Simple Demonstrations With Air (1962)

[Music] [Applause] do you think this glass is empty actually it's full full of air air is all around us we can't see air but by performing some simple demonstrations we can see many of the things it does we can see that this glass is full of air when I push it underwater the air in the glass takes up space and prevents the water from entering so air occupies space let's demonstrate this again this glass has a hole in it I'll cover the hole with my finger to keep the air in the glass water cannot enter Because air is occupying the space when I allow the air to escape the water comes in and takes its place we know the air in this ball is taking up space this weight just balances the ball suppose I put more air into the ball will it be lighter or heavier with more air in it with this air pump I'll put more air into the ball now let's wait weigh it it is heavier with more air in it so air has weight let's demonstrate this in another way this can contains air when I place it in water it barely floats now since air has weight what will happen to the can if I add air from this hose will it be heavier yes the can sinks adding more air added enough weight to the can to cause it to sink this can is full of air but I'm going to dry some of it out I'll put some water in the can and this hot plate will boil the water changing it to steam the water is boiling now and the steam is filling the can driving the air up out carefully to avoid getting burned I'll take the can off the hot plate and put the cap on as the steam inside the can cools it condenses back into water taking up less space now there is less air inside the can than there was before watch what the air pushing against the outside of the can is doing the can is being crushed by the air pressing on it we say air pressure is crushing the Can Air exerts pressure we had very little air pressure inside the can the air pressure around it was much greater great enough to crush the can what would happen if the air pressure around the container were much less than the pressure inside it we can find out with these two glass cubes they're filled with air and sealed so the air cannot escape this pump called a vacuum pump can remove much of the air from this jar AS the air is removed from the jar the pressure around the cubes is becoming less and less but the pressure inside the cubes Remains the Same pushing out on them now watch closely as the air pressure around the cubes becomes much less than the air pressure inside the cubes we've seen two effects of changing air pressure this balloon will help us see what happens as the air pressure changes in the jar I'll pump the air out of the jar AS the air is removed from the jar pressure around the balloon becomes less and the greater pressure inside the balloon causes it to expand now I'll let air back into the jar as the air pressure increases it pushes in on the balloon making it smaller the balloon does not change in size when the pressure inside and outside the balloon is the same that's why our bodies are not crushed by air pressure there is pressure inside our bodies that is the same as the air pressure outside our bodies How great is the air pressure around us here's one way we can measure air pressure this glass tube is sealed at one end I'll fill the tube with mercury a liquid metal now the tube is completely filled with Mercury and there is no air left in it I'll place the open end in this bowl of mercury to measure the column of mercury I'll attach it to this yard stick now do you know what I've made it's a simple barometer here's how it works we know the space at the top of the tube contains no air because the tube was filled with Mercury so there is no air pressing down on the top of the Mercury column but at the bottom of the barometer there is air pressing down on the mercury in the bowl this air pressure holds the Mercury up in the tube by measuring the height of the column of mercury we can measure the air pressure at sea level normal air pressure will hold up a about 30 in of mercury now let's see what will happen if we change the air pressure on the Mercury to change the air pressure we'll use a barometer sealed in this tall jar the jar is connected to the vacuum pump in such a way that I can pump air into the jar as well as out of it changing the air pressure on the Mercury of course this will change the pressure more than it would ever change in our atmosphere when I use the pump to remove air from the jar the pressure supporting the Mercury column becomes less the column of mercury gets lower now I'll pump air into the jar AS the pressure increases the column of mercury gets higher by measuring the height of the Mercury column we can measure the change in air pressure scientists know that when the air pressure around us changes the weather usually changes so measuring the height of the Mercury column helps us in predicting the weather many newspapers tell what the barometer reading is every day so air is all around us and even though we can't see it we can see the things it does let's remember what we've seen air occupies space air has weight and air exerts pressure these are three important facts we need to know as we learn more about air and air pressure