How to control sound energy/waves?
Sound energy travels through waves by bouncing from hard surfaces to another. Echo is an example of bouncing sound energy. It happens because of hard objects inside a room or for example because of the vacancy of a certain place. You can be able to stop its waves using soft materials disabling sound’s ability to bounce. Try to conduct your own experiment in a vacant room. First leave it empty then shout. Secondly, put curtains covering the wall of the room. You will come up to an idea that sound waves move freely in an area surrounded by hard surfaces and materials and is controllable inside a place where it can’t be able to bounce. I hope this helps you..
Why is sound produced when two objects collide?
The contact force between two objects is nonlinear and piecewise (typically Hertzian). This type of force results in a very short peak of force (a pulse). Such a sharp peak contains energy at a broad range of frequencies, which excite the resonances of the two bodies that collide. The bodies then keep resonating and their vibration radiates sound in contact with the air, this is most of the sound that we hear. Depending on the bodies, the sound will be different (Think of a Xylophone being struck by a mallet, the different bars produce different sounds), because they have different resonance frequencies.