Which statement is true? a. some molecules may contain no atoms. b. some elements found in nature exist as molecules. c. some compounds include only one type of element. d. some atoms are made of two or more different elements.

The of a machine determines its "usefulness." a. input force b. output force c. mechanical advantage

If steel is more dense that lake water, why can a boat float

Which best describes how fluids change as they travel through different portions of the convection currents? they change to solids at the outer portion of the convection currents. they change to solids at the inner portion of the convection currents. they become more dense at the outer portion of the convection currents. they become more dense at the inner portion of the convection currents