The motion of the prongs of a sounding turning fork is

Step 1: Analyze the question We are asked what type of motion the prongs of a sounding (vibrating) tuning fork undergo.

Step 2: Explain the concept When a tuning fork is struck, its prongs move rapidly back and forth about their rest (equilibrium) positions. This repeated to-and-fro movement along a path is called oscillatory (vibratory) motion. It is the same kind of motion as a pendulum bob swinging or a mass on a spring. The prongs' vibration disturbs the surrounding air and produces sound waves of a definite frequency.

Step 3: Eliminate the options

• A. Circular: the prongs do not move in a circle around a point.
• B. Oscillatory: the prongs move to and fro about a mean position. This fits.
• C. Random: the motion is regular and periodic, with a fixed frequency, so it is not random. (Random motion describes things like gas molecules in Brownian motion.)
• D. Rotational: the prongs do not spin about an axis.
• E. Translational: this means moving from one place to another in a straight line, but the prongs stay in place and only vibrate.

Step 4: Answer The motion is oscillatory, which is option B.

Exam tip: Whenever you see "sounding", "vibrating", "to-and-fro" or "about a mean position", think oscillatory/vibratory motion. Sound sources (tuning forks, guitar strings, drum membranes) all vibrate.