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1500 questions
90
votes
2 answers
Why is a laserpointer able to "erase" a glow-in-the-dark sticker?
a while ago I tried to charge a glow-in-the-dark sticker using a simple red laser pointer. It was a large sticker, of the type used to mark emergency exits and fire extinguishers here in Germany. I thought I could draw a picture this way, with…
Toastor
- 781
90
votes
7 answers
Why do metals only glow red, yellow and white and not through the full range of the spectrum?
Why don't metals glow from red to yellow to green to blue etc.? Why only red, then yellow and then white? Shouldn't all wavelengths be emitted one by one as the temperature of the metal increases?
If some metals do glow at with different colours,…
Dieblitzen
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90
votes
14 answers
Superluminal neutrinos
I was quite surprised to read this all over the news today:
Elusive, nearly massive subatomic particles called neutrinos appear to travel just faster than light, a team of physicists in Europe reports. If so, the observation would wreck Einstein's…
Sklivvz
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89
votes
9 answers
When I walk down the stairs where does my potential energy go?
When I leave my room I walk down three flights of stairs releasing about 7kJ of potential energy. Where does it go? Is it all getting dispersed into heat and sound? Is that heat being generated at the point of impact between my feet and the ground,…
A. Kriegman
- 1,246
89
votes
3 answers
How does this baby rattle work?
Here's a gif showing how the balls move when I move the rattle. The circular tube hangs vertically, with the balls on the bottom. There are more images in the bottom.
The balls roll freely inside the tube
The inner diameter of the tube is larger…
Stewie Griffin
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89
votes
6 answers
Why is light bent but not accelerated?
Light is bent near a mass (for example when passing close to the sun as demonstrated in the famous sun eclipse of 1919). I interpret this as an effect of gravity on the light.
However, it seems (to me, at least) that light is not accelerated when it…
René Nyffenegger
- 1,133
89
votes
5 answers
Why does a full moon seem uniformly bright from earth, shouldn't it be dimmer at the "border"?
I know the moon is not uniformly grey, it has details, craters, it's not just a colored uniform circle from earth, however, when in a full moon, the intensity of the light received from different parts of the "disc" seems very similar.
Let's define…
Santropedro
- 1,426
88
votes
9 answers
Why doesn't the Moon fall onto the Earth?
Why doesn't the Moon fall onto the Earth? For that matter, why doesn't anything rotating a larger body ever fall onto the larger body?
Adir Peretz
- 1,023
88
votes
10 answers
How can magnets be used to pick up pieces of metal when the force from a magnetic field does no work?
I learned that the force from a magnetic field does no work. However I was wondering how magnets can be used to pick up pieces of metal like small paperclips and stuff. I also was wondering how magnets can stick to pieces of metal like a…
sTr8_Struggin
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88
votes
6 answers
How exactly do you avoid fooling yourself?
In cargo cult science Feynman writes:
"Millikan measured the
charge on an electron by an experiment with falling oil drops, and
got an answer which we now know not to be quite right. It's a
little bit off, because he had the incorrect value…
Trevor Andrade
- 841
88
votes
3 answers
Why do phones land face down?
Layman here.
I'm not sure if this is the case or not, but my anecdotal evidence is that mobile phones, especially large screen phones, tend to fall face down when you drop them; much to the owner's dismay, this leads to cracked screens.
I'm sure…
Möoz
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88
votes
4 answers
Why does rainwater form moving waves on the ground? Is there a name for this effect?
A while ago it was raining and I noticed that, on sloped pavement, water was flowing in very regular consistent periodic waves, as you see below.
However, I realized I had no idea why this should be happening. There was nothing uphill actually…
user541686
- 4,131
88
votes
4 answers
Why is a $5-60 mph$ time slower than a $0-60 mph$ time for some automobiles?
This doesn't make a lot of sense to me, from a physics 101 point of view. I've read a few blog entries on why this is, but none of them explain it well or are convincing. "something-something launch control. something-something computers." …
marathon
- 773
88
votes
11 answers
Why must a physical theory be mathematically self-consistent?
I always read in modern physics textbooks and articles about the need for physical theories to be mathematically self-consistent, which implies that the theories must not produce contradictions or anomalies. For example, string theorists are proud…
Maxis Jaisi
- 1,281
88
votes
5 answers
How do laser "tape measures" work?
There is a device available for about $\$40$, which fits in the palm of the hand, runs on two AA batteries, and can measure distances up to $50\,{\rm ft}$ to an accuracy of $\sim \frac{1}{8}''$ ($\sim 3\,{\rm mm}$).
Light travels $300,000\,{\rm…
Anthony X
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