It would be impossible to perform a controlled experiment on which of the following objects? a. two types of food
b. zebras in a zoo
c. the solar system
d. a piece of metal

When the force acting on an object points at least partially in the direction of the motion the work done is considered to be negative

Air is contained in a variable-load piston-cylinder device equipped with a paddle wheel. initially, air is at 400 kpa and 17°c. the paddle wheel is now turned by an external electric motor until 75 kj/kg of work has been transferred to air. during this process, heat is transferred to maintain a constant air temperature while allowing the gas volume to triple. calculate the required amount of heat transfer in kj/kg.

What was the first instrument to ever record an earthquake?