mass in term of physicist

The supermassive black holes are all that rema...

Image via Wikipedia

Mass does not increase with velocity. Physicists dropped the notion of “relativistic mass” some time ago because it is pedagogically confusing. Mass is an invariant quantity.

the above quote is utterly false, because mass will increase invariantly with more velocity that they achieve.

now I want to talk about physics, i.e mass, in a pedagogically way so that you’ll understand of how these things works.

What do people think of mass? There is “inertial mass” (i.e. a massive object is harder to push than a less massive one) and this is the same as “gravitational mass” (i.e. the earth pulls us down because its massive). We also use some concept of mass in all the equations that you learnt at school, like E=mgh and F=ma and so on. All of these meanings of mass refer to what we now call “relativistic mass”. All of these meanings that I just mention do increase with velocity.

Relativistic mass (Which can also be called ‘energy’) is the only thing that makes sense. If you have two objects with relativistic mass A and relativistic B, then together they will have relativistic mass A+B. This is conservation of energy. Rest mass (what we just call ‘mass’) has no such property, i.e REST MASS is an invariant quantity.

To test if you understood what I said:
*) If strong enough light hits you, will you be pushed backwards? (Light has no rest mass, but it has energy)

the asnwer : Yes, because the movement of the photons grants them a certain amount of mass, regardless of their mass at rest.

*) If you heat a cup of coffee, the particles inside will move faster. Does it become heavier?

the answer : The coffee does become heavier, though you’d never notice it unless you have an insanely sensitive scale.

*) The moon has a huge amount of gravitational potential energy since it’s a frigging heavy rock suspended high above us. And gravitational potential energy is usually described as negative. So .. does this mean there is negative mass here? Does the Earth-moon system have less mass than the mass of the earth + the mass of the moon?

the answer: Yes, by several trillion metric tons! This has been measured and confirmed by bouncing a laser beam off of the moon. The same thing happens with atoms too – the mass of an atom is less than the mass of protons and neutrons and electrons inside of it, because the potential energy is negative.

*) If I have a strong enough beam of light, will I feel myself being pulled towards it due to gravity?

The answer : Yes, light has energy, which has gravitational mass, so we would be pulled towards. In modern language we would say that all energy (including light) causes spacetime to curve. And the curvature tells objects how to move. If you have two strong enough beams of light shining towards each other, you could create a black hole

An apple experiences gravitational fields dire...

Image via Wikipedia

When you accelerate a particle, you give it more energy and thus more inertial mass. It’s harder to push it. If you took a bunch of your particles moving at 99.99999% the speed of light and put them in a box, that box would weigh far more than the rest mass of the particles.

conclusion : mass is just like a spring and it weights ever so slightly more when it’s stretched than when it’s at rest right?

I bet you must missed your pyhsics lesson at your college that you find it’s imperceptible to believe this kind of notion. 🙂


One comment on “mass in term of physicist

  1. […] mass in term of physicist ( […]

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s