Fluid Mechanics


Surface Tension

Submerged Float

PIRA: 2A10.15

Description: A ring with a large cork stopper attached is weighted so that it will float with the ring above the surface. When the ring is forced below the surface, it cannot rise above the surface due to surface tension.

Needle Float

PIRA: 2A10.20

Description: The surface tension of water is sufficient to float a slightly greasy sewing needle, skin oil will work.

Floating Strawberry Basket

PIRA: 2A10.22

Description: Even though strawberry baskets are more dense than water they will float because of surface tension. They will sink if they are wet and will not float again until they are completely dry.

Plate Measure of Surface Tension

PIRA: 2A10.33

Description: A round plate is lifted by a rubber band, and the rubber band stretches to a certain length. When the round plate is placed on the surface of water and lifted again, the rubber band will stretch more.

Bubble Makers

PIRA: 2A10.52

Description: A set of bubble makers to demonstrate surface tension, and discuss why bubbles are always round.

Double Bubble Paradox (Subtitle)

PIRA: 2A10.53

Description: Two bubbles are blown, one should be larger than the other. When the two are connected together, the larger bubble will get even larger. This is due to surface tension.

Capillary Tubes

PIRA: 2A20.10

Description: Show the rise of water in a small diameter tube due to surface tension.


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Statics of Fluids

Pressure Independent of Direction

PIRA: 2B20.10

Description: Thistle tubes connected to a U-tube manometer are used to determine the pressure at depth in a fluid. The thistle tube point both downward and sideways. Direction of the pressure can be discussed as one thistle tube points downward and the other points to the side.

Pascal’s Vessels

PIRA: 2B20.40

Description: These variously shaped tubes are used to show that water seeks its own level. The height of the fluid in the column depends only on the pressure to which it is exposed and not on the diameter of the column.

Hydraulic Press

PIRA: 2B20.60

Description: The hydraulic jack can be used to break scrap pieces of wood, showing that the force on the small cylinder is multiplied to achieve the larger force on the large cylinder.

Bed of Nails

PIRA: 2B20.63

1 atm Bar

PIRA: 2B30.06

Description: A steel bar that weighs 14.7 lbs and is 1 square inch in cross section demonstrates the atmospheric pressure per square inch.

Crush the Can {steam}

PIRA: 2B30.10

Description: A small amount of water is heated in a can and the can is then capped. When the can is placed in ice water, the active steam molecules are condensed as they cool, crushing the can.

Crush the Can {vacuum}

PIRA: 2B30.25

Description: A can is connected to a vacuum pump. When the air is taken out of the can the atmosphere then collapses the can.

Lift a Stool

PIRA: 2B30.50

Description: Place a square foot of 1/16″ rubber sheet on a chair and lift the chair by pulling up on a handle attached to the rubber seat.

Weigh a Submerged Block

PIRA: 2B40.10

Description: The objective of this demonstration is to show that the weight of displaced water added to the weight of the mass in the water is equal to the weight of the mass out of the water.

Weigh a mass on a scale. While still connected to the scale, place that mass in a bucket of water. Allow the displaced water to run over into a large beaker. Weigh the mass in the water. Now, weigh the displaced water. Make sure that the beaker has been weighed in advance so as to be able to know the weight of the water.

Show that the weight of the displaced water + the weight of the mass in the water = the weight of the mass outside of the water.

Finger in Beaker on Scale

PIRA: 2B40.15

Description: A finger placed in a beaker of water on a scale clearly exhibits buoyancy force.

Archimedes’ Principle

PIRA: 2B40.22

Description: Suspend a pail and a mass from a force sensor, lower the mass into the water, collect the overflow, and pour into the pail.

Cartesian Diver

PIRA: 2B40.30

Description: A plastic pipette is filled with water and air to the point of being nearly zero buoyant. The pipette is in a 2 L. plastic pop bottle filled with water. When the bottle is squeezed the air in the pipette is compressed and the diver sinks. Changes in the atmospheric pressure can make the diver rise or fall. {Make sure that it works before it is tried in front of the class.

Water / Alcohol Tubes

PIRA: 2B40.53

Description: A water barometer and an alcohol barometer are connected together across their tops. If air is drawn OUT of the system through the hose, the columns is the barometers rise. The dependence of the height of the column on the density of the fluid can be shown.

Water level Displacement

PIRA: 2B40.55

Description: This demonstration shows that a large item that floats will displace more water when it floats than when it sinks.

Buoyant Force Rotator

PIRA: 2B40.57

Description: Two large Erlenmeyer flasks on the ends of a rotating platform. In each is a float, and on one is tied a float on the outside. When it is rotated, the ball on the outside goes out from the flask and the floats on the inside go toward the center.

Density Ball

PIRA: 2B40.59

Description: A ball when placed in cold water will float, but when placed in 40 degrees C the ball sinks.

Hero’s Fountain

PIRA: 2B60.10

Description: A fountain that appears to defy the law that water can only rise to its highest level. The fountain appears because of the air space in the lower bulb.


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Dynamics of Fluids

Leaking Can

PIRA: 2C10.27

Description: This demonstrates the difference in pressure at different heights as the water will leak from the can at different rates depending on the height of the hole.

Venturi Tube

PIRA: 2C20.11

Description: Three glass tubes are connected to each other on the bottom and top so the level of fluid is the same in each. When air is blown through the upper most tube, the levels of the fluid in the tubes change to show the pressure difference. The diameter of the upper tube varies where each of the three tubes connect. When air is blown through the upper tube (across the tops of the vertical tubes) the levels of the fluid in the tubes change as the pressure for each change. The smaller diameter reduces the pressure more, so the water level would rise in the more constricted flow.

Floating Ball or Light Bulb

PIRA: 2C20.30

Description: A ball is suspended in a stream of air. The angle of the air stream can be changed from vertical to about 30 degrees while the ball remains suspended. Other objects can be floated too, light bulbs, etc.

Funnel and Ball

PIRA: 2C20.35

Description: When air is blown through the neck of the funnel, the ping pong ball will hover.


PIRA: 2C20.42

Description: Demonstrate Bernoulli effect.


PIRA: 2C20.43

Description: An airfoil, it returns to the sender when it is thrown properly.

Hanging Billiard Balls

PIRA: 2C20.46

Description: The object is to get someone to blow the balls apart by blowing between them. The harder the person blows, the closer the balls get.

Demonstration Airfoil

PIRA: 2C20.51

Description: An airfoil to show the class why airplanes fly.

Pitot Tubes

PIRA: 2C40.11
Description: These are air speed indicators.


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