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Things needed:

- 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.

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For this experiment, we use:

- 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.

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Experiment 3#: syringes with colored water.

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Experiment 3#: syringes with colored water.

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For this third experiment, we have need of:

-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.

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Things needed:

- 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.

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For this experiment we use:

-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.

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For this experiment we have to use:

-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.

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Experiment 7#: syringe with seceral holes.

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Experiment 7#: syringe with seceral holes.

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We need:

- 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.

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Hydrostatics is a branch of fluid mechanics that studies fluids. A fluids is a  substance that can flow. Liquid substances are fluids, but also aeriform substances are fluids. The difference between liquids and aeriforms is that the first one has a proper volume and the second one hasn’t a proper volume. Fluids take the shape of the container in whitch they are placed and they have density. Density is the ratio of mass and volume (m/v) and for it we use kg /m2 for unit of measurement (SI).  If temperature increase density descrease, but volume increase with temperature.

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Pressure is the magnitude F of a force acting perpendicular to a surface divided by area S of the surface over whitch the force acts.  Its ratio is P= (perpendicular)F/ S and its unit of measurement is N (newton)/ m2 = Pa (pascal). Pressure is not a vector quantity but a scalar quantity. For given pressure Force and Area must be directly proportional. For given force, pressure and area must be inversely proportional. For given Area, pressure and Force must be directly proportional.

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Then we made some experiments: milk carton and flour's experiment.

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Then we made some experiments: milk carton and flour's experiment.

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Things needed:

- 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.

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Materials needed:

- 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.

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And at the end we answered three questions:

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And at the end we answered three questions:

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Question 1:
Why snowshoes are much more effective for walking in snow?
For a given force (weight in this case) I double the area of my feet, and so the pressure will become half. This is the reason why it's easier walking with big shoes in the snow, because less pressure is produced.

Question 2:
Why does a sharp knife cut better than a dull knife?

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.

Question 3:
Why a karate chop is much more effective than a open-handed slap?

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.

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A pressure exercised  in a fluid (liquid or gas) restrained in a container, is transmitted undiminished  to all part of the fluid and the enclosing walls.

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We can explain the Pascal’s principle/law with our #7 experiment from the lesson 1 in 25/01/18. At the end of the experiment we said that the water spreads out from the holes in the same way.

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We have a hydraulic press that has two surfaces with two areas called S1 and S2 related with a incompressible fluid. We exercised a force F1  on the first surface S1, the force,for the pascal principle p=F1/S1, is transmitted unaltered in every part of the fluid. Until it reaches the second surface S2. The force exercised on this surfaces is a second force F2 because:

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

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Experiment 7# for explain pascal’s principle.

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Experiment 7# for explain pascal’s principle.

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Stevin's law, its application in everyday life and Pascal's barrel experiment.

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.

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1) In retail 3:18 of this second video Archimedes dips a "balance two arms" in water. The arm with coins is more lowered. Why?

Answer:

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.

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2) Why did Titanic sink? Search wherever you want for more informations!
Titanic sank because of Archimedes principle. With Archimedes principle you can predict if a body floats or not because he said that : "A body immersed in a fluid (partly or completely) will receive bouyancy from the bottom upwards equal to the weight of the displaced fluid ". D x V= m= g=B= W. Titanic was able to floats because its density was lower than the density of the water, but people didn’t consider weather conditions like superluna or ice melting or storms. So when the ship crashed with iceberg the water started to enter in it  and the density of the Titanic became bigger . For this reason it sank.