# Does inertia apply to everything in the universe? Even subatomic?

• Quantumgravity

#### Quantumgravity

Does inertia apply to EVERYTHING in the universe? Even subatomic particles? Or is there a certain mass limit where something no longer has the property of inertia?

Mass is inertia.

Does inertia apply to EVERYTHING in the universe? Even subatomic particles? Or is there a certain mass limit where something no longer has the property of inertia?

No, anything that has mass has inertia, as Russ said above. Of course, there are some particles which physicists believe do not have mass. Neutrinos are an example that comes to mind.

Does inertia just mean that it takes energy to move a mass?

Does inertia just mean that it takes energy to move a mass?

"Energy" isn't the right word, but you're moving in the right direction (no pun intended). It's possible for a particle to move without having kinetic energy. Photons, for example, move at a constant vacuum speed c. If an object has inertia, this means that force is required to accelerate it. Newton's Second Law tells us that mass is a resistance to force. So some constant force, when applied to objects of higher mass, will impart less acceleration to them. Thus, you could say that inertia is a measure of how much force is required to accelerate an object at a given rate.

Thanks. That clears it up.
But why don't photons have kinetic energy?

Of course, there are some particles which physicists believe do not have mass. Neutrinos are an example that comes to mind.

Nope, for the past several years it's been widely accepted that neutrinos do have a very small mass (a few eV or less). It's studied via neutrino oscillations.

The only massless particles now, so far as I know, are the photon, the gluons, and the graviton (if it exists).

Nope, for the past several years it's been widely accepted that neutrinos do have a very small mass (a few eV or less). It's studied via neutrino oscillations.

The only massless particles now, so far as I know, are the photon, the gluons, and the graviton (if it exists).

Oops, looks like I missed the memo! Thanks.

But why don't photons have kinetic energy?

I wonder to know why too. I thought photons do have kinetic energy equals to their momentum times the speed of light. Is it correct? Thanks.