Tag Info

Hot answers tagged

52

This behaviour is well explained by Barlow's formula, even though the English Wikipedia article is incomplete in this context. The German version, on the other hand, gives the full picture (which I will quote in the following). The walls of a pipe (or a similar cylindric container, say, a sausage) experience two types of stresses: Tangential ...


26

Water is not transparent for deepUV and infrared. From the evolutionary point of view our eye developed to see electromagnetic radiation present at earth in the past (and now) - deep UV and infrared are absorbed by water vapor and other gasses in atmosphere - so there were nothing to see at these wavelengths. Here is a nice explanation on why some things ...


17

There is a great paper from the group of Howard Stone on this subject: Wetting of flexible fibre arrays (freely available here, but for some reason I am not allowed to link to it normally: http://211.144.68.84:9998/91keshi/Public/File/34/482-7386/pdf/nature10779.pdf) They specifically study when 2 closely positioned parallel fibers (i.e. hairs) clump ...


14

I'll have to take a page from my EE background and say it's because of the path of least resistance. If you look at the end of a sausage, there is already tension along that plane, in multiple locations: A chain is only as strong as its weakest link (see what I did there? :) ), so it's natural for a hot dog/sausage to split along a path that's already ...


11

To answer this question we also need to know why some things are not transparent and why certain things, water for example, don't behave in this way. A substance's interaction with light is all about interactions between photons and atomic/molecular electrons. Sometimes a photon is absorbed, the absorber lingers a fantasctically short while in an excited ...


7

This isn't the definitive answer that DumpsterDoofus was hoping for since I can't point to any scientific publications - they must exist but a quick Google failed to find anything from a reputable journal though there are loads of blog articles. Anyhow, although in soda the carbon dioxide solution is supersaturated there is an energy barrier to creating a ...


5

When you compute the energy of a rotating object you either consider the tangential velocity or the angular velocity. The two expressions are two different ways to look at the same observable, they both lead exactly to the same result and summing them is a mistake. For instance for a point like mass on a straight line we have: $$E_l = \frac{1}{2}m v^2$$ ...


4

No, it does not gain energy. The confusion arises because there's a force that does no work. If the car moves a distance $d \vec l = \vec v dt$, then the work done during that time $dt$ is $dW_{rope} = \vec F_{rope}\cdot d \vec l= 0$. This follows because $ \vec F_{rope}$ and $d \vec l$ are always perpendicular to each other (draw and check this!) which ...


4

When you look at this video you can see that the lower leg seems to maintain a constant velocity. This is probably partially due to the higher total mass of the leg compared to the ball. The ball leaves the foot at a higher velocity. This due to the deformation of the foot and the ball. This deformation is caused by acceleration (initial velocity ...


4

There exists coherent light and incoherent light The laser is an example of coherent light, i.e. it can be described by a wave with a known amplitude and phase . Amplitude is connected with the power that the beam distributes. In lasers this is very concentrated . Amplitude is also connected with the number of photons in the beam . The street lamp is an ...


2

John Rennie's answer is pretty good. I will only add the reason for the energy curve is the different forces between adjacent molecules. And this mean different potential energies. H2O - H2O and CO2 - CO2 are more energetically favorable than H2O - CO2 CO2 - CO2 is found in the interior of a bubble. The energy drop is proportional to the number of ...


2

Helicopter rotor is a rotating wing. It produces lift the same way aircraft wing does, but instead of relying on forward motion of the aircraft it has it's own motion. The lift generated depends on coefficient of lift, air density and forward speed. Formally $L = \frac{1}{2}\rho v^2\alpha C_L$ where $L$ is lift force, $\rho$ is air density, $v$ is forward ...


2

Your description of the disturbance wrought on the system by the thermometer is sound. You may be able lessen the effect with a thermal diffusion model of the thermometer and by calculating what the system's temperature was before it brought the thermometer into equilibrium with itself, but for that approach to work, one must know the system's heat capacity ...


2

Earth is only about 3% closer to the Sun in the winter, which means its intensity would only increase by a maximum of about 6%. There is more atmosphere to block out the UV rays that cause tanning and burns due to the shallower angle of incidence. You tend to wear more clothing (gloves, scarf, etc) that blocks the rays. It's cold, so I doubt a lot of people ...


2

It may actually work, as evaporating liquids need heat to evaporate, and water will somewhat evaporate even in the fridge. I am not sure it works in practice, because the paper also causes an adverse effect, it provides insulation, Hard to tell which effect is dominant. I'm pretty sure that the balance of both effects depends in a very large part on the ...


2

Sudden change in athmosferic pressure due to several reasons. You can reproduce that effect by opening the roof hatch or rear seat side window wile driving. Though, I am not capable to describe all the fluid dynamics going on there. I am guessing that due to aerodynamical features of the car, there's lowered air pressure near rear windows or behind roof ...


1

This is due to a psychological effect known as Color constancy. Your brain seems to see something based on the context around it, for instance the blue image projected on the red wall may be more black than blue but your brain will compensate for some of that because you also see the red wall. This is also the source of a number of related optical ...


1

I believe the 'urban legend' you are referring to is about cooling a bottle when you do not have a refrigerator. On a hot and windy day you could store your bottle in the sunlight, but it would be better in the shade, but if you really wanted to cool the bottle by a few more degrees, the 'myth' says wrap it in wet paper or cloth. During the time when the ...


1

Doppler shift occurs only when the sender, the receiver or both are moving relatively to each other. As the black boxes rest at the bottom of the ocean and the search ships move relatively slow, there won't be any significant Doppler shift. However, if the Ocean Shield receives several signals at different locations (the location of the Ocean Shield), the ...


1

That's because the sun is shooting the light at such a small angle that the light have to travel trough the atmosphere for a longer distance. And the atmosphere will decrease the luminosity of the sun. If we could move with the earth in the outer space without rotation, then we would find that the sun is flying upward and downward, drawing a sine wave in the ...


1

The potential energy $ P $ of the car doesn't change (the car stays on the ground the whole time), and because it moves uniformly in a circle, its speed $\left | \mathbf{V} \right |$ doesn't change. But the kinetic energy $ K $ of the car is $\frac {1}{2} m\left | \mathbf{V} \right |^2 $, so it doesn't change aswell. Hence, the total energy $ E= K + P $ ...


1

$\def\om{\omega}\def\vr{{\vec r}}\def\l{\left}\def\r{\right}\def\ve{{\vec e}}\def\vom{{\vec\omega}}\def\ds{\,'}$ Let the car move in the (x,y)-plane, let $m$ be the car's mass and let $J$ be the moment of inertia for the rotation about the axis through the center of mass aligned parallel to the z-direction. If you have a straight line and a circle with ...


1

I think that you can state that it can not measure the temperature of a substance before it have been test but it can measure the temperature after it have come in equilibrium with the substance. For example, in an experiment that need to push a liquid to T temperature, what you do is heat up the liquid with the thermometer already inside. With this you ...



Only top voted, non community-wiki answers of a minimum length are eligible