[ Mass ]
The mass of a body measures the force needed to move it orto change the way it moves. Mass is often measured by weighing thebody, but mass and weight are not the same. The weight of an objectis the force attracting it to another object, such as the Earth or theMoon, and it depends on the mass of both objects and the distancebetween them. You weigh slightly less on top of a mountain becauseyou are farther from the center of the Earth. - P99
[ E = mc² ]
Einstein was a German physicist who was born in 1879. Hediscovered that energy is equivalent to mass, according to the famousequation E=mc², where "E" is energy, "m" is mass, and "c" is thespeed of light. Because the speed of light is very large, Einstein andothers realized that this equation suggested one could make an atombomb, in which a small amount of mass is converted into a very largeamount of energy in an explosion.
Einstein also discovered that mass and energy curve space,
creating gravity. - P99