How fast does sound travel through plastic at 25 degrees Celsius?

Answer 1

Average speed of sound in silver at standard conditions (25°C, 1 atmosphere) is about 2680 m/s, that is about 7.7 times the speed of sound in air.

However, while air is a gas, that is an homogeneous and isotropic material (its characteristics do not depends on the particular point where they are measured or on the direction if the external conditions are uniform), this is not true for silver.

At standard conditions silver is a crystal, so being anisotropic in space. This means that the material characteristics depends on the direction, so that the speed of sound depends on the direction of propagation of sound itself and on the type of sound wave that is considered.

As a matter of fact, sonic waves can be transverse (the material oscillations are along a direction orthogonal to the propagation direction) or longitudinal (the material oscillations are in the same direction of propagation).

This justify the fact that 2680 m/s is the average speed of sound, averaged with respect to the propagation direction and the type of wave.

Depending on direction and type of waves, the sound speed varies between 3704 m/s e 1698 m/s.

Answer 2

Plastics are a range of materials and the speed of sound varies according to the plastic. It is approx 1060 metres per second at 25 deg C in PVC and 1430 ms^-1 in acrylic.