What will change the velocity of a periodic wave?

Changing the medium of the wave.

Explanation:

Hi, a Periodic wave is a wave with a repeating continuous pattern or cycle that the source produces.

They are determined by the properties of the medium. So, if we change the medium of the wave It´s velocity will change.

The mediums are distinguished by their properties - the material they are made of and the physical properties of that material such as the density, the temperature, the elasticity, etc.  

Feel free to ask for more if needed or if you did not understand something.

hi there if you are asking for conformation that wavelingth is the correct answer is wrong it is the answer is frequency. : )

i hope this you out, have a wonderful day

answer would be letter choice (a),   a ball resting on a shelf. would be another example of potential energy   >   stored energy > not moving.

a ball spinning on a finger   >   kinetic energy > moving energy

a ball rolling on the ground   >   kinetic energy   > moving energy

a   ball flying through the air   > kinetic energy   >   moving energy

hope that                                         : )