Liquid Pressure

Johnson, Leon D. H. Williams Elementary School

Objectives: To understand Pascal's Law. To understand Boyle's Law. To show that water is a virtually incompressible liquid. To understand Archimedes' Principle. Apparatus Needed: Rectangular bottle, 1 cork stopper, 2 rubber stoppers with opening in the middle, open ended glass tube, Listerine bottle, gallon jug, hammer, clear plastic dishwashing liquid bottles (Ajax or Palmolive) with tops, medicine droppers, water, food coloring, hot water bottle, 4 meters of plastic tubing, C-clamps, metal extension rods, meter stick, rope, 30 cm. square board, swing structure approximately 2 meters tall made of 2"x4" wood with 60 cm. square 3/4" plywood board at top with holes for rope drilled at corners, 4 weights (14.3 lb. exercise weights were used in this mini-teach), 20 cm.x50 cm. plywood board. Recommended Strategy:

Put glass tube through stopper. Fill rectangular bottle with
water. Place a few drops of food coloring in water. Put stopper in
top of bottle. Pass bottle around class. Have students note what
happens when the sides are squeezed. Repeat this procedure with the
Listerine bottle. Have the class note the results of squeezing this
bottle. Ask questions as to why this happened.
Fill gallon jug with water. Put cork stopper in top of the jug.
Compress the water by pounding stopper into the jug with a hammer. The
increased water pressure should cause the jug to break. Explain that
this illustrates Pascal's Law.
Show the class a Cartesian Diver model made from plastic soap
bottle and medicine dropper. Explain how to make one by filling the
bottle with water and medicine dropper with just enough water so that
head of dropper floats. Dropper should dive when bottle is squeezed.
It should return to the top when pressure on bottle is released. Let
each class member make a Cartesian Diver. Explain that Pascal's Law,
Boyle's Law and Archimedes' Principle are illustrated in the Cartesian
Fit plastic tubing through rubber stopper. Fit funnel on other
end of plastic tubing. Fill hot water bottle with water. Color water
with food coloring. Secure rubber stopper in opening of hot water
bottle so that water does not leak and stopper does not pop out. Place
bottle on top of 60 cm. square board at top of swing structure. Run
rope through 30 cm. square board. Place it on top of water bottle.
Run the rope through holes in corners of the 60 cm. square board.
Place 20 cm.x50 cm. board at end of ropes for the swing. The C-clamps
should be attached to the lab table with extension rods holding the
funnel and plastic tubing about 3 meters above the height of the hot
water bottle. Height of water in tube with board on top of water
bottle should be calibrated as point zero. Place one weight in swing.
Measure height of liquid in tube. Mark off point on tube. Continue
placing weights in swing. Record weight and height of water with each
addition. Make a graph of the weight as it changes the water height.
Have a student sit in the swing. Measure height of liquid in tubing.
Put this point on the graph. Draw a line connecting points to see if
the line is linear or curved.
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