, but the water meets again right behind the knife. If you slide the knife through the water while angled slightly upwards, you will see that the water above the knife will become turbulent as you glide the knife through, and that the knife will feel ''pushed'' towards it. This is because a plane's wings are designed to use an ''Angle of Attack'', or upward angle while having a forward velocity. This angle of attack results in the air under the wing applying ''more'' pressure than the air above the wing, and the plane having lift! When the plane then wants to descend, it needs to simply adjust the flaps on the back of the wings so the angle of attack isn't as severe. This, paired with slight deceleration, allows the plane to descend slowly to the runway. Stunt planes have flaps that can be adjust more freely, which allows them to do loops and spins in the air, and even fly upside down!

	== Additional Information ==		== Additional Information ==

imported>Stwikiadmin at 18:16, 9 May 2016

2016-05-09T18:16:12Z

← Older revision		Revision as of 18:16, 9 May 2016
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	{\| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right"		{\| class="wikitable" style="color:black; background-color:#ddd; margin-left: auto; float:right"
	\| [[Physics]]:		\| [[Physics]], [[Engineering]]:
	\| Pressure, Bernoulli's Principle		\| Pressure, Bernoulli's Principle
	\|-		\|-

imported>Stwikiadmin: /* Why This Works */

2016-03-23T18:41:28Z

Why This Works

← Older revision		Revision as of 18:41, 23 March 2016
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	===Short Explanation===		===Short Explanation===

	Bernoulli's Principle states that if you have an object inside of a fluid, then the object will move to the part of the fluid that exerts the least amount of pressure upon it. To understand what this means, we first look at the beach ball. Typically, the air is still around the ball, so the air exerts air pressure on all sides of it equally. Because it is equal on all sides, the net force will cancel out, meaning that the only thing left affecting the ball is the force of gravity. If we use the blower, however, then the air above the ball is no longer pushing straight down on it. instead, that air is now moving sideways. The air under the ball is not moving, though, and it is going to push the ball upward, against the force of gravity. The '''''lift''''', or upward force, is stronger than the force of gravity, so the ball stays suspended in the moving air.		Bernoulli's Principle states that if you have an object inside of a fluid, then the object will move to the part of the fluid that exerts the least amount of pressure upon it. To understand what this means, we first look at the beach ball. Typically, the air is still around the ball, so the air exerts air pressure on all sides of it equally. Because it is equal on all sides, the net force will cancel out, meaning that the only thing left affecting the ball is the force of gravity. If we use the blower, however, then the air above the ball is no longer pushing straight down on it. instead, that air is now moving sideways. The air under the ball is not moving, though, and it is going to push the ball upward, against the force of gravity. The '''''lift''''', or upward force, is stronger than the force of gravity, so the ball stays suspended in the moving air.

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	===Full Explanation===		===Full Explanation===
	~~'''''TO BE EXPANDED'''''~~

	In fluid dynamics, we can show that, as a fluid ~~moves in a direction~~ with a velocity v, that the amount of pressure that it exerts on any objects perpendicular to the ~~motion will decrease~~. The equation is:		In fluid dynamics, we can show that, If you have a fluid with velocity v moving past another fluid with a substantially lower velocity, that the amount of pressure that it exerts on any suspended objects perpendicular to its motion is lower than what the slower fluid exerts. The equation we will look at is:

			{\| class="wikitable" style="color:black; background-color:#ddd; text-align: center; margin: auto"
			\|Bernoulli's Equation:
			\|'''1/2 v^2 + P/d = C'''
			\|-
			\|'''v'''=Velocity, '''P'''=Pressure, '''d'''=Density
			\|'''C'''=Constant, in units (m/s)^2
			\|}

			In this equation, we have three variables that can be changed: the velocity, the pressure and the density. How those three change will correspond to a constant C. In our case with the blower, we will only be looking at two of the variables, the '''velocity''' and the '''pressure'''. When we adjust the velocity of the air, we create a stream of it which is moving quickly. This stream of air, since it has an increased velocity, must now adjust either in pressure or density in order to keep our constant C the same. The air pressure around us changes easily, whereas the density of the air around us is hard to adjust. This results in a change of how much pressure the moving stream of air applies perpendicular to itself. By using this equation, we now see that as the velocity of the fluid increases, the pressure needs to decrease in order for the constant to stay the same.

