Explain if the efficiency of a machine can ever be greater than 100%?

List four observations that indicate that a chemical reaction may be taking place

What is an example of a physical property?

Which of the following is an example of physical change not a chemical change? a) a log gives off heat and light as it burns. b) a tree stores energy from the sun in its fruit. c) a penny lost in the grass slowly changes color. d) a water pipe freezes and cracks on a cold night.