Upside down water glass trick.. IMPROVING A GREAT DEMONSTRATION

Hello I'm Bruce Shaney and today in Homemade Science we're going to look at a classic demonstration and see if we can make some improvements on it. We'll try this with some different size containers, some of them having more than one opening. Now I also want to investigate the coverings. Now this could make a great stem investigation for any age. All right to do this experiment of course we're going to need a container, but to do it well it's really going to come down to what we use for a covering. Rigid pieces like plastic work but it'll come apart very easily. Foam plates are less rigid and they'll work a little bit better. Cardboard's a good choice until it gets soggy. I like these flexible lids they work really well. This cover actually gives me a good enough seal that I can do some tricks with it. I can shake it up and down. I can wave it back and forth or around. I can even flip it in the air. There we go. I think my all-time favorite have to be these balloons. They give a really good seal. Another fun material to try is a piece of screen. It does need to be covered until you have it turned upside down. It can leak and fall apart with the slightest touch. Now going on to the containers you can start out on an extremely small scale. Of course we can always go larger and use a variety of different containers like this funnel. Put a plate on top of it. That looks pretty good. The largest container I can try it in is a five gallon bucket. Now I have adapted one by adding two sticks to the bottom. This is going to make it easier to show. The rim of the lid was cut so that it's loose fitting. Pull it up to here and I have a stopper in the bottom of it so that I can let it out. Now instead of that lid we can also just top it with this ball. Water levels right to here and I release pressure inside. So the question is why doesn't the water come out of the container when it's turned upside down? What's holding it in there? The usual answer is that it's air pressure pushing up against the bottom. Now a pressure gauge could help explain this experiment a little bit better. However this one's just not sensitive enough so I'm going to switch to this homemade one. This represents normal atmospheric pressure and if I inhale in the tube the pressure drops below that and if I exhale the pressure increases. I'll attach it to the top of this tube so we can see what's going on. Now as I start lifting the tube out of the water we can see the pressure is being reduced. We'll get it all the way out here. Reduction in pressure and if I release the cap let's see what happens. It goes back to normal. This is showing us that the pressure at the top of that container is less than that of the atmosphere. This is due to the weight of the water pushing down against that lid. Now what about if the tube's longer? Fill it up with water in this rain barrel. Attach my gauge here and as I slowly bring it up notice it's showing a greater reduction in pressure. As the water drains out the pressure returns back to normal. Now let's try it with an even longer tube. This one's 55 inches long and I'll cap it with a foam plate and there we go. That works. Back up again. As the water column gets higher the pressure at the top of the tube will continue to reduce as the increasing amount of water gets heavier. I haven't tried it yet but this one's seven and a half feet long. Let's see if we can get this one to work. All right well that didn't work. Let's try it once more. This time I'll use a balloon instead. There we go. That's better. It works. In theory we could go up to about 33 feet. At that height the pressure at the top of the tube would reduce down to zero. There is one other way that pressure can be reduced inside the container and that's when you turn it over a small amount of liquid will leak out without additional air getting inside. If I shake it really hard you can see additional water come out reducing that pressure just a little bit more. We should note that air pressure just doesn't push against the bottom. There's about 14.7 pounds of force applied against every square inch on the containers. With the atmosphere pushing against the container in all directions we can actually cap it at the bottom and also at the top. This funnel is open at both ends and it works. We can even do it with this container that's got holes on the top bottom and all four sides. There it is. I think of all these demonstrations this one's my favorite. This bottle has a string and a handle attached to it. So let's add some water and fill it up and I'll stick a balloon on top. That's pretty good and the string is going to allow me to swing it around a couple times. See if I can. There we go. Well I hope you enjoyed this video and as always I want to thank you for watching here for me so I could even flip it up in the air oops