	''~~'1/2 v^2 + P/d = C'~~'', ~~where v=Velocity~~, ~~P=Pressure~~, ~~d=Density~~, ~~and C=Constant~~, ~~with units of (m/s)^2~~		When we lift the ball into the stream of moving air, the top of the ball is placed inside of the high velocity, low pressure area while the bottom is still in the low velocity, high pressure area around it. The fast moving air applies much lower pressure on the ball, which is then lifted into this low pressure area by the high pressure air below it. However, the ball cannot be lifted above the low pressure zone, due to the ''counter force of gravity''. The ball is experiencing an upward force of lift, but it still is affected by the downward force of gravity. If the ball rises too high in the stream, then the net force on it will point downward. Likewise, if the ball drops low, then the net force on it will be upward. This is why the ball will stay above the ground, bobbing slowly in the air stream as it gets pushed by the air all around it.

	~~By using this equation, we can see that as the velocity of the fluid increases, the Pressure needs to decrease in order for the constant to stay the same.~~ This also helps us to understand one of the more tricky parts of this principle, which is that the reason why this happens is, surprisingly enough, due to the Conservation of Mass. As a plane's wing travels through the air, we are correct in that the air on top of the wing is moving faster than the air under the wing. However, this happens because the air the wing travels through has equal density throughout, ~~and so~~ the air traveling over the wing must re-meet the same part of the air traveling under the wing. ~~Since the~~ top of the wing ~~has~~ a longer surface, the air is forced to have a higher velocity, and therefore exert less pressure on the wing, so to make the full trip in time.		This also helps us to understand one of the more tricky parts of this principle, which is that the reason why this happens is, surprisingly enough, due to the '''''Conservation of Mass'''''. We often hear the statement that it is the difference in air pressure on the sides of a plane's wings that creates lift. However, this difference is not caused directly by the shape of the wing. As a plane's wing travels through the air, we are correct in that the air on top of the wing is moving faster than the air under the wing. However, this happens because the air the wing travels through has equal density throughout. This means that you could think of the wing of the plane cutting through the air much like a knife cutting through water. The knife separates the water as it slides through, but the water meets again right behind the knife. Likewise, the air traveling over the wing must re-meet the same part of the air traveling under the wing. The top of the wing is designed to have a longer surface, the air is forced to have a higher velocity, and therefore exert less pressure on the wing, to make the full trip in time.

	== Additional Information ==		== Additional Information ==

imported>Stwikiadmin: /* Why This Works */

2016-03-02T20:31:03Z

Why This Works

← Older revision		Revision as of 20:31, 2 March 2016
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	== Why This Works ==		== Why This Works ==

	Bernoulli's Principle ~~States: If~~ you have an object inside of a fluid, then the object will move to the part of the fluid that exerts the least amount of pressure upon it. To understand what this means, we first look at the beach ball. Typically, the air is still around the ball, so the air exerts air pressure on all sides of it equally. Because it is equal on all sides, it will cancel out, meaning that the only thing left affecting the ball is gravity. If we use the blower, however, ~~we now have~~ the air above the ball no longer pushing down on it. instead, that air is now moving sideways. The air under the ball is not moving, though, and it is going to push the ball upward, against the force of gravity. The '''''lift''''', or upward force, is stronger than the force of gravity, so the ball stays suspended in the moving air.		===Short Explanation===
			Bernoulli's Principle states that if you have an object inside of a fluid, then the object will move to the part of the fluid that exerts the least amount of pressure upon it. To understand what this means, we first look at the beach ball. Typically, the air is still around the ball, so the air exerts air pressure on all sides of it equally. Because it is equal on all sides, the net force will cancel out, meaning that the only thing left affecting the ball is the force of gravity. If we use the blower, however, then the air above the ball is no longer pushing straight down on it. instead, that air is now moving sideways. The air under the ball is not moving, though, and it is going to push the ball upward, against the force of gravity. The '''''lift''''', or upward force, is stronger than the force of gravity, so the ball stays suspended in the moving air.

	~~When we are able~~ to, we ~~will include a few diagrams~~ in this ~~explanation~~ to ~~help visualize~~ the ~~science behind~~ it.		The bottle helps to get across how useful this knowledge is. Even though it has more mass to it, we can still get it to hover in the air by using this concept. The curve of the bottle's base allows it to float, much like the curve on a plane's wing will allow it to fly. A plane is able to fly thanks to utilization of this concept, along with a lot of important engineering to make the plane able to ascend, descend and turn in the air.

