Tag Info

Hot answers tagged

44

Sort of, yes. Ice water is, in fact, a negative-calorie foodstuff and could be used to lose some weight. Fats contain about 37 kJ/gram of energy, drinking one glass of ice water will burn about 37 kJ or up to three times more if you eat some crushed ice as part of drinking the water: so that's 1 gram of fat burned per drink, up to 2-3 if you eat ice. The ...


28

X-rays do warm you up. It's just that the X-rays are more dangerous per photon (they can do major damage to cells and DNA, and are known to cause tumors and cancer), so they limit the amount of time you're exposed to the bare minimum needed for a clear image. The total energy from standing in the sunlight for several seconds is much higher than the energy ...


25

Yes it works. But let's not use it on a massive scale, lest we damage the ecosystem (tip of the hat to @phi1123). A hint to the mechanism can be found in Behroozi et al (Am J Phys, 2007) They state in the abstract: From the attenuation data at frequencies between 251 and 551Hz, we conclude that the calming effect of oil on surface waves is principally ...


20

In addition to the answer from @MichaelS, you need to consider where the energy from each source is deposited: Sunlight energy is deposited on/in the skin where there are numerous nerve endings. An increase in skin temperature is "measured" and your brain is aware of it. X-ray energy which is absorbed by the body is mainly absorbed by bones and some ...


10

The internal energy of an ideal gas is independent of volume when considered as a function of volume and temperature. If we choose to consider internal energy as a function of volume and some other thermodynamic variable we will find that the dependence of the energy on volume will change because we are keeping a different variable constant as volume is ...


9

Before everyone freaks out, no, you don't use petroleum oil. You use vegetable, fish or animal oil. In earlier times, whale oil would be used. The OP's picture looks like a fuel oil leak, not an attempt at wave calming. I have seen references of this technique being used since at least the early 1800s, probably much earlier. Ernest Shackleton made use of ...


6

This is a special example of "what will happen" under given circumstances. Almost all of physics – and natural science – is about answering such questions. But they're really very many very different questions and one must be a little bit more specific about what the question is. Your general question "what forms of energy will result" is so general that it ...


4

When labeling states of the hydrogen atom, one doesn't refer to the z component of the angular momentum, but rather to the total angular momentum. The total angular momentum is positive, but, as you've stated, there are two states for $J=\frac{1}{2}$ with $L=0$, and those are $J_z=\pm\frac{1}{2}$ (Or some linear combination of them) As to why this is, ...


4

The body surely needs to produce energy to heat the water one drinks - and it will heat water because almost everything in the human body is about 37 °C - but whether one loses weight in the process depends on whether the energy is taken from the accumulated fat, or from piles of extra food one devours because he or she is hungry and can't resist. ;-) The ...


4

I understand also that there would be a tiny minuscule resistive loss through the wire, but really it's not enough to say anything about. On the contrary, it's crucial. Assuming an ideal voltage source (can supply unlimited current) of voltage $V_S$, an ideal resistor of resistance $R$, and an ideal uncharged capacitor of capacitance $C$, are ...


4

You've got it a little backwards - physicists first defined the quantity $m \cdot v$ because it quantified the amount of "motion" an object possessed. They named it "momentum". Modern physics is primarily concerned with the quantity $m \cdot v$ (and the updated versions of that quantity in more recent frameworks of physics) because it is conserved. This ...


3

Even when you're hot, the body keeps producing heat, which it then goes through the trouble of shedding. Unless you were already very cold, the heat to warm your water and food intake will come out of this surplus. The body may even save energy because it doesn't need to shed as much heat. If you're wiling to be very cold all the time, you can do so more ...


3

Is it possible to measure the temperature of something using sound...? Yes, it is not only possible, it is available commercially. It is especially useful in harsh environments where conventional temperature probes might not survive. For example, TMT makes an acoustic system for measuring 2-D temperature distributions in blast furnaces: The ...


3

To get an understanding on quantum field theory issues, you have to understand the difference between virtual particles and real particles. Virtual particles, in contrast to real particles, are a mathematical construct inspired by the Feynman diagrams used to describe interactions. These diagrams start with real particles, i.e. particles that have the mass ...


3

Let's start with qft. Imagine taking the action $S$ and adding a constant. The new action is \begin{equation} S_{new} = S + M^4 \int d^4 x \end{equation} where M is a mass scale needed for dimensions. This last term in the action does not depend on any fields so it does not contribute to any dynamics. One way to express this is that the only effect of the ...


