Hot answers tagged

110

The premise of this question is wrong. If the moon is in between the earth and the sun (as shown on your diagram), and you can see the moon, then it is day, not night: If on the other hand, you are on the opposite side of the earth during that configuration (so that it is night), then you can't see the moon because the earth is blocking your view of it:


50

The sun doesn't just illuminate the moon directly. The moon is also illuminated by sunlight reflected from the earth. This is called earthshine. This makes the parts of the moon that face us visible even when the sun is on the other side. According to NASA, it was Leonardo da Vinci who first explained this. As an example, the brightly lit portion of ...


27

I'm really winging this one because the last time I did an equilibrium calculation was 35 years ago! But I'm fairly sure of a partial answer (see discussion at end). A gas's solubility in water (or liquid generally) almost always decreases with increasing temperature. This phenomenon is explained in a way very like the explanation of the increase in ...


23

While excellent answers have already been provided (yes, it's Earthshine; yes, when the Moon is between the Sun and the Earth, you don't see the Moon at night, you see it from the daylit side of the Earth) given all the "artist's renderings" in the question and the answers, I thought it might be useful to include a diagram that demonstrates the actual scale ...


16

If it is really between the earth and the sun it is called a "solar eclipse" and and the moon's shadow falls on the earth at certain places, because it is not large enough to cover the whole sun except on a shadow path. A total solar eclipse occurs when the Moon completely covers the Sun's disk, as seen in this 1999 solar eclipse. Solar prominences can ...


12

The diagram you drew is flat, but the solar system is not. The Moon's orbit is not in the same plane as the Earth's orbit. Wikipedia has a nice diagram: Because of this, when the Moon is "in between" the Earth and the Sun, it is usually a little "above" or "below" the Sun as well. You can observe this for yourself: one or two days after the new moon, ...


11

The claim that frictional force does not depend on area of contact is not, in general, true. It is a good enough approximation for many cases that it can be used for many real world calculation and even more back-of-the-envelope estimates, but it fails under several circumstances. Conditions for failure of the not-area-dependent approximation include (but ...


11

This answer was meant as a comment to @WetSavannahanimal aka Rad Vance but it is rather long and I hit the character limit. The reason for the opaque center should be due to the manner in which the water volume is freezing. Presumably the solution is not mixed and the outside freezes first forming a crystalline (ice) wall through which the gas cannot escape....


8

A human can produce about 100 W power continuously. That is equivalent to a couple of lightbulbs. So, while pedalling continuously you can keep one room reasonably lit. In one hour, that means you can generate a total energy of 0.1 kWh. A top athlete will be able to do better, so let's say it is possible to generate 0.2 kWh in 1 hour. That is still nowhere ...


8

The short answer: Cloudy ice is caused by gases (mainly nitrogen and oxygen) dissolved in the water that come out of solution when the water freezes. The small bubbles trapped in the ice cause the white appearance. Boiling the water removes the air dissolved in it, producing clear ice as a result. Assuming that other impurities don't produce the same cloudy ...


4

For plastic water bottles of the market, Msha gave a video link ,in a deleted, unfortunately, answer because it just gave the link.For this case, plastic bottles, it should be the answer chosen. Crush the bottle fast, beginning from the bottom. The same will be true for any elastic type bottle. It is only glass bottles that have an unsqueezable limit. I ...


3

Water boils at $100 ^\circ~\mathrm C$. $30$-$45^\circ~ \mathrm{C}$ is not nearly enough to boil water, but the constant heat of the sun is enough to evaporate water over time. It takes about $4.314~\mathrm{J/K}$ to evaporate 1 kg of water (under normal atmospheric pressure). The can slowly evaporate the water on the ground, but $30$-$45 ^\circ~\mathrm{C}$ is ...


3

The probable reason why poeple say ice cream heats up your body is when you compare the amount of heat that it takes away your body compared to the food caloric value of the ice-cream. 100 grams vanilla ice cream is about 207 food Calories ($207 kcal$) according to this site. On the other hand, the amount of heat that the ice cream takes from the body is ...


3

It is unrelated to physics, but is part of a brand called psychophysics, that is, the study of perception. In the visual psychophysics branch of depth perception, you are interested in finding not only what depth information reaches your eye, but how and if all this information is used by your brain to estimate depth. Not all optic information is there to ...


2

One thing everyone seems to have forgotten is the "tar" in tarmac. There is more than just friction on a race track there is also adhesion. drag strips will typically have fresh tar at the beginning and be very tacky. think of it like the tires being glued to the track both by the tar and the melted "rubber" material of the tires. the more surface area for ...


2

Hold the bottle upside down, your hand grasping it near the base. Extend your arm downwards. Make a circular, conical-shaped motion with your hand. Keep it up until you have a nice vortex going. Spinning too fast is counter productive; centrifugal force keeps too much water hugging the sides. You need a speed just a bit more than what's necessary to ...


1

The moon circles around the earth, so half the time it is between the earth and the sun and half the time the earth is between the sun and the moon. Therefore also the moon rises and sets, the same way the sun rises and sets. If it's midnight (your are on the opposite site of the earth than the sun) and the moon is betweem the sun and the earth you can't ...


1

I think this happens because when windows are open then there is free airflow in the room and doesn't affect the shutting of the door but when the windows are closed then there is obstruction in airflow. The pressure of air inside the room become less than the pressure of air outside the room and hence obstruct the shutting of the door in the room having all ...



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