force: Some outside influence that can change the motion of a body, hold bodies close to one another, or produce motion or stress in a stationary body.
gravity: The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.
Isaac Newton: This English physicist and mathematician became most famous for describing his law of gravity. Born in 1642, he developed into a scientist with wide-ranging interests. Among some of his discoveries: that white light is made from a combination of all the colors in the rainbow, which can be split apart again using a prism; the mathematics that describe the orbital motions of things around a center of force; that the speed of sound waves can be calculated from the density of air; early elements of the mathematics now known as calculus; and an explanation for why things “fall:” the gravitational pull of one object towards another, which would be proportional to the mass of each. Newton died in 1727.
mass: A number that shows how much an object resists speeding up and slowing down — basically a measure of how much matter that object is made from.
physicist: A scientist who studies the nature and properties of matter and energy.
resistance: (in physics) Something that keeps a physical material (such as a block of wood, flow of water or air) from moving freely, usually because it provides friction to impede its motion.