	The bottle helps to get across how useful this knowledge is. Even though it has more mass to it, and therefore more weight, we can still get it to hover in the air by using this concept. The curve of the bottle'~~s base allows it to float, much like the curve on a plane~~'~~s wing will allow it to fly. A plane is able to fly thanks to utilization of this concept, along with a lot of important engineering to make the plane able to ascend, descend and turn in the air.~~		===Full Explanation===
			'''''TO BE EXPANDED'''''

	~~A more thorough explanation:~~ In fluid dynamics, we can show that, as a fluid moves in a direction with a velocity v, that the amount of pressure that it exerts on any objects perpendicular to the motion will decrease. The equation is:		In fluid dynamics, we can show that, as a fluid moves in a direction with a velocity v, that the amount of pressure that it exerts on any objects perpendicular to the motion will decrease. The equation is:

	'''1/2 v^2 + P/d = C''', where v=Velocity, P=Pressure, d=Density, and C=Constant, with units of (m/s)^2		'''1/2 v^2 + P/d = C''', where v=Velocity, P=Pressure, d=Density, and C=Constant, with units of (m/s)^2

	By using this equation, we can see that as the velocity of the fluid increases, the Pressure needs to decrease in order for the constant to stay the same. This also helps us to understand one of the more tricky parts of this principle, which is that the reason why this happens is, surprisingly enough, due to the Conservation of Mass. As a plane's wing travels through the air, we are correct in that the air on top of the wing is moving faster than the air under the wing. However, this happens because the air the wing travels through has equal density throughout, and so the air traveling over the wing must re-meet the same part of the air traveling under the wing. Since the top of the wing has a longer surface, the air is forced to have a higher velocity, and therefore exert less pressure on the wing, so to make the full trip in time.		By using this equation, we can see that as the velocity of the fluid increases, the Pressure needs to decrease in order for the constant to stay the same. This also helps us to understand one of the more tricky parts of this principle, which is that the reason why this happens is, surprisingly enough, due to the Conservation of Mass. As a plane's wing travels through the air, we are correct in that the air on top of the wing is moving faster than the air under the wing. However, this happens because the air the wing travels through has equal density throughout, and so the air traveling over the wing must re-meet the same part of the air traveling under the wing. Since the top of the wing has a longer surface, the air is forced to have a higher velocity, and therefore exert less pressure on the wing, so to make the full trip in time.

	== Additional Information ==		== Additional Information ==

imported>Stwikiadmin at 17:27, 2 October 2015

2015-10-02T17:27:14Z

Show changes

imported>Morganp: moved Bernoulli Effect to Bernoullis Principle: Incorrect name

2015-09-04T01:44:01Z

moved Bernoulli Effect to Bernoullis Principle: Incorrect name

← Older revision		Revision as of 01:44, 4 September 2015
(No difference)

imported>Cody at 23:26, 12 September 2013

2013-09-12T23:26:07Z

← Older revision		Revision as of 23:26, 12 September 2013
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	It can easily be seen that an airplane can generate some lift or upward force due to the higher pressure on the bottom of a wing versus a lower pressure on the top. This pressure is caused by the shape of the wing, forcing the increase in velocity and decrease in pressure. Please note that it is NOT caused by the air having to travel a longer distance over the curved side in the same time interval as the bottom of the wing. The reason it is traveling faster is actually due to conservation of mass (oddly enough). Note in the image below the two different air streams. The upper stream constricts as it flows over the airfoil. Due to conservation of mass laws, the air must increase its velocity over the airfoil and thus, by Bernoulli's Principle, exerts less pressure on the top of the wing. Conversely, the lower stream expands causing the air velocity to decrease and thus increasing the pressure.		It can easily be seen that an airplane can generate some lift or upward force due to the higher pressure on the bottom of a wing versus a lower pressure on the top. This pressure is caused by the shape of the wing, forcing the increase in velocity and decrease in pressure. Please note that it is NOT caused by the air having to travel a longer distance over the curved side in the same time interval as the bottom of the wing. The reason it is traveling faster is actually due to conservation of mass (oddly enough). Note in the image below the two different air streams. The upper stream constricts as it flows over the airfoil. Due to conservation of mass laws, the air must increase its velocity over the airfoil and thus, by Bernoulli's Principle, exerts less pressure on the top of the wing. Conversely, the lower stream expands causing the air velocity to decrease and thus increasing the pressure.

			== Why it is ==

	== Real Life Examples ==		== Real Life Examples ==

	Airplanes, car spoilers, hydrofoils, inside carburetors		Airplanes, car spoilers, hydrofoils, inside carburetors

imported>Stwikiadmin: Created page with "== Age == Elementary School, Middle School, High School == Format == Stage Show, Hands-on == Materials == Blower Blower hose Electrical Extension cord Beach ..."

2013-09-11T14:14:31Z

Created page with "== Age == Elementary School, Middle School, High School == Format == Stage Show, Hands-on == Materials == Blower Blower hose Electrical Extension cord Beach ..."

