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Course: LeBron asks > Unit 1
Lesson 1: LeBron asks- LeBron Asks: What muscles do we use when shooting a basket?
- LeBron Asks: How does shooting a basketball illustrate Newton's 3rd Law?
- LeBron Asks: If Earth's history were a basketball game, when did humans appear?
- LeBron Asks: Why does sweating cool you down?
- LeBron Asks: Why does humidity make it feel hotter?
- Free-throw probability
- Three-pointer vs free-throw probability
- Monte Carlo simulation to answer LeBron's question
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LeBron Asks: Why does humidity make it feel hotter?
LeBron asks Sal why humidity makes it feel so much hotter. Created by LeBron James and Sal Khan.
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How does a dehumidifier actually remove the humidity from the air in your house?(129 votes)
Imagine enjoying a soda during a particularly warm day. When you pick up the can, you might notice that it's wet -- there's moisture on the outside. Why is that? As air loses heat, it also begins to lose its ability to retain moisture; the colder surface pulls and collects water from the warmer air, creating condensation. Your dehumidifier does pretty much the same thing. Most dehumidifiers can be broken down into five component parts:
•Fan Compressor -- This compresses and expands a refrigerant gas like freon to cool the dehumidifier's coils. (See How Air Conditioners Work for a more detailed explanation of this cycle.)
•Reheater -- This captures and collects heat that the cooling process generates.
•Compressor cooling coils
•Reservoir
How do all these parts fit together to pull moisture from the air? It's fairly simple, but very effective:
1.A fan collects air from the surrounding area and pulls it into the dehumidifier.
2.As the air passes through, it comes into contact with the dehumidifier's cooled coils. These coils use condensation to pull moisture from the air. The collected moisture remains on the coils and drips into the dehumidifier's reservoir.
3.The dehumidifier reheats the air and exhausts it back into the room.
A dehumidifier usually has a removable plastic bucket for a reservoir; most buckets also have a place where you can hook up a hose so the collected water can drain straight into a floor drain or pump. This frees you from having to remember to dump out the water. But don't worry too much about the reservoir overflowing -- most dehumidifiers also have an automatic shut-off. If you're using a dehumidifier in extremely moist conditions, however, or if you need to keep your dehumidifier on all the time, you should look into a unit with a built-in condensate pump, which regularly pumps water out of the unit's reservoir rather than simply relying on gravity to empty it as a hose does.
Many dehumidifiers also have a humidistat, which allows you to set your desired level of relative humidity. A humidistat has two parts: a sensing element and a relay amplifier. The sensing element includes two alternate metal conductors, and changes in relative humidity will cause electrical resistance between those conductors. The relay amplifier measures this resistance and sends a signal to turn the dehumidifier on or off. These basic components add up to a device that may make your home feel a whole lot better.(190 votes)
at what point would it start to rain, 100%? could it be 70% humidity and raining? also, would rain cool you down or heat you up?(47 votes)
Great question! The answer is yes... you can observe a lower humidity on the ground than 100% while it's raining. It turns out that humidity can change a lot as you move from the ground up through the atmosphere. If it's raining, it simply means that the humidity "somewhere" above the ground is 100%. Bear in mind, a lot of other things have to happen besides reaching 100% humidity somewhere in the atmosphere to create rain. But, once a rain drop forms and is heavy enough to fall to the ground, it can fall through levels of the atmosphere with humidity lower than 100%. Those rain drops can start evaporating and shrinking as they pass through these drier layers, and sometimes they can even evaporate completely. This is called virga. But, if they're big enough they'll fall completely through these layers all the way to the ground. So yes, you can measure humidity near the ground of less than 100% while it's raining!(55 votes)
If fog is 100% humidity would you not be able to breathe in fog? We can obviously breathe in fog (I've done it, haven't died :P) but if it's one hundred percent humid then wouldn't it be the same as breathing in pure water?(25 votes)
Air is saturated before it holds enough water to become liquid.(1 vote)
- so a cloud is 100% humidity what about fog???(15 votes)
So is fog. It is just a cloud at ground level.(44 votes)
- When the weather person gives the weather report and mentions humidity, they also sometimes mention dew point. What is dew point and is it related to humidity?(10 votes)
- The dew point is the temperature below which the water vapor in a volume of humid air at a constant barometric pressure will condense into liquid water. Condensed water is called dew when it forms on a solid surface.(13 votes)
- why do some people use humidifier when they are sick?(7 votes)
Because humidity, which is what the humidifier produces, clears out your sinuses and helps you breathe through your nose. So its good to live in a place that is naturally humid. Helps when your sick(6 votes)
How do they actuallly measure the hunmidity(5 votes)- There are various devices used to measure and regulate humidity. A device used to measure humidity is called a psychrometer or hygrometer. A humidistat is a humidity-triggered switch, often used to control a dehumidifier.
Humidity is also measured on a global scale using remotely placed satellites. These satellites are able to detect the concentration of water in the troposphere at altitudes between 4 and 12 kilometers. Satellites that can measure water vapor have sensors that are sensitive to infrared radiation. Water vapor specifically absorbs and re-radiates radiation in this spectral band. Satellite water vapor imagery plays an important role in monitoring climate conditions (like the formation of thunderstorms) and in the development of future weather forecasts.(3 votes)
- Wait. So when it is 50% humidity, there is an equal probability that your sweat will evaporate and that water will condense on your arm?(5 votes)
when water evaporates does it cause humidity(2 votes)- If you had a bucket of water poured on you and you were in a closed room with 100% humidity, would you be able to dry off?(3 votes)
There is always some water evaporating. You would drip-dry extremely slow though, but I still think that you would dry.(1 vote)
Video transcript
LEBRON: Some reason Miami can be hot. I'm told the humidity makes it hotter Why is this? KHAN: Excellent question LeBron. Let's first think about what people are talking about when they even say "humidity" And there's a couple of ways to think about humidity, but typically when you are the weatherman or in everyday talk people say "Hey it's really humid out there." or "It's high humidity." They're talking about relative humidity, and it's usually indicated by a percentage Let's just think about what the different percentages of relative humidity mean. So right over here, we have 0%. So right over here, we have 0% relative humidity. and over at the extreme other hand, you have 100% relative humidity. at any given point, the air is some place between 0% humidity and 100% relative humidity. at 0% relative humidity is essentially saying that there is no water vapor in the air or non-measurable amount of water vapor in the air. As we go to this molecular view of what it might look like little water droplet maybe on our surface of our skin So just to be clear, these are the skin molecules - not even skin cells, which will be the actual skin molecules. Let's just simplified them as brown circles. And this right over here - this is the actual water molecules. So these are water molecules And maybe is a drop of sweat, or little water that got dropped on our skin and it is in liquid state you have this hydrogen bond between the molecules that are super strong so allows these molecules to slide pass each other and that's why liquid flows the way it does. And we've already talked about why sweat makes you cooler but warm up you a little bit. Captions by Isaac@RwmOne (youtube.com/RwmOne)