Glass without bottom

1997/11/01 Bandres Unanue, Luis Iturria: Elhuyar aldizkaria

• Fisika

Take a glass and fill it with water up. Next to the glass we will put some needles. With a full glass of water, would two or three needles fit without removing water? Let's do the test.

Let's start throwing and counting needles. We must tip the precautions, put the tip in the water and then leave it free to go down, without pushing, since any movement can expel water. One, two, three needles have gone to the bottom, but the water level has not changed. Ten, eleven, …, twenty, …, forty, … and the liquid is not poured. Sixty, eighty, one hundred… are found in the bottom of the needles and the water of the glass still does not pour.

It does not pour and the water level of the glass has hardly increased. Let's continue to cast needles. They are two hundred, three hundred, four hundred and a drop of water has not been poured out of the glass, but now the crust has ascended a little by the edge of the glass. This increase gives us the reason for the phenomenon. When the glass has a little fat, and normally the glasses and tableware have some ray of fat, the water soaks very little. Therefore, the water displaced by the needles, by not wetting the edge of the glass, causes the mentioned increase.

The amount of water that rises seems very small to the naked eye, but we calculate the volume of a needle and comparing it with the amount of water, we deduct that it is an infinitely smaller machine, so in a glass “full” of water fit hundreds of needles. The wider the container the more needles will be introduced, since the volume of water raised will be higher.

Let's make an approximate calculation. The length of the needles is usually 25 mm and its thickness is half a millimeter. To calculate the volume of a cylinder of this type we will use the formula .r2 h and we will see that it is 5 mm3. The volume of a needle with a head will not exceed 5.5 mm3.

Let us now calculate the volume of water ascending by the rim of the vessel. If the diameter of the container is 9 cm, the surface is 6.400 mm2. If the rise of the water layer is only one millimeter, its volume will be 6,400 mm3, that is, 1,200 times that of a needle. In other words, in the glass “full of water” more than a thousand needles fit. And so, putting the needles carefully, we can put more than a thousand needles and, at first sight, it seems that they fill the whole container… all this without the water being poured from the glass.

Currency not sunk

The coin that does not sink is not just a thing of short stories, it is something we can see in reality. And like all the events of science, experimentation will be the means to prove it. We will start by taking smaller objects than coins, such as needles. It seems that it is impossible for a loose steel needle on the surface of the water, but it is not really hard to get it.

Put on the surface the cigarette paper and on it a well dry needle. Now just remove the paper carefully. To do this, with the help of another needle, we dip the edges of the paper into the water, directing the weight towards the center; when the paper is completely wet it will sink and the needle will continue to float. Now, if we placed a magnet on the edge of the vessel, on the surface of the water, we would propel the needle by floating.

Once you get a skill clip you can leave the cigarette paper to one side and take the needle through its center dropping the water surface from a small height.

The needle can be replaced by other objects floating small and flat as a light button. After several attempts we can try with a light coin.

The flotation of these small metal parts is due to the water damaging the metal. After passing through our hands these small pieces are covered by a thin layer of fat. For this reason, a conquest is made around the needle that is floating. This conquest is not seen at first sight. Direct the liquid layers or push the needle upwards, to keep it floating.

The flotation of a needle is very simple if we first rub well with oil. In this way we can put any needle floating and will not sink.

Water in a sieve

If we were told that in a sieve water can be carried, we would probably be taking our hair. But that is possible and the knowledge of physics will help us to do so. We will take a 15 cm diameter wire sieve, without very small levels (about one millimeter) and dip the net in a paraffin bath. The wires will be covered by a layer of paraffin that is hardly seen when removing the sieve.

The sieve is still a sieve with holes between which a needle can be passed freely, but now it can be used to transport water. In this type of sieve we can have a relatively high water layer without pouring water through the holes. The sieve should be very careful and move without stirring.

Why is water not poured? As water does not wet the paraffin, very thin layers are formed at the levels of the sieve, which provoke the conquest of below, which are the ones that sustain the water. If we placed a sieve of this type on the floating water. Therefore, this sieve can be used for both water transport and navigation.

This experiment, which seems so strange, is based on a phenomenon that we use and see on a daily basis. By enlarging the containers or tanks, by greasing the plugs and chinchillas, by using oil paints, in a nutshell, by covering with oily substances all the things that we want to have out of the water, we get something that has happened in the case of the sieve that we mentioned.