# Tag Info

### In stress-strain diagrams, why is the dependent axis ($y$) used to represent stress and the independent axis ($x$) to represent strain?

Because the equipment used to measure stress-strain curves works by applying a strain that increases linearly with time and measuring the stress. The strain is the independent variable. The problem ...
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### Why does the Strange Quark have Strangeness -1?

From the Wikipedia article Strangeness: The terms strange and strangeness predate the discovery of the quark, and were adopted after its discovery in order to preserve the continuity of the phrase; ...

### Fourier Transform of a Wave Packet

Mathematicians usually put $1/\sqrt{2\pi}$ before each integral. Physicists usually leave it out of the integral like your first equation, but then divide the inverse integral by $2\pi$
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Accepted

• 7,006
1 vote

### What is a rigorous and general definition of the parity operator?

Parity is a discrete spacetime symmetry under which the spatial coordinates $x^i$ transform as $x^i \rightarrow -x^i$ and the time coordinate transforms as $t \rightarrow t$. Various fields also ...
• 33.3k
1 vote

### Why does the Strange Quark have Strangeness -1?

The sign of additive quantum numbers is set up to a convention. Take for example the case of the electric current: we use to say in electronics that current is a positive flow of charge, that is a ...
1 vote

### Covariant vs. contravariant definition of the Energy-Momentum tensor

The metric $g_{\mu\nu}$ can be used to raise and lower indices. In this case you are lowering the indices on the SEM tensor, that is converting it from contravariant to covariant. So the answer is ...
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