# Do the electrons have inertial mass?

1. Dec 14, 2011

### FranciscoAlm

Hello there!
According to quantum physics, do the electrons have inertial mass? I read somewhere electrons were an amount of energy, with no mass at all. I think I'm confused about the concept of "mass" since I know two, the one they taught me at school, which I'm considering as inertial mass and the one on relativity that is related to energy, right?
(Sorry if I'm saying something stupid, I'm sixteen and I actually am new here and the knowledge I have about quantum physics and so on is due to my own research.)
Anyway, thanks for the help.

2. Dec 14, 2011

### e.bar.goum

Hi, welcome to PF!

Isn't quite true, perhaps you're thinking of a photon? Electrons are a massive particle, with a rest mass of about 9.10938×10^-31 kg

3. Dec 14, 2011

### joris_pixie

Yes, they have inertial mass :)

Often is said they have no mass cause it's so small compared with neutrons and protons.

Relative mass is

mr = mi / $\sqrt{1 - v²/c²}$

with v = velocity, c = light of speed
As you see for low speed this is the kinda the same as inertial mass :)

4. Dec 15, 2011

### vanhees71

It cannot be stressed enough that the quantity you give as "mass" is not mass in the modern sense (if you assume a scientific achievement as "modern" although it has been obtained over 100 years ago) but Energy (divided by $c^2$).

In relativistic physics mass means the invariant mass of an object, i.e., a scalar quantity while energy is the time component of the energy-momentum four-vector.

5. Dec 15, 2011

### FranciscoAlm

Got it! Thank you all :)
I spent some time researching the difference between the two masses and with what you said here and with what I've read, I think I understood it.
I really meant electron e.bar.goum , but since you spoke of photons, I'll do some more research about them just for the fun of learning :)