Reputation
850
Next privilege 1,000 Rep.
Create new tags
Badges
9 27
Impact
~63k people reached

  • 0 posts edited
  • 0 helpful flags
  • 88 votes cast
Feb
5
comment How far do we need to be removed from the earth to show the curvature with a viewing angle between 42 and 48 degrees?
If I'm standing on a beach and hold up a straight edge to the horizon, surely I'll see the horizon falling away from the straight edge. Doesn't that demonstrate the curvature of the Earth?
Jan
15
accepted Two ways of writing coordinate basis vectors confusion
Jan
15
comment Two ways of writing coordinate basis vectors confusion
Expressing basis vectors as partial derivative operators still looks weird to me, but you've answered my question. Thanks.
Jan
15
comment Two ways of writing coordinate basis vectors confusion
Sorry to be so slow, but do you mean my first equation can be written as $$\vec{e_{r}}=\frac{\partial}{\partial r}=\frac{\partial x}{\partial r}\frac{\partial}{\partial x}+\frac{\partial y}{\partial r}\frac{\partial}{\partial y}.$$
Jan
15
asked Two ways of writing coordinate basis vectors confusion
Jan
10
comment why does the higgs mechanism need to exist?
"Pleb" is a term senior Tory politicians in the UK may or may not use when asking police officers permission to cycle through the main gates at Downing Street. Possibly.
Nov
26
accepted Galileo 5 and 6 satellites testing gravitational time dilation
Nov
26
comment Galileo 5 and 6 satellites testing gravitational time dilation
Excellent link. Thanks.
Nov
26
asked Galileo 5 and 6 satellites testing gravitational time dilation
Nov
11
comment Is partial derivative a vector or dual vector?
Where does $\partial_{\mathbf v}f = \langle\mathbf df, \mathbf v \rangle$ come from? Is it a definition or can you derive it? In "Gravitation" it (Eqn 2.17) seems to be derived from some sort of Taylor Series (Eqn 2.15), but I've never seen this derivation in any other textbook. Usually $\partial_{\mathbf v}f = \langle\mathbf df, \mathbf v \rangle$ is just stated. Apologies if I'm missing the obvious.
Nov
10
comment Time taken to cook frozen peas
Must admit, I've never heard of cooking frozen peas without water. It works - I've just tried it - but you need to be careful, the saucepan gets very hot (my stainless steel saucepan began to discolour with the heat). Don't burn down the kitchen!
Nov
10
accepted Time taken to cook frozen peas
Nov
10
comment Time taken to cook frozen peas
Thanks. I thought that would be the case but didn't have the physics to back it up.
Nov
8
revised Time taken to cook frozen peas
edited tags
Nov
8
revised Time taken to cook frozen peas
edited tags
Nov
8
asked Time taken to cook frozen peas
Nov
4
awarded  Notable Question
Oct
30
accepted Derivation of one-form/vector equation in Carroll confusion
Oct
30
comment Derivation of one-form/vector equation in Carroll confusion
Hmmm, there's a lot to take in here for a plodder like me. You've been very patient. Thanks again for your help.
Oct
29
comment Derivation of one-form/vector equation in Carroll confusion
Could this be a more straightforward answer (at my level) to my question of whether $\frac{df}{d\lambda}=\mathrm{d}f\left(\frac{d}{d\lambda}\right)$ can be derived without assuming $\mathrm{\mathrm{d}x^{i}}\left(\frac{\partial}{\partial x^{j}}\right)=\delta_{j}^{i}$? Much further on (p203) they actually use Eqn 2.17 to derive $\mathrm{\mathrm{d}x^{i}}\left(\frac{\partial}{\partial x^{j}}\right)=\delta_{j}^{i}$.