Answer - Acceleration is the rate of change of velocity of a moving body, i.e., if the motion of a body is increasing, "acceleration"-the velocity gained per second.
Moment - of a force is the tendency of that force to produce rotation, it equals the force times its "leverage."
Center of Oscillation - That point in a pendulum where, if all its mass were collected, its time of vibration would be unaltered.
Coefficient of Expansion - A number representing the change per unit in the dimensions of a body submitted to the unit change of temperature; or, more directly, the increase per unit in the length of a body when the temperature is raised one degree.
Harmonic Motion is a periodic to and from motion such as that taken by the prongs of a tuning fork, or the motion of a very long pendulum describing very small arcs; the condition of "pure harmonic motion" being that the time occupied shall be independent of any variation in the extent of the path described, i.e., "isochronous motion."
Note - If a ball were set rolling at a uniform rate in a plane circle, on saying a horizontal table, and its motion observed from a very long distance with one's eye on the same level, it would appear to move, not in a circle, but in a straight line from left to right and from right to left; its velocity as it approaches the center, where it would be at a maximum, and decreasing as it receded from the center, till it reached the extent of its apparent path, where its apparent motion would be 0.