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163 votes

Can ants walk on liquid mercury?

Needing any excuse to break away from the work I was doing, I immediately assumed the task of answering this question. Yes, ants can walk on mercury with no trouble at all. I bet it was even kind of ...
Ian_Kinner's user avatar
150 votes

When I walk down the stairs where does my potential energy go?

Make it simple. If a mass of your weight fell down the height of three flights of stairs through the air, when it landed where would the kinetic energy accumulated by falling go? moving the earth ...
anna v's user avatar
  • 234k
94 votes
Accepted

How does light combine to make new colours?

Color perception is entirely a biological (and psychological) response. The combination of red and green light looks indistinguishable, to human eyes, from certain yellow wavelengths of light, but ...
Emilio Pisanty's user avatar
89 votes
Accepted

Does physics explain why the laws and behaviors observed in biology are as they are?

To get more insight into a question like this, you might like to ponder the relationship between logic gates and programming languages in the case of computers. This is a lot simpler than the physics—...
Andrew Steane's user avatar
87 votes
Accepted

Stood in front of microwave with the door open

The very first thing you should do is stop using your oven and have it checked out by an authorized repair service. If in fact the oven was operating with the door open, there was a failure of the ...
Bob D's user avatar
  • 72.8k
79 votes
Accepted

Could I survive at (or near) absolute zero with a very, very, very thick sweater?

A super-thick sweater probably isn't the way to go - you may be better off wrapping yourself in aluminum foil. The body loses heat through a handful of mechanisms: During conduction, your body ...
J. Murray's user avatar
  • 70k
75 votes
Accepted

Why can we distinguish different pitches in a chord but not different hues of light?

This is because of the physiological differences in the functioning of the cochlea (for hearing) and the retina (for color perception). The cochlea separates out a single channel of complex audio ...
niels nielsen's user avatar
75 votes

How can we discern so many different simultaneous sounds, when we can only hear one frequency at a time?

But that still means the ear is only moving at one frequency at any given time No, it doesn't mean that at all. It means the eardrum is moving with a waveform that is a superposition of all the ...
The Photon's user avatar
  • 27.9k
66 votes
Accepted

How do photons get into the eyes?

Yes - we are surrounded by a "sea of photons". An individual object that reflects light (let's assume a Lambertian reflector - something that reflects incident photons in all directions) sends some ...
Floris's user avatar
  • 119k
61 votes
Accepted

Can ants walk on liquid mercury?

Whether or not a small animal/insect can walk on a liquid is determined much more by surface tension than by density. To see why this is consider a dense liquid without any surface tension. You would ...
Physical Mathematics's user avatar
56 votes
Accepted

When I walk down the stairs where does my potential energy go?

The heat is predominantly generated in your muscles. More direct conversion of potential energy to heat is when a person is sliding down a pole to get to a lower floor quickly. With sufficient ...
Cleonis's user avatar
  • 21.2k
56 votes

If microwave ovens run at 2.4 GHz, what is the long-term effect on living tissue of exposure to this frequency, but with a thousand times less energy?

Bluetooth is already right in this frequency band. A typical microwave oven is 1000 W. Allowable exposure to Bluetooth energy is limited to 1.6 W/kg. So essentially this exact experiment is being run ...
Dale's user avatar
  • 102k
54 votes

Is it correct to say that "WE" feel only 5/140 of the actual weight of brain as buoyancy acts on brain due to cerebrospinal fluid?

Try not to be too pedantic with the biologists. They have our medical health to worry about. What is most likely that they are really trying to convey but failed to precisely state, is that if the ...
naturallyInconsistent's user avatar
50 votes
Accepted

How can ultrasound hurt human ears if it is above audible range?

Ultrasound is used to break kidney stones and "burn" brain tumors. So no surprise that it can damage body parts, including inner ear. The effects of ultrasound on human body are multiple. ...
nasu's user avatar
  • 8,112
49 votes
Accepted

Are human eyes interferometers?

To do interferometry in post-processing after detection of radiation, the detector must be able to record the phase of the radiation. The eye cannot do this: the photochemical reactions that record ...
John Doty's user avatar
  • 21.3k
48 votes

Is it safe to keep uranium ore in my house?

