Holding a vibrating tuning fork close to the lip of a PVC pipe, high school student Kelsey Peterson bends close, suddenly saying, "I hear it!" She is trying to find the speed of sound indirectly, using her own measurements and a chain of logic she must forge for herself. She has learned that, as in a pipe organ, the cavity of her PVC pipe is an acoustic resonator, and the change in volume she hears tells her that it has reached the right length to resonate at the tuning fork's frequency.