I am trying to calculate the energy/ power required to move a plate up and down in a liquid.
My approach is to calculate the forces that must be applied by the motor to push/pull the plate based on Newton's law (as a function of the velocity, weight of the plate, properties of the fluid, and so on). Then to calculate Work as the product between force and displacement.
Can I say that the outcome is the required energy? Or is this a misleading assumption, based on the fact that both work and energy have the same measuring unit?
Best Answer
Yes, this is basically the correct approach. Strictly speaking, some of the energy you put in will go into heating the water, i.e., the water will get hotter as you agitate it. The energy balance would be something like:
$$ \Delta E = W + C\Delta T $$
where $C$ is the specific heat and $\Delta T$ the temperature rise. However, under most conditions, the temperature rise will be small enough that it can be ignored.