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Dynamics of Fluids

  • C4-41: TERMINAL VELOCITY - BOTTLE IN TUBE

    C4-41
    An easily observable terminal velocity experiment.
    The bottle falls through the tube; close fit creates air friction, leading to a low terminal velocity. Adding water to the bottle increases the terminal velocity. Retrieve bottle quickly with string for repeated drops.
    OS0

  • D2-03: CANS ON INCLINED PLANE - WITH AND WITHOUT WATER

    D2-03
    Illustrate the effect of moment of inertia on rolling acceleration.
    Roll two identical cans from rest down an incline, where one is empty and the other is nearly filled with water. Q: Which gets to the bottom first, or is it a tie? A: The water-filled can reaches the bottom first. Due to its small viscosity, the rotation of the water is limited, and that can acts much like a body sliding without friction down the incline. Using the broom, give the two cans a push up the incline. Which can will roll higher up the incline?

  • D5-12: CORIOLIS EFFECT - WATER JET

    D5-12
    Model the Coriolis effect.
    Fill the can with water and rotate the entire can-tank assembly on its platform. The water jet exhibits a curved trajectory which is an analog to the curvature of the trajectory of a projectile on earth due to the Coriolis effect.
    OS10

  • D5-15: CYCLONE AND ANTICYCLONE MODEL

    D5-15
    Illustrate the Coriolis effect for a fluid source and sink.
    As the water tank rotates water is pumped out the bottom of the tank at a "LOW" and back into the bottom of the tank at a "HIGH." If the tank is rotated counterclockwise, the water circulation is counterclockwise around the LOW and clockwise around the HIGH, as indicated by the flags. This simulates the Coriolis effect in the northern hemisphere, which produces cyclones around low pressure areas and anticyclones around high pressure areas. Rotating the tank clockwise, simulates the effect in the southern hemisphere.
    OS3

  • F4-01: VISCOSITY OF LIQUIDS

    F4-01
    Compare the viscosities of water and mineral oil.
    Two tubes contain heavy balls in water and mineral oil, respectively. Invert the tubes and compare terminal velocities to compare viscosities.
    OS4

  • F4-02: VISCOSITY OF AIR

    F4-02
    Demonstrate that air is viscous.
    A large thin disc is suspended above a copper plate mounted on a rotator. As the plate is rotated, the thin disc begins to rotate slowly in the same direction, because of drag caused by the viscosity of the air.

  • F4-04: SILLY PUTTY

    F4-04
    Demonstrate a non-Newtonian fluid.
    Set a glob of silly putty on the stand. Slowly it "flows" over the edge. If it is formed into a ball it will bounce off the floor. Silly putty is a non-Newtonian fluid: it's viscosity increases as it is subjected to greater pressure.

    f4-04a

  • F4-05: PARACHUTE TOY

    F4-05
    Demonstrate how a parachute quickly reaches its terminal velocity.
    A toy rocket has an attached plastic parachute. The parachute is carefully, loosely folded against the rocket and they are tossed into the air together. The parachute opens and fills with air. The system soon reaches its slow terminal velocity and falls gently to the floor. Be careful not to allow the strings to become tangled or detached, as this will prevent the parachute from operating properly.

  • F4-11: LAMINAR AND TURBULENT FLOW OF AIR

    F4-11
    Demonstrate laminar and turbulent flow.
    Place the streamers near the front of the fan, and notice that they line up due to the laminar flow. Then place the streamers behind the fan or about one meter away, and note that they move irregularly due to the turbulent flow.
    F4, OS6

    f4-11a

  • F4-12: UNMIXING - GLYCERIN AND DYE

    F4-12
    Illustrate laminar flow by "unmixing" two fluids
    Glycerin forms a cylindrical shell between two plexiglass cylinders. The inner cylinder can be rotated, setting up a laminar flow in the glycerin. Using a long hypodermic syringe, blue dye is injected in a line in the glycerin midway between the two cylinders. As the inner cylinder is rotated several turns, the dye "mixes" with the glycerin. When the rotation is reversed, the dye "unmixes" and almost returns to its original state. Below is a link to the schematic of the unmixing apparatus.
    F4

  • F4-13: FLUID FLOW MODEL

    F4-13
    For use as a model in developing equations for fluid flow.
    Flow of fluid onto surface Q is given by the equation

    Q=d v dA cosa = d v dA(projection),

    where d is the density of the fluid, v is the velocity of flow, A is the vector area of the surface, and a is the angle between the surface and the flow.
    J1

