A typical stellar spectrum (a plot of intensity versus wavelength) includes a number of deep indentations in which the intensity abruptly falls and then rises. These deep indentations are called lines.

When a book falls from a shelf to the ground without anyone pushing on it, no work is done on the book. true or false

The percent efficiency of a machine can never be 100% (or greater), because in the real world some energy is always converted into a. heat b. work c. input force d. output force

Which of the following are properties of mechanical waves? check all that apply ⭕️ particles of the medium move back and fourth, but do not move with the wave. ⭕️ the particles of the medium always move parallel to the wave motion. ⭕️ wave motion begins with a disturbance in the medium. ⭕️ waves transport energy from a source outward, away from the source.