Which of the following best describes gravitational force? (2 points)

an attraction between two objects that have mass
an attraction between two objects due to their electrons
the force that keeps atoms and molecules bound together
the force that keeps objects from moving when they are at rest

Which beat describes the brain stem

Which best explains how a heat pump can heat a room? cold air from the house is moved through pipes, where it absorbs thermal energy. warm air from outside is pushed into the house to replace the cold air. combustion warms the air when chemical energy is transferred to thermal energy. fuel is used to move a piston, which pushes warm air into the house.

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