hello, I have a couple questions about #physics more precisely #relativity

How do I actually use #metric #tensors? Do I just do a dot product over the elements with a vector? If a metric tensor has a variable inside, does that variable comes from the vector and I just replace it? After I replace the vector and do the equation, only then I do the dot product?

If I want to have the inverse of a metric tensor, do I just do a #matrix inversion?

#physicsquestion #pleaseboost #pleaseboostme

Question: What is the derivative of the Lagrangian (of what system I don't particularly care right now) with respect to entropy (or to the time derivative of entropy)? Is this even a sensible question? Can we use the Euler-Lagrange equation for entropy?

#lagrangian #lagrangianMechanics #physics #physicsQuestion #entropy #eulerLagrangeEquation #eulerLagrangeEquations

Turns out infrared thermometers don't get the temperature of water right.
Alerted to this when dying a shirt.
IR thermometer said 85°C - while I wondered why the water was gently bubbling.
Digging out a mercury thermometer revealed why - it was at simmering at 100°C.

The shirt still seems to have dyed okay.

Any physicist care to explain?
#PhysicsMastodon
#PhysicsQuestion
#IRThermometer
#TheNeedForPurple

@gmusser Consider using a hashtag like #physics or #physicsquestion

Physics friends: When you fill a water bottle from a tap quickly, there’s an audible frequency sweep (to higher frequencies). Why? Can you write an equation for it? #physics #PhysicsQuestion