With a half-life of 4 billion years, uranium is only very weakly radioactive. In fact, since uranium is a heavy metal, its chemical toxicity is actually more of a danger than its radioactivity. If you ...
Azzinoth's user avatar
  • 2,375
45 votes

Why aren't 100% UV blocked sunglasses safe to view an eclipse with?

You are correct that almost always it is the UV content of sunlight and not its power that is the main hazard in staring at the Sun. The lighting during a total eclipse is one of those situations ...
Selene Routley's user avatar
44 votes
Accepted

Why do different letters sound different?

You don't sing a single pitch - you sing a frequency and its harmonics. Using a simple spectrum analyzer, this is me "singing" the letter A and M, alternately (AMAMA, actually): The letter "A" is ...
Floris's user avatar
  • 119k
44 votes

Why can we distinguish different pitches in a chord but not different hues of light?

Our sensory organs for light and sound work quite differently on a physiological level. The eardrum directly reacts to pressure waves while the photoreceptors on the retina are only senstive to a ...
Halbeard's user avatar
  • 754
43 votes

Why can't the human eye focus to make blurry photos/video clear?

The human eye focusing is resolving all the possible detail it can from a scene that is sharp and not distorted. The details of exactly how your brain forms an image from what your eye does is ...
StephenG - Help Ukraine's user avatar
42 votes
Accepted

How is it possible for other animals to have better night vision than humans, who can detect individual photons?

That research shows that humans can detect single photons, not that we're particularly good at it. Averaging across subjects’ responses and ratings from a total of 30,767 trials, 2,420 single-...
Cort Ammon's user avatar
  • 49.9k
41 votes
Accepted

If we feel it's hotter when humidity increases, then why do we feel it's colder when inside water?

You feel cold when heat is flowing from you to the surroundings, your body tries to burn more energy to keep up your temperature, so you shiver. Water conducts heat much more effectively than air (...
Martin Beckett's user avatar
41 votes

Why can't the human eye focus to make blurry photos/video clear?

Here's an explanation using geometric optics. I'll replace the human eye, which has a quasirandom scattering of light sensors on a curved surface, with a digital camera that has a regular grid of ...
benrg's user avatar
  • 27.3k
41 votes

If microwave ovens run at 2.4 GHz, what is the long-term effect on living tissue of exposure to this frequency, but with a thousand times less energy?

The only effect is heating. Microwaves are non-ionizing radiation which means they do not break chemical bonds. Microwaves have an energy of about 10^-5 eV. Ionizing radiation is defined by the FCC to ...
justboy4's user avatar
  • 419
40 votes
Accepted

Does pure yellow exist in variations we can't discern?

Our ability to separate different colors from each others depends crucially on how many different receptors we have for colored light. Humans have three different receptors for light, which means ...
Mikael Fremling's user avatar
39 votes

What happen if all the carbon-14 atoms in a person body decays at once?

There is about 1 radioactive $^{14}$C atom for every $10^{12}$ $^{12}$C atoms. With a half-life of 5730 years, this means there are usually about 0.2 decays per gramme of carbon per second. Carbon is ...
ProfRob's user avatar
  • 132k
38 votes

Why does blowing a whistle in someone's ear damage it more than blowing directly in their ear? Won't the whistle reduce overall energy?

The eardrum is damaged if it is stretched too far. The stretching is caused by an imbalance of pressure on either side of the eardrum. Blowing into the ear creates a stream of air that tries to enter ...
Mark H's user avatar
  • 24.1k
38 votes
Accepted

Can human ear hear 4 Hz frequency, if I tap my hand 4 times per second on table?

You are not producing a 4 Hz wave—you are producing four sets of sounds, each with a spread of audible frequencies. If you had a 4 Hz sinusoidal wave you would not hear it. If you tap a drum, for ...
Marco Ocram's user avatar
  • 26.3k
37 votes

Does physics explain why the laws and behaviors observed in biology are as they are?

Emergence Physics does not determine every facet of biology! Biology is a great example of what is called emergence - the phenomena where the composite of many simple entities has properties that the ...
Roger V.'s user avatar
  • 59.4k

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