motion - A change in an object’s position in respect to time and in comparison to other objects, kinetic energy - Energy of motion., speed - How fast an object’s position changes over time, potential energy - Energy that is stored in the position or condition of an object., energy - The ability to do work or to change an object. Units of energy are called joules (J), acceleration - The change in speed or direction of an object., friction - A force that opposes the motion of one object moving past another., force - A push or pull that causes an object to move, stop, or change direction., gravity - A noncontact force that acts over a distance and pulls all objects towards each other., inertia - The tendency of an object in motion to stay in motion or of an object at rest to stay at rest., magnetic force - The force between two magnets or between a magnet and certain metals. This force can push or pull., unbalanced forces - Forces that do not add up to zero. They change the motion of an object.The greater force determines the direction of motion., electrostatic force - A force that has to do with the charge an object carries. Opposite charges attract and same charges repel, balanced forces - Forces that act on an object without changing its motion. Balanced forces often point in opposite directions and always add up to zero., contact forces - A force that occurs when one object touches another., mechanical force - A push or pull that one exerts on a system’s state of rest or uniform motion,