Lesson 14 - Pascal's Principle - The Properties of Liquids - Demonstrations in Physics

how do you do ladies and gentlemen and boys and girls I am Julia Sumner Miller and physics is my business and our very special business today is the work of the young Frenchman Blaise Pascal a genius of the 17th century who died at an early age indeed at 39 but left enough for us to contemplate for lifetime and I urge you to read his life written by his sister the Lavi Blaise Pascal the life of Blaise Pascal indeed at the age of 12 he happened one day to strike a dinner plate belonging to his mother and it rang out and he was less led to write a definitive paper on vibrating bodies I urge you to go read about him now one of the principal things he had concern with was the property of liquids in the fluids and raised a very interesting problem considered oh let us get a picture of him here he is just some few years before his death Blaise Pascal a genius of the 17th century consider the following supposing I have a vessel shaped like that another one with the same base shaped like that and another one with the same base shaped like that three identical vessels that is the basis identical and now I fill them with water to the very same level water water water question on the bottom of which vessel do we have the greatest force Enza discussion most water here most massive water most weight of water the bottom here supports all the water bounded by those vertical lines the bottom here supports the water bounded by those vertical lines the bottom here supports the water bounded by those vertical lines well so somebody says somebody I see water in here and water in here what holds that water up answer the sides then somebody says there's no water in here and no water in here and yet the push on the bottom is the same and say yes reason the walls push in with a force which compensates for the water which is not there and I'm going to show you this with a wonderful experiment here it is here it is here is a narrow walled vessel and I'm going to fill it to a certain level by raising a chamber of water here comes the water here comes the water there comes the water go up hold it right there I'll get the water level in here proper as measured by the position of this marker and if we read the scale it reads about forty three or four no I'm going to let the water run out of there and replace this vessel by a very big one quite like the middle vessel that I drew on the board and I hope you see that this vessel is vastly bigger than this one but they have the same basis they have the same base I'm going to screw that on there if I can do it here there we go and now I'm going to raise the water in here to the same level as in the other one and I hope you will see that the gauges read the same they're always a little trouble with the linkage system in such a mechanism so there may be a little trouble but I'm bringing the water up to the same level since the sides are flared out the rate of growth of depth is less but there we have it oh I've exceeded the level a little bit I'll come down a little I'll come down a little and I think that's evidence enough that the readings are identical the readings are identical amazing piece of business consider another consequence of Pascal's work supposing I have a little chamber here connected to a big chamber here and I put a piston in this chamber and a piston in this chamber and this is filled of course with some incompressible fluid oil of water you are aware that if I push down on this piston the water goes up there and lifts that piston this is an hydraulic press if indeed I make this a compound machine by attaching a lever in this manner and I apply a force here I can pump the liquid from here down and lift an enormous load indeed if this piston is very small compared with that one I can multiply the force I apply here depending upon the length of this lever thousands of fold and I'm going to show you that here I have such a system here I have such a system a little piston right here and a big piston right there and here is a block of wood here is a block of wood and I say it takes about a ton of force to break that wood and I can't do it with the unaided hand but let me put it in there oh oh I made a little mistake I have to come down a bit watch it now watch I am going to deliver and here is what I wish you all to see that with ever so tiny a force applied out here with my little finger I can produce a force of about one ton at the middle of the board above this piston watch it now watch the scale oh well this board broke at about half a time now you know very well that I could not exert a force of half a ton with my naked hands here is a board a piece of two by two I would say that it will take about two times to break this about two tons now watch it this is fantastic applying Pascal's view that the liquid is incompressible and any small force applied here is felt without loss in all parts of the machine watch it now there it reads a ton and a half there it fractured it something around a ton and a half and I say that is fantastic Oh staggering staggering the forces we can impress here now I could show you another experiment with that hydraulic press here is a spring I will not pursue the adventure but this spring has an enormous modulus meaning that it takes extraordinary forces to squeeze it together more than two tonnes in fact I couldn't do it with the naked hand but there I could do it very easily let us consider another consequence of Pascal