I was reading an old thermodynamics textbook and came across this equation describing change in internal energy. What does the (dU/dT)V and (dU/dV)T mean? I think it’s partial derivatives, but I’ve never seen a derivative sub (something). Please help

Indication that the input of a multivariable function can change in many directions. Neither one of these derivatives tells the full story of how our function f ( x , y ) f(x, y) f(x,y)f, left parenthesis, x, comma, y, right parenthesis changes when its input changes slightly, so we call them partial derivatives.

explanation:

earth's surface is mainly heated by the absorption of infrared radiation from the sun.

evaporation occurs because molecules in liquid water are warmed ( usually by the sun) and vibrate quicker, becoming less dense and rise.

condensation occurs because molecules in water vapor are cooled and therefore vibrate more slowly thus becoming more dense and eventually fall to earth.

lines of equal barometric pressure on a weather map are called: isobars : lines of equal temp on a weather map are called: isotherms.​

0.19 m/s and 0.45 m/s