3

There's two main things to consider - energy and absorption charasteristics of different photon wavelengths. The Sun emits a lot of energy, obviously. Even at Earth's distance from the Sun, the energy concentration is still far from negligible - when this energy impacts your body and is absorbed, it mostly causes heating (a bit complicated by wavelength, ...


3

For example, the escape velocity of a particle from the galaxy is about 400 km/s and in most conceivable circumstances (unless you are basically on top of the event horizon of a black hole or on the surface of a neutron star), escape velocities will be far, far below relativistic speeds (here defined as $3\times10^4$ km/s). So basically, if a particle has a ...


2

With regards to intuition, it might help to think about situations of mechanical advantage. For example, consider a simple pulley system. modified from "Pulley1a". Licensed under Public Domain via Commons - https://commons.wikimedia.org/wiki/File:Pulley1a.svg#/media/File:Pulley1a.svg You can work out using force that the weight $W/2$ balances the weight ...


2

It seems to me that the person drawing the graph was a bit sloppy - the ideal black body radiation ("idealer Schwarzer Körper" - Temperatur 5900 K) does not cut off sharply at 240 nm as shown. Instead, it should look like this: when calculated from Planck's Law. I suspect some bug in the method used to calculate the values in the plot you reproduced - ...


2

The notion of work in physics was first formulated by the French mathematician Gustave Coriolis in Calculation of the Effect of Machines, or Considerations on the Use of Engines and their Evaluation published in 1829. Coriolis defined work as "weight lifted through a height". He was concerned with developing a term that could measure the units of work ...


2

No. The question is based on a false assumption. Nothing "seeks ground" in the sense the expression implies. Current flows in an electrical circuit. If part of the circuit is connected to "ground" then current will flow into or out of ground as part of flowing in the circuit as a whole. If you look at the "circuit diagrams" of electric circuits, in many ...


2

In addition to the other reply, it can be added that by definition, in an ideal gas, there is no interaction between molecules, and therefore no potential energy associated with the average distance. This is why in a Joule-Thomson expansion, there is no change in the temperature of the gas: only the volume changes, no work is extracted, and the average speed ...


2

As the athlete pushes off the ground, she and the luge would both be accelerating relative to the ground. This force of 500N for 5 seconds would result in a final momentum of 2500Kgm/s. If the system has 100kg total mass then you simply divide the momentum of 2500kgm/s by the mass 100kg to find the velocity which I believe is 25m/s not 250m/s. Also note that ...


2

I have a gut feeling that my reasoning is indeed faulty, but I'm unable to figure out why. If a 500N (net) force acts on a 30kg object, the acceleration of the object is $$a = \frac{500}{30} \mathrm {\frac{m}{s^2}} \approx 1.7g$$ which gives a 0 to 100 km/h time of 1.67 seconds thus beating all of the quickest supercars. In other words, there's ...


2

Yes it is possible, but the difference would need to be miniscule. Effectively your question reduces to one of the following: "does light have a truly nonzero rest mass?" and / or "is there a highly diffuse optical medium all around us which modern repetitions of the Michelson-Morley experiment have not yet detected?". Look up "Experimental Checks on Photon ...


2

General Question: Why should I use just the friction force rather than the net force to integrate over distance when conserving energy? Answer: In energy conservation problems each way of storing energy generally gets it's own term. In the example problem there is a gravitational potential energy term (GPE), a kinetic energy (KE) term, and a friction ...


2

"Thermal energy" is a bit of a misnomer because "thermal" really refers to a method of energy transfer, not energy storage. When energy moves from one system to another, it can do so via a thermal process (e.g. conduction, convection, radiation) or a mechanical process (something pushes on something else). So technically, I wouldn't call $\frac{3}{2}kT$ the ...


2

Energy is dissipated in the form of "internal energy", which means that all of the objects kinectic energy is transfered to internal movement of atoms and mollecules of both the object and the surface. When there is a large deformation and no restitution you can argue that some of the energy is stored in some kind of ellastic energy of the mollecular bonds ...


2

Calculating energies when given inverse wavelengths Frequencies are related to energies by $E = 2\pi\hbar~f$ and frequencies to wavelengths by $f = c / \lambda$, so generally if you have something which is an inverse wavelength you'd multiply by $2\pi\hbar~c$ to get its corresponding energy, while converting to a frequency like inverse nanoseconds is done ...


2

The key idea for the positive mass theorem is that asymptotically flat spacetime always has non-negative energy. Furthermore, of all spacetime which are asymptotically flat, empty Minkowski space is the only one which has zero energy. This is an important result because it tells us that spacetimes such as Minkowski are inherently stable. Now, the proof of ...



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