Hot answers tagged everyday-life
49
Ice cubes have three distinct cooling effects:
The cube, initially at sub-zero temperature, absorbs some heat to reach fusion point (0⁰C).
The cube absorbs more heat to switch phase: it takes some energy to turn 1 kg of ice at 0⁰C into 1 kg of liquid water at 0⁰C.
The water absorbs some heat to become warmer than 0⁰C.
The three effects occur more or less ...
42
This is a statics problem.
Assume the cable is static, perfectly straight and horizontal.
Pick any point on the cable and the sum of the forces on that point must equal zero.
There is a force, due to gravity, "downward".
So, there must be an equal, opposing force "upward". This upward force must come from the tension in the cable.
But, if the cable is ...
32
Play-Doh is mostly flour, salt and water, so it's basically just (unleavened) dough. There are a lot of extra components like colourings, fragrances, preservatives etc, but these are present at low levels and don't have a huge effect on the rheology.
The trouble with saying it's basically just dough is that the rheology of dough is fearsomely complicated. ...
29
Use a prism (or a diffraction grating if you have one) to break up the light coming from a florescent bulb. You'll see a bunch of individual lines rather than a continuous band of colors. This comes from the discrete energy levels in atoms and molecules, which is a consequence of quantum mechanics.
If the audience you have in mind is more advanced, you can ...
17
When you look at a surface like sand, bricks, etc, the light you are seeing is reflected by diffuse reflection.
With a flat surface like a mirror, light falling on the surface is reflected back at the same angle it hit the surface (specular reflection) and you see a mirror image of the light falling on the surface. However a material like sand is basically ...
15
The two "no" answers you've already received are correct for all practical purposes.
In real-world cases there can be a difference though. The difference depends on when the refrigerator decides to cycle on and cool. If the fridge cycles on a timer or based on heat energy then there will be a difference due to the added heat capacity. The outside of the ...
15
The Lorentz force $\textbf{F}=q\textbf{v}\times\textbf{B}$ never does work on the particle with charge $q$. This is not the same thing as saying that the magnetic field never does work. The issue is that not every system can be correctly described as a single isolated point charge
For example, a magnetic field does work on a dipole when the dipole's ...
14
The surprising answer is that the stability of the modern bicycle has little or nothing to do with centrifugal force or gyroscopes or any of that. Look up "bicycle stability" on Google. Experiments show that the sloped angle of the front fork is very important, e.g. If the fork pointed backwards it is very difficult to stay upright at any speed.
At ...
14
Magnetism is a nice example, you can explain the spin-spin alignment only with quantum mechanics (see exchange interaction), it is even possible to prove the Bohr-Van leeuwen theorem, which states that no classical theory can explain how a magnet works.
Reference: Feynman's Lectures on Physics
12
Here is an explanation by Bo Danforth:
Shown in the picture above is a segment of a Wurlitzer jukebox bubble tube. In the tube, the bubbles rise as expected, but as they approach the top, odd things begin to occur. Instead of remaining the same size as one might think, or increasing slightly from a minute reduction in pressure, they instead decrease in ...
11
This problem is very simple, but it's easy to overcomplicate by looking at too small a scale. At every second – no matter what the heater does – you waste money by heating the outside of your house. The rate of heating – and thus the rate at which you waste money – is given by Newton's Law of Cooling. So
$$ \text{Wasted money} \propto \int ...
11
A fundamental principle of thermodynamics is that heat flows from warm places to cold ones, through either convection, conduction or radiation, and it will continue to do so until the temperature equalizes across the system.
The stones are colder than the whiskey when you put them in the glass, so as the system heads towards equilibrium, the whiskey gets ...
10
A report appeared in Science today which addresses this exact question: Kooijman et al., Science 332 (6027): 339-342, "A Bicycle Can Be Self-Stable Without Gyroscopic or Caster Effects."
The abstract reads:
A riderless bicycle can automatically steer itself so as to recover from falls. The common view is that this self-steering is caused by gyroscopic ...
10
In fresh water what makes lightening so dangerous to a swimmer is that most of the current travels on the surface of the water, so rather then getting a $1/r^2$ falloff in current density, you see a $1/r$ falloff. Obviously eventually it will be conducted down into the mass of the water, but this takes a many meters. In salt water, this should happen much ...
10
The thing is that paper fibers are really transparent (unless the paper has been painted some color, of course). The only reason paper blocks light is that its fibers are all “immersed” in air.
Try to imagine what you would see with a very potent microscope: various clear tubes going in all directions. What happens to a ray of light entering this maze of ...
