The physics
Over a smooth pulley, a light string has the same tension T everywhere. Write F = ma for each block, along its own direction of motion. Then add the equations, and T cancels.
Atwood: a = (m₁ − m₂) g / (m₁ + m₂) T = 2m₁m₂g / (m₁ + m₂)
Table: a = (m₂ − μm₁) g / (m₁ + m₂) Slope: a = (m₁ sin θ − m₂) g / (m₁ + m₂)
Two slopes: a = (m₁ sin α₁ − m₂ sin α₂) g / (m₁ + m₂)
The pulley's support holds up two pieces of string. So it feels 2T. That is less than the total weight whenever the masses differ.