Do solid objects or structures vibrate as a whole macroscopically?

Question

I know particles vibrate in a solid microscopically, but the solid object itself does not vibrate right? Does the microscopic vibrations cause the solid object to vibrate macroscopically?

Answer 1

In a solid, particles do indeed vibrate at the microscopic level due to thermal energy. This microscopic vibration is known as thermal motion or lattice vibrations. While individual particles are in constant motion, the entire solid object does not necessarily vibrate macroscopically in the sense of visible oscillation.

However, the microscopic vibrations of particles contribute to the macroscopic properties of the solid. These collective vibrations affect the overall behavior of the material, influencing its thermal, mechanical, and electrical properties. The motion of particles at the microscopic level can lead to phenomena such as expansion with temperature increase, transmission of sound waves, and changes in the material's state.

While the solid object itself may not exhibit visible macroscopic vibrations, the cumulative effect of microscopic vibrations contributes to the macroscopic properties and behavior of the solid. The relationship between microscopic and macroscopic vibrations is a fundamental aspect of understanding the thermal and mechanical characteristics of materials.

Answer 2

Hailey,

I guess your question is about the case where the solid is either "isolated" from all external forces (or the net external force on the solid is zero)

Then it CANNOT vibrate as a whole. Because in such case the velocity V_cm of the body's center of mass would change in time. That would violate the linear momentum conservation Law b/c the solud's momentum P=MV_cm where M is the mass of the solid is

BTW. That means that the vibrations of atoms inside the body CANNOT all be in phase. Rather they at any given moment be correlated in such a way that the net change of the velocity of the center of mass should remain zero.

Hope it'd clarify

Best

Dr.Ariel B.