Suppose you observe that at night, the air just above the ground feels cooler than the air above it. then, in the middle of a sunny day, you notice that the air close to the ground feels warmer. which process explains this? convection conduction condensation greenhouse heating

I think the correct answer would be the first option. The process that would explain this phenomenon is convection. It is a mode of heat transfer which is a result of bulk movement of a substance due to the difference in density which is a result of the temperature of these substances. This transfer of heat is applicable to fluids. When  the temperature of a fluid increases, the fluid expand thus decreasing its density. However, for a fluid which has a cooler temperature, it would contract resulting to a much higher density. Therefore, the warm fluid would rise up while the cooler fluid would sink below the warm fluid.

Ibelieve your answer is b.hope this : )

Electoral current force mechanical advantage if the wheel and axle is 2 n and the output force is 20 n