The experimental tool to be shown is to prove that a liquid material consists of particles. It shows very clearly that liquids consist of lots of small particles, not filling the space completely, leaving gaps in between. If we mix a glass of peas and a glass of poppy seed it does not seem very interesting, that the mixture does not fill the two glasses completely. The same result is surprising in the case of two liquids, that is water and alcohol. To show this phenomenon we can use magic flask. We must paint the two liquids to be mixed so as to see the original separation and then the mixing. Water is painted blue by metilenblue and alcohol is painted ruby by fuxin.
With the help of the funnel we fill up the lower part of the flask with water, then the upper part with methanol. The level of the alcohol should get to the half, 3/4th of the stem of the flask and this level is marked with a rubber ring. (see figure) Seal the flask with a rubber cork and mix the liquid by turning the flask 3-4 times over. The result is surprising: after mixing it the top of the liquid gets 2-3 cm below the rubber ring. (see figure) The phenomenon is known as liquid contraction. The explanation is as follows: Liquids consist of lots of small particles and when mixing them, the small particles get in the gaps between the big particles. That is why the volume of the mixture is smaller than that of the two separate liquids.
This experimental tool is suitable to examine the phenomenon of floating and sinking of objects resulting from the change of average density of the liquid. It also gives a possible physical explanation to ship catastrophies happening in the Bermuda triangle, mysterious for the public. A ship is swimming in the glass tube filled with water. (see figure) If we switch on the air pump the bubbles start from the bottom of the tube towards the surface of the water and the ship is sinking down. (see figure)
After switching off the equipment the bubbles disappear from the water and the ship appears on the surface. The explanation of the experiment is: The density of the ship is smaller than the density of the water. When starting blowing the air in, the water gets full of bubbles, so its average density gets smaller, that is why the ship sinks. After stopping the bubbles the ship comes up the surface and starts floating again.
HANGING-REVOLVING GLASS
With this experimental tool we demonstrate force originating from air pressure, but besides we can also be successful at parties with it. Fill up the glass on a tray completely with water, placed a rubber plate on the glass so as not to leave any bubbles below. After it we can show three different experiments:
The fact, that the rubber plate does not come off the top of the glass is explained by pressure originating from the pressure of the air. We can show this experiment at parties, too. The effect can be enforced by doing it with a crystal glass and filling wine instead of water.
The following motivating experimental tool makes good use when teaching torque. Fix two candles to the two ends of a stick with the help of rubber rings and placed the beam on a stand. Light first the lower and right after it the upper candle (see figure). The beam will tip over from the original position to the other side and soon back and it will go on.
The explanation is the following: After lighting them more paraffin will melt off the lower candle because its flame, due to the position of the candle, is closer to the body of the candle. So the weight of this candle will decrease faster than that of the other. We do not have to wait long, the faster decrease of the weight of the lower candle will change the direction of the torque affecting the beam and the beam will tip over to the other side. It is always the lower candle which burns faster, so the tips keep repeating and the candles see-saw until they burn down.