Here's why:
* Wavelength is the distance between two consecutive crests (or troughs) of a wave.
* Frequency is the number of waves passing a point per second.
* Speed of the wave on the spring is determined by the properties of the spring itself (tension and mass per unit length).
The relationship between these is:
Speed = Frequency x Wavelength
When you shake the spring more slowly, you are decreasing the frequency. Since the speed of the wave is constant, the wavelength must increase to maintain the balance in the equation.
Think of it this way: if you shake the spring slowly, you are creating fewer waves per second. To cover the same distance, each wave needs to be longer.
