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what is an endothermic and exothermic reaction? ?

Efficiency is the percent of work put into a machine by the user (input work) that becomes work done by the machine (output work)

The phlogiston theory in the 17th century attempted to explain burning. the theory stated that combustable objects contained a material called phlogiston, a substance without mass, color, odor, etc. after objects burned, the objects were dephlogistonated and were then in their true form. the phlogiston theory was accepted until the 18th century, when lavoisier proved that combustion requires a gas that has mass. phlogiston is considered a) to be scientific knowledge b) not to be scientific knowledge c) to be proven by scientific method d) to be accepted in the modern scientific community

How does friction with the atmosphere affect the speed of an artificial satellite