An outline of notes without explanation. To paraphrase what Fermat once scribbled in a margin, the explanations are elsewhere. A concept of discovery science is that the class thrashes out explanations. Better to not cover all of these and give the class some time to ponder the science.
Gear
Albezia sticks
balloon balance
balloons
blower/air cleaner
folder
glass
newspaper
paper
ping pong ball
string
tape
water jug
Newton's third law
For any force a counterforce occurs: balloon rocket. Note that the surface of the balloon provides pressure that drives the air out the back of the primitive rocket. Use this as a lead in to the air pressure activities below.
Pressure
How many sheets to hold down a stick?
Obtain some Albezia lebbeck sticks or other snappable wood.
Place a stack of newspaper on the table.
Ask the class how many sheets of newspaper are sufficient to hold down the stick so that it can be broken in half with a chop of the hand.
Demonstrate that a single sheet is sufficient.
Demonstrate what happens without the sheet. Wear safety glasses and ensure that no one is within a 45° angle down strike. The wood will likely launch up and out like a one way boomerang.
Discuss. Do not simply explain. Discuss why. To the extent possible remain in a Socratic dialog mode.
Albezia, being round and rough, does not work as well as a thin flat pine yardstick. Increasing the surface area of the Albezia by using a forked stick or pre-halving the stick may help.
Pressure equals the force per unit area. For an equal application of force, a smaller area exerts a higher pressure due to the inverse relationship for the area.
Solving for the force indicates that larger areas produce more force for a constant pressure.
Defying gravity with water: pressure is all around us
Cut out a piece of manila folder or other suitable material.
Fill a drinking glass with water.
Place the paper over the open end of the glass.
While holding the paper, invert the glass.
Release the paper.
Discuss. Do not simply explain. Discuss why. Note that this might only work in Kitti.
Occasionally a student will postulate that air in the glass would cause the demonstration to fail. Having some air in the glass does not cause the demonstration to fail. Demonstrate this as necessary. This works with really tall containers. For a bigger mental impact use a larger container.
The arc of a water spout
Find a container into which three holes can be placed. Bigger is better, more fun, and messier. A five gallon water container that has already developed a leak is useful. Ask at the local water company. Patch any hole that interferes with the demonstration.
Put three holes into the side of the container vertically. If need be, cover the holes with tape. Keep a "tape tab" so the tape can be easily removed.
Ask the class to sketch or otherwise describe the path the water will make.
Fill with water.
Remove the tape tabs.
Discuss. Do not simply explain. Discuss why. What is the shape of the water arcs? How does pressure vary with depth?
Balloon balance
Connect two balloons via a valve. This may take the most prep. Current unit consists of a stop cock valve for 3/4 inch PVC pipe with two short lengths of clear plastic tubing that snug fits into the PVC valve. Two brass gas nozzles are fitted into the clear plastic pipes. Electrical tape is used to add necessary thickness to the brass gas valves to hold on the balloons. All parts were found at a local hardware store. In the past needle valves used for fish tank air systems have been used, lots of electrical tape is needed to build up the small tubing so as to keep a balloon attached.
Inflate one balloon and attach to one side of the valve with the valve closed.
Under inflate a second balloon and attach to the other side.
Ask the class to predict what will happen when the valve is opened.
Open the valve.
Discuss. Do not simply explain. Discuss why.
Bernoulli
Why planes fly
Cut out a long strip of paper.
Place under your lip.
Blow.
Discuss. Do not simply explain. Discuss why.
Magic floating balloon
Use a blower that blows up.
Put a balloon in the air column.
Discuss. Do not simply explain. Discuss why.
Curve ball
A curved plastic toy ball slinger.
A ping pong ball.
Throw. By now the students are used to ducking for cover. Best done outdoors!
Discuss. Do not simply explain. Discuss why.
Later: two balloons hanging from a stick
Hang two balloons on strings from a stick so they are a few inches apart.
