# Tagged Questions

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### Feynman Diagrams: Mass Conservation

Can a Feynman diagram end with more matter than it began with? The answer should be no because it would break the law of conservation of mass, right? Example: I learned that two up-quarks could ...
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### What are the forces used in this weightlifting example? [closed]

You have a person doing a bench press. Their hands are equidistant apart and they are centered on the bar - each hand about 1.5 feet from center of the bar. The bar weighs 45 pounds. In example 1 ...
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### Barbells and gravity

A giant set of bar bells floating in space (like two identical sized planets connected by a long rod) would have a centre of mass midway between the two on the connecting rod. But surely it would ...
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### Stability of balanced masses with different surface areas

Say I have this setup. The two round objects have equal mass and their centers of gravity at the same distance from the shaft. The objects only differ in that they have different surface areas ...
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### Flow of freezing liquid or a melting solid

If a liquid is freezing, is equation of continuity violated? As the liquid flows, some portion of it is getting frozen. The mass of the fluid thus keeps dropping. Similarly, when a molten fluid flows ...
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### The role of dark matter in black holes and star formation

In my understanding, there exists a critical mass for which a star needs to be in order for it to collapse into a black hole. This also applies to a certain critical density of gas in order for stars ...
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### Can we explain physical similarities between Black Scholes PDE and the Mass Balance PDE (e.g. Advection-Diffusion equation)?

Both the Black-Scholes PDE{*} and the Mass/Material Balance PDE have a similar mathematical form of the PDE which is evident from the fact that on change of variables from Black-Scholes PDE we derive ...
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### Is this static mechanical balance possible without trickery?

On damnlol.com, I came across this picture: http://www.damnlol.com/hello-god-i-have-a-fault-to-report-7549.html My question is: Is this possible without glue? If not are there similar situations ...
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### Explain how (or if) a box full of photons would weigh more due to massless photons

I understand that mass-energy equivalence is often misinterpreted as saying that mass can be converted into energy and vice versa. The reality is that energy is always manifested as mass in some ...
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### What are the ideal centers of mass and rotation for a steadicam?

For those who don't know what a steadicam is, I'll explain it in two points to give a basic idea. If you know what a steadicam is, skip to point 3. 1) A steadicam is a stabilizing mount for a motion ...