here's one of very great usefulness to the human race here is a hypodermic needle question why is the needle sharp very pointed Enza for the same reason that you wear snowshoes to cross deep snow you spread your force out over a large area so the pressure the pressure which is the force per unit area is very high here in the needle for example ladies with high heels a little girl weighing a hundred pounds can leave more impression on a an earth Road than an elephant imagine that why because her weight is on so small an area so here we have it I push with a force of ten pounds with my thumb the hypodermic needle has a pointed area of about a thousandth of a square inch the pressure is 10,000 pounds per square inch fantastic fantastic consider another one this is beautiful here I have a flask filled with colored water one-hole stopper in a glass tube and I call your attention to the level of the water right here I hope you can see it the level of the water right there a little difficult there that's very good beautiful no what am I going to do I'm going to squeeze on the wide sides of the glass and we see an astonishing thing watch the level of the water watch it there it goes up suggesting two things that the glass is very elastic and the water highly in compressible another adventure with the same thing let me turn the glass sideways let me squeeze on the narrow sides question what will the level of the liquid do answer when I squeeze the wide sides I deform them inward diminish the volume of the vessel and up when the liquid when I squeeze them on the wide sides will I not bulge out the wide walls and will not the liquid fall watch it there it is it goes down another adventure which you can pursue the Cartesian diver here I have a little creature in the shape of a man in which we have put some water any floats at a certain position there is some air above the column of water there is some air in him what am I going to do I'm going to push down on that rubber sheet here that force by Pascal is communicated without loss to all parts the water in him filled in here feels it the water in him feels it the air inside of him feels it and because the air is compressible it gets compressed more water goes in and he goes down so you see it is not me pushing that pushes him down is this sequence of actions watch it there it is I love that little business and what I can stop him where I want since they are differently loaded they ride at different positions now you can make one very easily you don't need such a thing as that a little medicine vial would do such as little pills and the light come in and here it is here it is there is like a submarine in fact exactly how a submarine works I release the force or the pressure and up he comes consider another consequence let's go over here back to this table because there are some enchanting things here is an experiment which we could do but we will not we will consider it a virtual demonstration here is a flask filled completely with water completely with a tight-fitting stop liquids I say are incompressible conclusion I can deliver a sharp impulsive blow to that stop up so that force would be felt in all parts of this chamber and it would burst into a million bits and the water and glass scatter enormous why because Pascal said any force delivered to a liquid is communicated without devolution without any lessening to all parts another one of the same kind here is a wooden block with some nails in it and here is a flask unfortunately this flask has a bubble in it which I think you can see and bubbles of air are highly compressible I cannot therefore do what I want to do but supposing I fill the flask completely full of water I could then use it with absolute impunity to drive that nail into that block why because water is highly incompressible and the water the vessel would feel nothing this would act like a solid hammer another consequence of Pascal end of Torah chili beautiful thing I have a can here filled with water and I hope you can see on a close shot that there is a hole in that can and yet the water does not come out and I say that's fantastic I'm going to pull out the stopper watch it I'll give you evidence that there's water there there it is I put the stopper back in the water has ceased running out question what's holding it in obviously atmospheric pressure question question very important how taller can could I use to do this answer 34 feet isn't that fantastic fantastic now one more demonstration one more I have here a YouTube a YouTube that's a tube shaped in the form of you mercury in the bottom part water colored above it and you see there is a difference in levels in the mercury columns what will be the ratio of the water level to the difference in the mercury levels answer thirteen point six which is the specific gravity of mercury and I invite you to do this experiment and wish you good fortune you

Channel: Professor Julius Sumner Miller

Views: 806,534

Rating: 4.9127111 out of 5

Keywords: science, julius, sumner, miller, dramatic, demonstrations, physics, professor, Demonstrations In Physics (TV Program)

Id: 8ma4kW3xVT0

Length: 14min 52sec (892 seconds)

Published: Mon Feb 03 2014

Reddit Comments

[u/mushbo]

I used to watch this guy on TV. Interesting.

[u/theXarf]

He has a very shiny face.

[u/xixspiderxix]

Let me just find a pound of mercury to do this experiment real quick....checks out

[u/palordrolap]

He has a look of Patrick Troughton (best known as the 2nd incarnation of Doctor Who) about him.