A pendulum swings above a table. The table itself is also a pendulum that swings at right angles to, and has the same period as the first pendulum. When both pendulums are set swinging at the same time, the observer sees the relative motions of the two pendulums in the frame of reference of the table. The relative motion can be linear, circular or elliptical, depending on the phases and amplitudes of the pendulums. The visitor starts the pendulums swinging and controls their relative phase. Pendulum/Relative Motion illustrate how two sinusoidal motions at right angles add together. It can be used to explain polarization of light which can be linear, elliptical or circular, and which can be considered as a combination of two components at right angles to one another. It is startling to hold a flat object next to the first pendulum and see that its motion is indeed back and forth in a straight line when it looks like it is moving in a circle.