Fluid Statics and Dynamics

This lab exercise consists of several stations. Carefully record all mesurements and observations at each station and write down your ideas and explanations. Keep data, calculations, and conclusions for each section together under the title for that section. Be sure to answer any questions.

STATIC PRESSURE

  1. Stack of Concrete: Pressure is force per unit area. Weigh the cylindrical concrete plug and measure its dimensions. Find the number of concrete plugs, stacked on the flat face, that are required to produce an atmosphere of pressure (100,000 N/m2).

  2. The Hg Barometer: The pressure due to the atmosphere will support a column of mercury about 76 cm high.

    1. Record today's atmospheric pressure with the Hg barometer in cm of Hg.
    2. Convert to N/m2 using P = rgh. (Hg has a density of 13.8 gm/cm3.)
    3. Express the pressure in lb/in2 using the conversion in your text.
    4. Calculate the column height expected today for a water barometer?

  3. Dry Snorkeling: Your lungs draw air in by expanding the chest and thus creating a pressure differential between the lungs and the outside. You can measure the maximum pressure differential of your lungs by submerging yourself in water and finding the maximum depth at which you can breath through a snorkel tube. The dry version of this experiment is to draw a column of water up a tube using your lungs. Find the maximum pressure difference, in atmospheres, of your lungs using the tube and water reservoir. (Be sure to use only your lungs, not the pump action of your mouth.)

  4. Vacuum:

    1. Turn on the vacuum pump to remove the air from the bell jar and record what happens to the various objects inside.
    2. Connect the hose from the pump to the Magdeburg hemispheres and evacuate the air inside. Try to pull the hemispheres apart without twisting.
    3. Noting that the vacuum inside the sphere is about 1/2 of an atmosphere, estimate the force needed to pull them apart.

  5. Standpipes: Observe the levels of water in the standpipes. Can you offer an explanation as to why the water is higher in the smaller pipes?

BUOYANCY

  1. Archimedes Principle: Weigh the rock and the small empty displacement jar using the spring scale. Completely fill the large container with water and place the small displacement jar below the pouring lip. With the spring scale, carefully lower the rock into the large container such that the water flows into displacement jar. With the rock not touching the container, record the scale reading. Find the weight of the displaced water. Use your data and calculations to confirm Archimedes Principle? If there is a discrepancy, explain the probable causes.

  2. Floating: Try floating the various objects on the towel next to the rectangular pan containing fresh water. (Place the objects back on the towel to dry when finished.)

    1. Explain which objects float, which do not, and why.
    2. What effect might salt water have on this experiment?
    3. What if you performed this experiment of the moon?

  3. Cartesian Diver: The cartesian diver consists of an eyedropper with a bubble trapped inside. Squeeze the bottle and observe the diver. Explain what happens. Does it matter where you squeeze the bottle?

FLUID MOTION

  1. Coin in the Box: Flip the coin into the box by blowing over the top of the coin. Use a piece of paper or tape to block the airflow getting underneath and lifting the coin. Explain this trick.

  2. Card and Spool: Orient the spool such that he hole is vertical. Hold the card gently to the bottom of the spool and blow forcefully down through the hole. If you slowly remove your hand while blowing, the card will stay in place. Explain using a diagram showing the airflow.

  3. The Trapped Ball: Turn on the air blower and place the styrofoam ball just above the outlet. Gently nudge the ball and observe its stability in the airstream. It should be possible to tilt the air blower considerably without the ball leaving the airstream. Holding the ball and moving it across the outlet will allow you to feel the forces acting on the ball. Use your other hand while doing this and note the airflow both on the inside and the outside of the ball. Explain why the ball is in stable equilibrium, using a diagram showing the airflow.

  4. The Tornado: Hold the tornado device firmly with one hand at the center and the other hand at the bottom. Holding the center in place, turn the device over and swirl the water rapidly for a few seconds with the top hand. Place the device on the table (you may need to hold onto it) and describe what you see. Explain which physics principles and conservation laws might apply. Why is there a "hole" in the center? (In an actual tornado, the hole is a very low pressure area that is responsible for exploding houses!)

  5. The Siphon: Release the valve on the siphon tube and move the end of the tube to different points below the level of the water in the tank. Observe how the velocity of the water exiting the tube changes as the position changes. Hold the end of the tube at a fixed position and change the height of another part of the tube, again noting the effect on the velocity of the water exiting the tube. Explain the results qualitatively. Is there a limit to the height of the highest portion of the tube?