A block of wood is "floated" in a volume of water much smaller than the volume of the wood block. The water is poured into a container the same shape, but slightly larger than the wood block, then the wood block is inserted.

In the wonderland world of the physicist, a battleship could be floated in a bathtub using one cup of water, if the tub were the right shape!

A block of dry ice is placed in the bottom of a clear plastic cylinder sealed on the bottom, trapping carbon dioxide in the bottom of the container as the dry ice sublimates (evaporates). Bubbles produced with a standard soap bubble blowing gizmo will float on top of the more dense carbon dioxide. Some carbon dioxide diffuses into the bubbles, so they get larger and sink! Some of the bubbles freeze when they sink to the bottom of the container near the dry ice. The photograph at the right is a detail of the top of the container.

It may be necessary to remove static electricity from the plastic container. A damp cloth or lit match may assist with this.

Invite students to predict what will happen as the air cools.

A flask containing vinegar is connected to a balloon containing baking soda. This system is balanced with a collection of weights on a pan balance as shown in the photograph above. The balloon is raised up so the baking soda falls into the vinegar, commencing a reaction that produces carbon dioxide and inflates the balloon. When the balloon becomes inflated, what happens to the balance? Will the balloon side go down, will the weight side go down, or will it remain balanced?

Included here are before and after pictures for this experiment using an electronic balance, showing the weight in grams and tenths (of force), eg. 261.7g down to 258.4g for the balloon expanding to a diameter of about 18cm.

Q: How will the float move inside the water vessel as the vessel executes simple harmonic motion?

A: Surprisingly, the float will remain at rest in the water vessel as it oscillates. It will even remain at rest when the vessel is stopped suddenly with your hand! See video 2 below. As the vessel oscillates, the weight density of both the floater and the water bath vary together, as the acceleration of the vessel varies, so the ratio of their densities remains the same, and they will continue to float with the same geometrical relationship!!

A: The water level will be below the black line, as seen by clicking your mouse on either of the pictures above. Notice also that the water level in the tank remains the same, at the level of the top of the black tape.

A common pre-college experiment is to burn a candle inside of a bottle which has been turned upside down over a container of water. The water supposedly rises about one-fifth of the way up the bottle, indicating that the oxygen, about one-fifth of the air in the atmosphere, has been "used up" in the combustion process.

The candle in our experiment is placed inside the sealed tube containing air above a colored water bath, and is then ignited by a hot wire (center photograph). The water level goes down initially, then returns to its original level just after the candle goes out. There is virtually NO CHANGE in the water level from before to after the experiment is performed (photograph at right).

This is the CORRECT WAY to do this experiment. Two experimental errors are often made when performing this experiment: (1) if the candle is lit before the bottle is placed over it, the air is initially hot, and will pull the water up the bottle as it cools, and (2) when the bottle is placed over the candle, the hot air from the candle flame expands, and some of it might escape out of the bottom opening of the bottle. Analysis of the chemistry of this experiment shows that the final products of combustion are actually more voluminous than the initial air, but other things happen to yield no net difference in the water level.

A barometer tube filled with water hangs from a spring scale as in the photograph. The water reservoir (a beaker) rests on a table, with the bottom of the tube below the water surface. A hole on the top of the tube is opened, allowing air to enter the tube, so the water in the tube flows into the reservoir. Q: After the water in the tube has been replaced by air, is the reading on the spring scale (a) greater than, (b) less than, or (c) the same as the reading with water filling the tube? A: The answer is that the scale reads less, as can be seen in the photograph at the right.

This is an interesting question for people who know that atmospheric air pressure is what keeps the water in the tube. They are then left with the problem of what exactly is the force which changes to reduce the spring scale reading after the water flows out of the barometer.