New page

== Age ==

Elementary School, Middle School, High School

== Format ==

Stage Show, Hands-on

== Materials ==

Blower
Blower hose
Electrical Extension cord
Beach Ball
2-liter pop bottle, empty (with rounded bottom)
2-liter pop bottle, with some water (with rounded bottom)
Roll of one-ply toilet paper
Wooden Dowel (with fringe on one end)

== Safety Precautions ==

Science Theatre demonstrators must keep the safety of themselves and their audience in mind at all times. All Science Theatre demonstrators must have read through the Safety Training page. The ST Safety Box with first aid kit, fire extinguisher, etc. should always be available to demonstrators. Always wear safety gloves, glasses, and a labcoat if handling chemicals; always perform potentially dangerous demonstrations at a safe distance from the audience; and always keep a very close eye on any volunteers you call from the audience. Make sure objects are not blown into the audience.

== Preparation ==

Obtain all the materials listed above. Attach the blower hose to the air output of the blower. Ensure the blower has power and is operating correctly. Inflate the beach ball. Have on hand the two 2-liter pop bottles (one w/ water one w/o water). Have on hand the wooden dowel and toilet paper.

== Demonstration ==

Part 1: Turn the blower on low power and while holding the hose at a sharp upward angle, find the position at which the beach ball will float. The wooden dowel can be used to show the moving air as the fringe will point in the direction of air flow. Notice the moving air on top of the ball, but no moving air under it. The dowel can also be used to show that there is nothing holding the ball in the air (ie. hidden strings, etc.)

Part 2: Continue to demonstrate the principle as demonstrated in part 1, but this time use the empty 2-liter bottle.

Part 3: Continue to demonstrate the principle as demonstrated in part 1, but this time use the 2-liter bottle with water in it. At this time it also works best to have the blower on high power.

Part 4: Place the toilet paper roll on the wooden dowel and hold the toilet paper in front of the blower (on high power). The toilet paper will begin to unravel and fly off the roll. This can be directed into the audience if desired.

== What to Say ==

Part 1: Ask the kids if they think you can make the beach ball float in the air. Allow them to answer, then continue on to demonstration part 1. Explain that the air is moving faster on the top of the ball then on the bottom of the ball and that this means there is less pressure on the top and more pressure on the bottom. This causes lift and the ball stays aloft. Be sure to show the moving air on the top versus the still air on the bottom by using the fringe end of the wooden dowel.

Part 2: Start demonstration part 2. You can re-iterate the general concepts that you described in part 1, again showing the moving air versus the non-moving air. Again, explain that the fast moving air creates low pressure.

Part 3: Start demonstration part 3. Ask the kids if they think you can make a 2-liter pop bottle float if it has water in it and is heavy! Allow the kids to answer. Show the kids that it is in fact possible to make the water weighted bottle float. Remember to use the higher blower setting. You can again explain what is happening (high velocity = low pressure = lift). Be excited that the lift is strong enough to hold the bottle up!!!!

Part 4: Start demonstration part 4. Tell the kids that you are going to do something fun with Bernoulli's Principle. How about making a HUGE streamer of toilet paper!!!! Start by blowing the streamer to the side of the stage and then you can slowly move the paper so it is directed over the audience;. if desired. The paper is light and harmless so there is no inherent danger in this demo.

An airplane's wing forces air to move very quickly over the top of it. Therefore the pressure of the air above the wing is lower than the air below the wing, by Bernoulli's principle - so airplanes can fly!

Why It Is: This simplistic explanation of Bernoulli's Principle stems from Bernoulli's equation which states that the sum of all forms of energy in a fluid flowing along an enclosed path is the same at any two points in that path. This means that a change in pressure will cause a change in velocity. This is demonstrated by an airplane wing, where the change in pressure due to the curved surface changes the velocity at which the air flows because the sum of the velocity and pressure must be a constant.

1/2*Velocity2 + Pressure/Density = Constant

The above equation shows that as the pressure increases, the velocity must decrease in order to keep the sum truly a constant. It can also be said that as the velocity increases, the pressure must decrease in order to keep the sum at a constant. The above equation excludes the (gravity x height) term that should be included in the sum.

It can easily be seen that an airplane can generate some lift or upward force due to the higher pressure on the bottom of a wing versus a lower pressure on the top. This pressure is caused by the shape of the wing, forcing the increase in velocity and decrease in pressure. Please note that it is NOT caused by the air having to travel a longer distance over the curved side in the same time interval as the bottom of the wing. The reason it is traveling faster is actually due to conservation of mass (oddly enough). Note in the image below the two different air streams. The upper stream constricts as it flows over the airfoil. Due to conservation of mass laws, the air must increase its velocity over the airfoil and thus, by Bernoulli's Principle, exerts less pressure on the top of the wing. Conversely, the lower stream expands causing the air velocity to decrease and thus increasing the pressure.

== Real Life Examples ==

Airplanes, car spoilers, hydrofoils, inside carburetors