# Tag Info

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

Were you in a mountainous area? You can have that feeling due to change in elevation. Atmospheric pressure changes with elevation.

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 ...

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 ...

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 ...

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 ...

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 ...

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 $E= K + P$ ...

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: $$E_l = \frac{1}{2}m v^2$$ ...

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 ...

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 ...

0

I thought static electricity doesn't really build up when there's a lot of moisture, so that's why you don't get static shocks in the summer when there's more humidity. Even though it's winter now, I figured I wouldn't feel any static shocks if my hands are wet, but I still do. When the air contains more moisture, electron build-up on your body and ...

0

Steel balls would be a lot louder, and would have to be painted. The paint would quickly chip off from constant impacts with other (mostly) unyielding steel balls, looking skanky while providing an uneven rolling surface.

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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 ...

0

It is correct to say that a thermometer cannot measure the temperature of an object accurately.You must reflect deeply on the fact that all the laws and measurements that we have in physics are some sort of approximations .Since matter is made of elementary particles this distinction of thermometer and the body whose temperature is to be measured are itself ...

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 ...

0

It's because of how the body is oriented when going up diagonally which allows for the lateral thigh muscles to contribute to the effort, versus only the frontal muscles when going straight up. Since the effort is spread over more muscle areas, it feels less strenuous.

0

I would say this is physiological and psychological rather than dynamics phenomenon. The total work done is slightly higher when you use longer path. The work needed to increase the potential energy is the same and a tiny bit extra is taken for overcoming the (comparably very small) drag. So it feels easier rather than really being so. I can think of two ...

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 ...

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 ...

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 ...

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 ...

11

Wet wood crackles. Dry wood does not. Water in the wood boils. The steam builds up pressure because it is trapped inside. The wood explodes, releasing the steam and flying pieces.

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 ...

-1

yes, it can, because you can adjust for the mentioned effects, at least in theory.

6

Electronic energy levels are quantized. The bigger the box the electrons can move in the smaller the energy needed for a transition. H2O only contains 3 atoms (and small ones at that) so the box is small and the transitions are in the UV. The same goes for O2, CO2.

16

The human eye contains a great deal of water, so it would be difficult to see wavelengths that are absorbed by water. The light that gets to your retina has to pass through water, so the visible wavelengths of light are to a certain degree determined by what water is transparent to.

25

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 ...

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 ...

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 ...

2

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

I will try to answer your question as simply as I can but involving some biology (only a very basic thing). Now when do you see an object? Only when the light of that object hits your eyes and your eye detects it. When you look at an object, electrical signals travel via the optic nerves to an area in your brain called the thalamus. This then sends the ...

1

your room is dark because either there is not a lot of light coming into it or because all objects in your dark room absorb the light, don't reflect it back. so the light coming from the bright room does not reflect from the walls and other objects of your room, hence it's dark. in the case of the street light, it's the same. light coming from the bulb is ...

1

I don't know if you already understood it, but here is a simple explanation. Take a torchlight, look at it directly. You'll be blinded. Now, shine a nearby object, you will see the bright, but it won't hurt. Repeat the experiment with a very dim torchlight. If you look directly you will notice the light, but if you shine an object, you won't see anything. ...

1

Hello GODPARTICLE, Answer for your question lies in reflection and intensity properties of light. Here is a good article which can "throw light on your question". http://www.cs.colorado.edu/~mcbryan/5229.03/mail/97.htm Now in that article you can see figure under 1.Dull surfaces. In that figure you can replace V which is viewer with ...

1

No. The elementary idea of grounding is that excess current finds an easier way to the ground than through your body. If you're wet, you 'may' in minimal probability get a minor shock, but unless your body offers the current a path easier or at least comparable to the metallic ground wire, the answer is no. EDIT: Current gets divided in inverse ratio to ...

1

I am converting my comment into an answer with some mine amendment. You only see most of the light entering in the room which directly falls upon your eyes. On the other hand when this light coming from outside falls upon the objects placed inside the dark room then most of it is absorbed and the remaining is scattered all around, hence you see do not see ...

0

Theoretically, if you don't limit the rotational speed, The ball going halfway through and coming back out is (probably) possible. All you gotta do is spin it fast enough in the right direction and launch it at the right angle so that it hits the rim perpendicularly. The normal impulse due to the collision will generate a frictional impulse upward, which ...

0

What happens is called photoelectric effect, the microwave causes electrons in the food (specifically in the water molecules) to go away: this process leads to energy i.e heat. That's why it is not a good idea to put a metal inside the microwave. In fact Microwave is healthier because it doesn't vaporize the water molecules. Some nutrients do actually get ...

0

I've no idea if this is possible, I'm just proposing a mechanism: Microwaves heat food by causing polar molecules (eg water) to vibrate - I'm guessing you could in theory detect the equivalent of magnetisation in the foodstuff, where clusters of molecules have been left aligned by the microwaves? I doubt the effect would last long in such a noisy (hot!) ...

9

In the situation you are describing, the only thing one can take away is that the room you are in is brighter than it would be if the bright room were not there. It does not mean that your room has to be as bright as the bright room, just that your room is brighter than it would be otherwise. For your new situation with the street lamp: If you move very ...

0

Maybe it helps to approach that problem in this - somewhat "backward" way: Putting food in a microwave oven basically just heats it - in a conceptually ideal way, (if it would be uneven in practise.) But other ways to cook are way more prone to leave artefacts in the food; like brown, caramelized surface parts, or bigger parts being softer/more cooked on ...

3

You filled the hot water into the bottle, during this time it created steam inside the bottle, moving part of the air out. After closing, the steam cools down and condenses quickly. As some air was pushed out, that creates a vacuum, collapsing the bottle. Another process, which probably has contributed, but would be the main effect when the water is not ...

0

As Qmechanic noted, a question pretty similar to this has already been asked, but I figured you might be interested in a non-diffractive answer. As is obvious from women's hair-dying commercials, human hair has a small degree of reflective sheen to it, and so when you squint, it seems plausible that as the eyelashes intermesh over each other, some light ...

0

As the linked question (Qmechanic) suggests, diffraction effects cause some of that streaking. There are other cool things that can happen -- the same link mentions eyelash filter effects. I remember observing that back in the analog TV days. I could squint at a slightly noisy TV image and actually clean up the image, because I'd filtered out the ...

1

The slip ratio depends on the speed for the car you would calculate based circumferential speed of the wheel in the frame of the car (angular velocity of wheel times radius), and the actual linear speed of the car. The reason that you get slip at even the smallest forces results not from the fact that the tire is slipping against the ground, but that the ...

3

For an (idealized) perfectly round wheel on a perfectly smooth road, there is only a single point of contact between the wheel and the road at any given time. If you were to plot the motion of a single point on the wheel's surface as it goes around and then touches the ground, you would see that it follows a curve called a cycloid. The picture in that ...

1

Friction arises from the tendency or the real movement between two surfaces. when there is no slip even though the surface is not smooth frictional force vanishes because there is no relative movement at the point of contact of the wheel to the road. However this situation is ideal. if one of the surfaces could deform then the normal force from road to wheel ...

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