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1500 questions
151
votes
2 answers
Why does a mirror split my laser beam?
Last night my daughter was asking why a mirror "always does that" (referring to reflecting a spot of light). To help her figure it out, I grabbed my green laser pointer so she could see the light traveling from the source and reflecting off the…
Wayne Werner
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150
votes
13 answers
Is time continuous or discrete?
I was coding a physics simulation, and noticed that I was using discrete time. That is, there was an update mechanism advancing the simulation for a fixed amount of time repeatedly, emulating a changing system.
I though that was interesting, and now…
jcora
- 2,109
149
votes
10 answers
Why is my hand not burned by the air in an oven at 200 °C?
I have this problem from University Physics with Modern Physics (13th Edition):
The inside of an oven is at a temperature of 200 °C (392 °F). You can put your hand in the oven without injury as long as you don't touch anything. But since the air…
InfZero
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148
votes
2 answers
Does the Planck scale imply that spacetime is discrete?
On a quantum scale the smallest unit is the Planck scale, which is a discrete measure.
There several question that come to mind:
Does that mean that particles can only live in a discrete grid-like structure, i.e. have to "magically" jump from one…
vonjd
- 3,701
146
votes
8 answers
Why does a remote car key work when held to your head/body?
I was trying to unlock my car with a keyfob, but I was out of range. A friend of mine said that I have to hold the transmitter next to my head. It worked, so I tried the following later that day:
Walked away from the car until I was out of…
SjonTeflon
- 2,229
144
votes
7 answers
Calculus of variations -- how does it make sense to vary the position and the velocity independently?
In the calculus of variations, particularly Lagrangian mechanics, people often say we vary the position and the velocity independently. But velocity is the derivative of position, so how can you treat them as independent variables?
grizzly adam
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144
votes
3 answers
Why are the windows of bridges of ships always inclined?
What is the reason that the windows of ships' bridges are always inclined as shown in the above picture?
veronika
- 2,706
143
votes
7 answers
Why doesn't water boil in the oven?
I put a pot of water in the oven at $\mathrm{500^\circ F}$ ($\mathrm{260^\circ C}$ , $\mathrm{533 K}$). Over time most of the water evaporated away but it never boiled. Why doesn't it boil?
Hovercouch
- 1,421
143
votes
6 answers
If you view the Earth from far enough away can you observe its past?
From my understanding of light, you are always looking into the past based on how much time it takes the light to reach you from what you are observing.
For example when you see a star burn out, if the star was 5 light years away then the star…
JD Isaacks
- 1,853
142
votes
24 answers
How do I experimentally measure the surface area of a rock?
I hope this is the right place to ask this question.
Suppose I found a small irregular shaped rock, and I wish to find the surface area of the rock experimentally. Unlike for volume, where I can simply use Archimedes principle, I cannot think of a…
Pritt Balagopal
- 3,187
141
votes
12 answers
Why does my tea periodically alternate its rotational speed after stirring? (Link to video below)
I noticed that after stirring, a bubble in the centre of my mug of tea changed the speed it was rotating at periodically. Speeding up, then slowing down, then speeding up again, etc. Almost like when a ballerina pulls in her arms to increase her…
luke
- 1,107
141
votes
6 answers
Why do people categorically dismiss some simple quantum models?
Deterministic models. Clarification of the question:
The problem with these blogs is that people are inclined to start yelling at each other. (I admit, I got infected and it's difficult not to raise one's electronic voice.) I want to ask my question…
G. 't Hooft
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140
votes
28 answers
How can you weigh your own head in an accurate way?
I read some methods but they're not accurate. They use the Archimedes principle and they assume uniform body density which of course is far from true. Others are silly like this one:
Take a knife then remove your head.
Place it on some scale
Take…
user5402
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140
votes
11 answers
How fast does gravity propagate?
A thought experiment: Imagine the Sun is suddenly removed. We wouldn't notice a difference for 8 minutes, because that's how long light takes to get from the Sun's surface to Earth.
However, what about the Sun's gravitational effect? If gravity…
Stefano Borini
- 3,930
138
votes
5 answers
What does it mean for two objects to "touch"?
If you've ever been annoyingly poked by a geek, you might be familiar with the semi-nerdy obnoxious response of
"I'm not actually touching you! The electrons in the atoms of my
skin are just getting really close to yours!"
Expanding on this a…
Thomas Shields
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