High School Can Force Change Mass w/ Constant Velocity?

[hackhard]

can a resultant external force on a body change its mass but keep velocity of its centre of mass constant ? Is it practically possible -
$\vec{F}_{ext}=\vec{v}_{com}\frac{\mathrm{d} M}{\mathrm{d} t}$
where F is nonzero

 

[A.T.]

can a resultant external force on a body change its mass

If the mass is increasing by picking up stuff of different velocity, a force is required to keep velocity constant.

 

[hackhard]

If the mass is increasing by picking up stuff of different velocity, a force is required to keep velocity constant.

no body isn't picking up things. mass increases due to relativistic speed

 

[jbriggs444]

no body isn't picking up things. mass increases due to relativistic speed

Then you would be wise to rewrite the equation since an object's [invariant] mass does not increase due to relativistic speed.

 

[A.T.]

mass increases due to relativistic speed

You said the velocity is constant.

 

[Dale]

no body isn't picking up things. mass increases due to relativistic speed

Relativistic mass is a deprecated concept.

If you want to learn about force in special relativity then you will need to learn about four-vectors.

http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/vec4.html
https://en.m.wikipedia.org/wiki/Four-vector
https://en.m.wikipedia.org/wiki/Four-force

 

[A.T.]

Relativistic mass is a deprecated concept.

Regardless of that, even "relativistic mass" doesn't increase when velocity is constant.

 

[DrStupid]

no body isn't picking up things. mass increases due to relativistic speed

A resultant external force and constant velocity of the center of mass without mass exchange? I'm afraid that's impossible.

 

[hackhard]

I'm afraid that's impossible.

i just needed to know that

 

[pervect]

can a resultant external force on a body change its mass but keep velocity of its centre of mass constant ? Is it practically possible -
$\vec{F}_{ext}=\vec{v}_{com}\frac{\mathrm{d} M}{\mathrm{d} t}$
where F is nonzero

If the net force on a body is nonzero, it must accelerate, therefore the velocity of its center of mass will not be constant if a net force is present.

It is possible to have a pair of opposing forces acting on different parts of a distributed body (which is not a single particle). If this pair of forces is doing net work on the body, the body will gain energy without gaining momentum, which implies that both its relativistic and invariant mass of the body will increase. Note that the energy needs to be stored somewhere, for instance by heating the body (which is due to internal vibrations of its molecules). Usually there is some limit on how much energy a realistic body can absorb in this manner - for instance, if you imagine that the pair of forces is turning a wheel agains some brake drums, the wheel and brakes will heat up, and eventually they'll fail.