What is relativistic mass and rest mass

[Rico L]

what is "relativistic mass" and "rest mass"..

as far as i know the rest mass is the mass which measured by an observer who is at rest relative to the object (please correct me if this is not right), if this is right... what if when the object is traveling at the exactly same velocity of the observer.. does "rest mass" also applies to this situation?

relativistic mass is the mass of an object measured by an observer who is moving relative to the object or the mass of an object moving relative to an observer who is measuring the mass entitled to regard himself as stationary. i mean if this is right, in which way, how can the mass be measured if the object is moving.. ?

i am so confused...

thanks

 

[mgb_phys]

With small particles where their energy when they are moving is larger than their rest mass we can measure their relativistic mass.

So an electron has a rest mass of 511Kev (we even measure rest mass in units of energy) at high speed we can determine it's mass by the momentum effects when it hits something.

But yes it's diffcult to put an electron moving near the speed of light on a set of scales!

 

[LostConjugate]

what if when the object is traveling at the exactly same velocity of the observer..

This is the same thing as being at rest relative to the observer.

relativistic mass is the mass of an object measured by an observer who is moving relative to the object or the mass of an object moving relative to an observer who is measuring the mass entitled to regard himself as stationary. i mean if this is right, in which way, how can the mass be measured if the object is moving.. ?

i am so confused...

thanks

It could be measured by applying a small perpendicular force to the object. As it travels by you can measuring by how much it's path changes direction. mass resists force.

It can also be calculated because 2E/v^2 = m so the connections between Velocity and Mass are clear.

 

[Janus]

as far as i know the rest mass is the mass which measured by an observer who is at rest relative to the object (please correct me if this is not right), if this is right... what if when the object is traveling at the exactly same velocity of the observer.. does "rest mass" also applies to this situation?

Yes, all that counts is the relative velocity between the object and measurer. Either one's relative motion relative to any other reference doesn't matter.

relativistic mass is the mass of an object measured by an observer who is moving relative to the object or the mass of an object moving relative to an observer who is measuring the mass entitled to regard himself as stationary. i mean if this is right, in which way, how can the mass be measured if the object is moving.. ?

By measuring how much effort it takes to change the velocity of the object.

 

[Rico L]

thanks a lot guys ! :)

 

[starthaus]

It could be measured by applying a small perpendicular force to the object. As it travels by you can measuring by how much it's path changes direction. mass resists force.

Yes, the rest mass can be inferred from deflection experiments :

$$m_0=\frac{qB}{\omega \gamma(v_0)}$$

or$$m_0=\frac{qBr}{v_0 \gamma(v_0)}$$

where:

B=magnetic induction
q=particle charge
r=radius of the circular trajectory
v_0 = initial speed of the particle when injected in the cyclotron
$$\omega=2 \pi/T$$
T=period of particle revolution