- plasticine 

- a becker 

- water 

How to proceed: 

Fill the becker with some water. Then, model 2 pieces of plasticine. The first one has to being shaped like a little ball. The second one, has to look like a bowl (you can give it that shape modeling a sphere and then pushing in the middle of it). Put the ball of plasticine in the becker: you'll notice that that ball will sink, and that the level of water will rise. After that, put the second piece of plasticine in the becker. This one will float, and the level of water won't change. 

- 2 "empty" syringes (there is air inside)

 -a plastic tube.

We connect the 2 syringes with the plastic tube and we push the piston of one of the two: we notice that the other syringe rises up.

-2 syringes

-artificial food colouring

- becher

- water

- plastic tube

- pipette

First of all, we fill the becher with some water and some artificial food colouring, then we mix with the pipette.

We put the artifical food colouring into the syringes and then, thanks to the plastic tube, we connect the 2 syringes.

We notice one thing: the level of water change when the 2 syringes are in two different heights, while the level stays the same when we put them at the same height.

- a little toy fish with a hole 

- a plastic bottle 

- water 

How to proceed: 

Fill the bottle with water, and then put the toy fish in it. Then, close the bottle with its cork. Wait some seconds, and you'll see the fish sink. Add pressure in the bottle with both your hands: the fish will move, depending on where you pushed. If you push at the bottom, the fish will arise; if you push at the top, it will go down.

-scotch 

-water

-a bottle with two holes. The first hole is in the half of the bottle and the second is under and parallel to the first one. 

We have to cover two holes with a piece of scotch and put the water in the bottle. The experiment starts now because we have to take off  the piece of scotch and let the water comes out. 

In this moment we can notice that the first hole’s water spray is lower than the water spray of the second hole. 

-water

-scotch

-a bottle with one hole (that is in the half of the bottle). 

-the bottle’s cork

First of all we have to cover the hole with a piece of scotch and put the water in the bottle like in experiment number 5. Then we have to close the bottle with its cork and we have to take off the  piece of scotch. Now we can see that the water doesn’t come out the hole, but if we take off the cork the water begins come out the hole. 

- a big syringe with many holes 

- water

Make holes all around the top of the syringe and then, close them with a piece of scotch. Put the water on the syringe and remove the scotch. Push the piston of the syringes. We notice that the water spreads out from the holes in the same way.

- 1 carton of milk (empty and closed) 

- some flour 

How to proceed: 

Make a heap of flour, ensuring that the top of the surface is flattened. Then put the carton on it, laying it on its three dimensions: on its length, on its width and on its base. You'll notice that the sign left by the carton in the flour will change. 

That's because of the different pressure which acts on the dimension of the carton when it lays on the flour. When the carton lays on its base, the sign left by it in the flour will be deeper, because the pressure is concentrated on a smaller surface (the one of the base). If instead the carton lays on its length, the surface will act on a bigger surface and so the sign left in the flour will be less deep. 

- 1 balloon

- 15 push pins 

How to proceed: 

First, blow up the balloon and tie it; then place 15 push pins closely together with the tip upwards. Put the balloon on the top of the group of pins, put your hand on the balloon and push down.

Now, put 1 pin point side up on the table and take the balloon. Put it on the pin and push down with your hand. 

We can think about surface tension like skin. If you had one pin pushing into the balloon the pressure would cause the explosion of the balloon. In the first case, the pressure is distributed to 15 points allowing surface tension to distributed the pressure, so the balloon doesn't explode.

For a given force, if the surface of the knife is smaller, the pressure applied will increase and so this makes the knife cut better. In fact, pressure is the one which acts directly on the surface. 

For a given force extended in a smaller surface, a bigger pressure will be produced: that's why a karate chop is more effective than a OPEN-HANDED slap.

F2=p S2= (F1/S1) S2= F1x (S2/S1).

Date: 03/02/18.

In the previous lesson we talked about the Stevin's law, its application in everyday life and the true story of Pascal's barrel experiment.

Stevin's law:

The pressure at a point in a liquid in static equilibrium depends only on the depth at that point.

The formula is: 

P = P0 + d×g×h, where:

P0 is the external pressure on the surface of the liquid.

D is the liquid density

G is the gravity acceleration

H is the depth.

We can do an example to explain in a better way this law: the communicant vassels.

There are several connected vassels with different shape and volume: if we put a homogeneous liquid, when this settles, it balances out to the same level in all the containers.

Then, during the previous lesson, we talked about the Pascal's barrel experiment, where the mathematician did a bet with a friend, saying that he would have broken a barrel fille of water, whose pressure is slightly lower than the limit of tolerance of the barrel itself. If a thin tube is placed above the cask and it is progressively filled with water, once the limit had been reached, the pressure of the fluid causes the break of the barrel.

The experiment consists in the fact that, despite the addition of quantities of water with an ever-increasing weight, the limit share of the fluid corresponding to the breaking of the cask is always the same.

In water, the arm of the balance with golden coins is more lowered than the one with the golden and silver crown, because of the different density between the crown and the coins. In fact, gold is denser than silver; as density it's inversely proportional to volume, gold will have less volume than silver.