Work and World

Do Hot Objects Fall Through Water Faster? Leidenfrost Effect!

you’ve probably never heard of the latent frost effect but you might have seen in action if you take some water and you pour it on a really hot stovetop the water will just kind of beat up and it doesn’t burn away like you think it should burn away right away right when you turn the stove on low heat the water just kind of sits there for a while and then once it gets up to heat it evaporates if you turn a stove on like say halfway as soon as you pour the water on it’ll start boiling but once you turn the stove up all the way and you can get as hot as you can get the water instead of just boiling away instantly actually floats on the surface of the metal that’s because a very thin layer of it is evaporating and it’s kind of cushioning it from the metal pan not cool just going on a circle so somebody on my Facebook page had a really good idea and you should already be friends with me on Facebook by now he had a really interesting question he said what if you heated up a steel ball and dropped it through water and here’s the two things that could happen it could fall faster through the water because just like the drop of water in the hot pan the water is never actually touching the pan so if you heated up a ball and you dropped it through the water there would be a cushioning layer of water vapor around the ball so maybe it would have reduced drag and fall straight through the water like it was not even there the other thing that could happen is the force of the water boiling against the ball will actually stop it from falling as fast and it would fall slower than it normally would fall through water and I’ve got four different size steel balls and one copper ball so we’re going to try some metals with different densities and different sizes and see if it works I also built the stand so I can reliably drop the balls from a specific height above the water so the first thing I need to do is drop all five spheres into the water and record it with a high-speed camera this is to set up a baseline and to make sure this is a valid experiment now it’s time to drop the heated spheres into the water you can probably tell I drew some inspiration from red hot nickel ball channel I picked up the hot ball and dropped it into the water I’m recording it in high-speed video so let’s view the results now now before I did this experiment I did a little bit of background research and I read a couple papers on the subject I found two papers from two different groups so the first paper I read they had a crazy increase in falling speed like 85% but the problem is they were doing it in something like acetone really low boiling point liquid in the second group did it in water but they only noticed a 10% increase in velocity not looking good remember what I said that there’s two things that can happen they can either go through the water faster or go through the water slower I was wrong there was a third thing that could happen nothing after going through the video footage I don’t think there’s any statistically significant increase or decrease in the speed that these things felt and I did it three more times and I got the same results each time well I guess that’s that guy so I will see you guys next time like and subscribe hey you should probably do what she says and press those like and subscribe buttons then don’t forget to come back here because I’m going to show you some extras right now alright we’re going to try one more thing we’re gonna put these polymer water beads into this pan and they hold like a hundred times their weight in water or something like that so they should just bounce around they’re bouncing around every we already are that’s pretty cool now let’s move on to our real experiment where this go everywhere when you heat up copper red hot in the atmosphere it forms this black layer of copper oxide now this is initially protected from contact with the water by the leading frost effect but after the ball cools and the water touches its sides it instantly boils ripping off the black copper oxide layer here’s another example of that exact moment slowed down twenty times normal speed so this is the first paper I read it doesn’t really directly relate to what I’m doing because they didn’t do it in water but they still reported an increase in velocity which means I’m at least on the right track here so this is the more interesting I guess I totally missed the most important part of this paper when I first read it and that is the graph on the top right it shows how fast a sphere will fall at different temperatures now I was heating these spheres as hot as I can get them but actually the ideal temperature is 300 degrees Celsius which I way overshot the graph is saying that a 300-degree sphere falling through water is faster than a room-temperature severe but the hotter you heat it the slower it gets so I guess both hypothesis were right after all
Video source: https://www.youtube.com/watch?v=NPJilSZyKEs

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