A fifth-grade student fastened a piece of cardboard to his bicycle wheel so that the spokes would cause the card to vibrate. When the student rode the bike fast, the student heard a high pitch. When the student rode the bike slowly, the student heard a low pitch. Which BEST explains why the student heard both high and low pitches from the cardboard?
The vibrations were faster when the student rode slowly.
The vibrations were slower when the student rode faster.
The cardboard vibrated at the same speed.
The cardboard vibrated at different speeds.