  • F4-14: WIND TUNNEL

    F4-14
    Show air flow around different objects.
    Dry ice is dropped into a container of water to produce visible air flow in the wind tunnel, which is then projected using an overhead projector. Various objects can be placed in the wind tunnel, and the air flow past the objects observed.
    F4

    f4-14af4-14bf4-14c

  • F4-21: LIQUID IN SPINNING SPHERE

    F4-21
    Show the behavior of a liquid when subjected to a centripetal force.
    When the sphere is rotated, the water leaves the bottom of the sphere and forms a band in the middle of the sphere, due to the reaction to the centripetal force. Rotate sphere slowly to achieve this effect.
    F4, F1, D1

    f4-21a

  • F4-22: SPINNING WATER BUCKET

    F4-22
    Illustrate the reaction force on spinning water and the shape of the water surface.
    As the glass bucket rotates, the water surface assumes a parabolic shape. Use about 600 ml of water; rotate slowly
    F4, F1, D1

    f4-22a

  • F4-23: WATER PENDULUM

    F4-23
    Show the surface of a container of water in a swinging pendulum.
    A container with water is suspended as a pendulum. When the container is held to one side, the water moves to its lowest point and the surface remains horizontal. When it is released and swings as a pendulum, the water spreads out uniformly on the bottom of the container and stays at rest at all times.
    F4, F1, FS1

  • F4-25: CYCLONE IN A BOTTLE

    F4-25
    Illustrate vorticity in a perhaps tricky way.
    Q: What is the quickest way to get the water from one bottle into the other?

    A: Turn it upside down and give it a couple of quick rotations. This starts a circular rotation of the water, so that as it falls down into the lower bottle it stays on the outside of the neck, allowing air to rise up into the upper bottle simultaneously. Simply turning the bottles upside down will trap a small amount of air in the upper bottle and not allow more air to rise, quickly causing the water flow to cease. Tilting the bottle allows air to fill the upper bottle while water is flowing, but is not as fast as using the vortex technique.
    F4, F1

    f4-25a

  • F4-31: SIPHON

    F4-31
    Illustrate how a siphon works.
    Fill both bottles and the connecting tube with water. Raising either bottle causes water to flow from the upper to the lower beaker.
    F4, F1

  • F4-32: SIPHON - CHAIN MODEL

    F4-32
    illustrate how a siphon works.
    A bead chain passes over a pulley between two beakers. When one of the beakers is raised, the chain flows from the higher into the lower beaker, just as water flows from the higher to the lower container of a siphon. This is due the greater weight of the chain, or water, on the side of the lower container. Note that the cause of the siphon flow is not air pressure, which is greater at the surface of the lower container!

  • F4-33: PYTHAGOREAN CUP

    F4-33
    Demonstrate the siphon in a surprising way.

    This special cup is designed to force the consumer to limit his or her intake of certain beverages to a modest amount. The cup is filled so that the liquid level is below a line about one inch below the top, a reasonable drink for temperate individuals. This works out fine, and the consumer may then drink at his or her leisure. If, however, liquid is poured into the cup above the level indicated by the line, the greedy consumer receives his or her just deserts as ALL of the beverage then is siphoned out of the cup through a hole in the bottom.
    Background:

    The central shaft in the cup contains a tube that functions as a siphon. An opening low in the cup leads to a (usually hidden) tube that rises to the top of the shaft and then curves down again to exit at the base of the cup. When the fluid level in the cup rises higher than the upper curve of the tube, it can act as a siphon and drain out all of the liquid. Similar mechanics are used in some household appliances to cause them to drain when liquid reaches a maximum level.

    Despite the name, it is unclear whether the mathematician Pythagoras of Samos actually invented this device; but the earliest examples are believed to date to approximately that era (the 6th century BCE).

  • F4-34: SIPHON BALANCE

    F4-34
    Demonstrate properties of the siphon using a counterintuitive example.
    Two beakers with 600 ml of water are balanced on a platform suspended from a pivot. A siphon tube runs between the two beakers. The system is initially in equilibrium, with the platform horizontal, as seen by the arrow indicator at the center of the platform.

    The following experiments may be performed using this apparatus:

    1. What happens if extra water is poured into one of the beakers? 2. What happens if some water is removed from one of the beakers? 3. What happens if a small wooden block is placed on the platform by one of the beakers? 4. What happens if the wooden block is placed into one of the beakers so that it floats in the water? 5. What happens if an aluminum cylinder is lowered into one of the beakers so that it is suspended in the water without touching the beaker? 6. What happens if the aluminum weight is allowed to rest on the bottom of the beaker?