Imagine giving a quick gentle kick to a small wooden block resting on a frictionless table. It starts moving. I'm wondering if all the atoms/molecules of the wood start moving at the same time... I'm not sure if it takes some time for the atoms on the other side to feel the kick. I'm familiar with newton laws but I think newton laws treat the object as a point mass and don't really care about how the force is perceived by the atoms/molecules/lattice of the object. If possible I'm trying to have a simple explanation of how the force propagates from one side to the other side, and why the object starts moving in a straight line, instead of oscillating left and right or doing some other thing.
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If the body is elastic and you treat it as a continuum, then the deformation of the body is governed by the wave equation, involving the modulus of elasticity of the material and its density. See the following current thread: Solving a continuum-mechanical model At the end where you kick the object, you initiate a compression wave which travels through the object at the speed of sound in the material. Behind the wave front, the material is compressed and traveling a finite velocity. Ahead of the wave front, the object is still stationary, and traveling with zero velocity. The compressive strain behind the wave front is equal to the velocity divided by the speed of sound in the material.
Chet Miller
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Atoms are bound together in a solid by being in perfect balance between repulsion and attraction forces - a bit further away, and they are pulled back in; a bit closer, and they are push back. This electromagnetic force between atoms propagates at the speed of light.
Is the object perfectly rigid, then the only delay in the force transfer from particle to particle comes from these inter-atomic electromagnetic forces. The particles at the other side feel the push at the speed of light.
Is the object elastic (or deformable), then energy is absorbed throughout. The force is then not transmitted fully but is damped and slowed down along the way (it is "spent" on moving particles rather than transmitted). Force is still transmitted between particles at the speed of light, but particles might move at much slower speeds before bumping into the straight-line neighbour.
- An elastic structure is for example a rubber band where curled-up chains of molecules are stretched out as if they were springs, which allows the whole material to elongate - the force is "spent" on stretching these chains.
- A deformable structure like a soft pillow might have large voids in-between particles. Force is again "spent" on moving particles around, in this case rearranging them permanently.
Steeven
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It is true that in solids the atoms and molecules of the lattice are held together in a quantum mechanical state which depends on electromagnetic fields and exchanges. Certainly this sets a limit to how fast a signal can travel in a solid. In metals, where electrons are shared by the whole lattice, the signal that an electron has been removed travels with the velocity of light through the metal.
But in a lattice with stable configurations of the atoms, connected with electromagnetic springs,an atom can only vibrate in its site location about a center, and transfer the energy vibrationally.
This has been studied using phonons
In physics, a phonon is a collective excitation in a periodic, elastic arrangement of atoms or molecules in condensed matter, like solids and some liquids. Often designated a quasiparticle,1 it represents an excited state in the quantum mechanical quantization of the modes of vibrations of elastic structures of interacting particles.
Also this link is readable on phonons.
A phonon is a quantized mode of vibration occurring in a rigid crystal lattice, such as the atomic lattice of a solid. The study of phonons is an important part of solid state physics, because phonons play an important role in many of the physical properties of solids, such as the thermal conductivity and the electrical conductivity. In particular, the properties of long-wavelength phonons gives rise to sound in solids -- hence the name phonon. In insulating solids, phonons are also the primary mechanism by which heat conduction takes place.
As a rule of thumb , the impulse/kick on a solid object will travel through its lattice at the speed of sound in that solid .
anna v
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I would ask you treat this as a comment, as I don't have the rep to comment, and your question as a homework like question, so I won't answer directly
Look at the crystal structure of any solid object. Imagine the chemical bonds are, in effect, tiny springs. What will happen when you push on one side?
Look at Newton's Cradle motion on YouTube. Also, for liquids and solids, what happens over time, when you push them.
With these sort of questions, I find it best to imagine what is happening in really slowed down motion, like a bullet fired through an apple.