20. which of the following improves the efficiency of a machine?
cal. reducing friction
b. adding more energy
c. running it faster
increasing friction

What claim did thorne make? what evidence supported his claim?

Which of the following does not describe a physical property of iron? a iron is silvery-white or gray in color. b iron has a boiling point of about 3,000°c. c iron is a magnetic element . d iron and sulfur react to form iron sulfide.

What are some natural processes that represent physical and chemical changes?