These two scientists grossly underestimated the age of the Sun by assuming that it only produced heat through gravitational contraction. For 10 points each:
[10m] Identify these two scientists who name a mechanism by which bodies such as Jupiter contract and give off heat due to gravity.
ANSWER: Lord Kelvin and Hermann von Helmholtz [or William Thomson, 1st Baron Kelvin in place of "Kelvin"; or Kelvin-Helmholtz mechanism]
[10h] Kelvin and Helmholtz also name a fluid instability that occurs when this quantity has different values across a boundary. This quantity has a divergence of zero for incompressible flow.
ANSWER: fluid velocity [or flow velocity or speed]
[10e] That instability causes a rolling, wave-like shape in the Kelvin-Helmholtz type of these features. These atmospheric structures also have cirrus, stratus, and cumulus types.
ANSWER: clouds
<June Yin , Science - Physics - Fluids>