Question

eli creates longitudinal waves in the spring toy.
select the true statements about longitudinal waves.
the matter that a longitudinal wave travels through is called the medium.
if a longitudinal waves frequency decreases and its speed stays the same,
its wavelength decreases.
in a longitudinal wave, the wave and the particles of matter move in
parallel directions.
if a longitudinal waves frequency increases, the energy carried by the
wave increases.

Explanation:

• For the first statement: In wave - related concepts, the medium is indeed the matter through which a wave travels. For longitudinal waves (like sound waves in air or the wave in the spring toy), the medium is necessary for the wave to propagate.
• For the second statement: Using the wave equation \(v = f\lambda\) (where \(v\) is speed, \(f\) is frequency, and \(\lambda\) is wavelength), if \(v\) is constant (\(v = f_1\lambda_1=f_2\lambda_2\)), when \(f\) decreases (\(f_2 \lambda_1\)). So this statement is false.
• For the third statement: In a longitudinal wave, the particles of the medium oscillate parallel to the direction of wave propagation. For example, in a sound wave (a longitudinal wave), air molecules vibrate back - and - forth in the same direction as the sound wave travels.
• For the fourth statement: The energy of a wave is related to its amplitude, not directly to its frequency (for a given medium). For example, a soft sound (low - amplitude sound wave, a type of longitudinal wave) and a loud sound (high - amplitude sound wave) can have the same frequency but different energies. So this statement is false.

Answer:

• The matter that a longitudinal wave travels through is called the medium.
• In a longitudinal wave, the wave and the particles of matter move in parallel directions.