10
The heat loss (power) at a particular temperature is the same. So, No - the cooling needed to maintain the thing cold stays roughly the same.
However, the empty fridge has lower total heat capacity. So, it will get warm faster in the absence of power. So, it is worthwhile to fill your fridge and freezer with bottle of water a few days before a big storm ...
10
AC or DC, you only get electrocuted if current passes through your body. (Current passing through any part of your body can be dangerous, and possibly cause an electrical burn, but current passing across your heart is the one that's really dangerous.) Touching just one wire at a time gives the current nowhere much to go. You are right to think that some ...
10
Imagine a heavy chord raised off the ground between two blocks. Rather than consider all of the mass pieces of the rope, and the forces on them, we can simplify the problem a little bit by considering a slightly different one.
The chord can be represented by a heavy ball (in the middle of the chord) connected by two massless strings to the blocks. From ...
10
It's funny that you mention "the naked eye", because all you have to do is to close your eyes. As it turns out, the reason why we don't see anything when we close our eyes is quantum mechanics.
Sean Carroll explains it nicely: There is a lot of black body radiation in the infrared range inside your eyes. Even though the total energy of this infrared light ...
9
To prove that experimental Physics is alive and well, I used my kitchen scales to measure the force needed to click the button on my mouse, and it turned out to be 100g i.e. 1 N plus or minus about 10%. The distance the button moves is about a millimeter i.e. 0.001m, plus or minus 20% (OK - you try measuring it without a micrometer to hand) so the work per ...
9
TL;DR: Whiskey stones work by absorbing heat from the whiskey in an attempt to reach thermal equilibrium1.
As Thomas mentioned, ice has three cooling effects:
Ice itself takes 2.11 kilojoules of heat per g to have its temperature increased by 1 degree (Celsius). This number is known as "specific heat capacity"
Ice takes 334 kilojoules of heat per kg at 0 ...
9
Of course it has something to do with the liquid water entering the gas phase just above the cup of tea, but how does that give the bag of tea a directed motion to one side?
Nope.
The teabag is dangled by a string. Remember that the string is made of wound up threads:
Now, the threads stay wound up because they fit well and they have a knack of ...
9
The premise of the question is not correct, but there is a general shape to rivers.
From Leopold and Langbein, writing in Scientific American:
A sample of 50 typical meanders on many different rivers and streams has yielded an average value for this ratio of ahout 4.7 to one.
The ratio they use in that article is different from the definition you ...
8
Here's a crude way to look at the problem:
Suppose there are $N$ wires. Each has resistance $R$, common potential difference $V$ and are connected in parallel. So the current through each wire is $I = \frac{V}{NR}$.
Let's imagine a hypothetical wire formed by sea water which has a length, $L$ and cross sectional area, $S$. There are approximately ...
8
It seems we have reached the point where simple models are no longer satisfying. Rather than posing ad hoc DEs maybe it's time to try an actual physical model. Short of doing a full hydrodynamic simulation (definitely overkill here) we can try what is called a lumped capacitance model where we divide the system up into a number of "lumps" and energy flows ...
8
No. The rate of cooling must simply match the rate of heating, and heating rate depends only on the temperature difference you want to establish and on the thermal conductivity and surface area of the walls.
More stuff in the refrigerator would give it a higher heat capacity, so that it wouldn't warm up so much when the door is opened. However, it will take ...
8
Reflections on Everyday Quantum Events
In one sense, it's hard not to see quantum mechanics in everyday life. For example, the existence of complex chemistry and the volume occupied by ordinary matter are both direct consequences of something called Pauli exclusion. That's a quantum rule that requires that every electron in the universe maintains a unique ...
7
I have read that true steam is clear (transparent) water vapor. According to this theory, the white "steam" you see is really a small cloud of condensed water vapor droplets, a fine mist in effect. So what you are seeing is not more steam, but more condensation and more mist. The speed with which the steam/vapor/mist rises and disperses may also change.
7
Please note that the following is all conjectural. I only volunteer it due to the lack of other responses after numerous days, the coolness of the question, and the probably lack of people/references who are explicitly experienced with this specific topic.
Basic Picture
As a general relation, I'm sure one can correlate the sound-volume with the total ...
6
It's not a disturbance, the liquid isn't supercooled in this case. It's right about at 0 degrees, though.
It isn't the pressure drop directly, because you can give an upper-bound estimate to how much cooling the pressure drop directly does based on the observation that the pressure is not more than a few atmospheres. That means that space the gas in the ...
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