
#1
Mar2704, 09:42 AM

P: 51

what happens when there is a mass change in an object?
the mass change is due to its change in its velocity, like when it accelerates from rest to near speed of light, there would be an increase in mass, but how does this happen? would there be a change in the atoms that makes up the object itself??? 



#2
Mar2704, 03:37 PM

Emeritus
Sci Advisor
PF Gold
P: 10,424

The term "mass," as used in modern physics, means "rest mass." This mass does not ever change, no matter what velocity the object has.
 Warren 



#3
Mar2704, 04:15 PM

P: 2,955

http://teachers.web.cern.ch/teachers.../cyclotron.htm I use the term to refer to relativistic mass. So that is what I mean below. Mass increase is a direct result of time dilation and Lorentz contraction. I disagree with chroot's claims that the term "mass" always mean "rest mass" in modern physics. The contrary is an emperical fact. E.g. the texts Relativity: Special, General and Cosmological, Wolfgang Rindler, Oxford Univ., Press, (2001) Cosmological Principles, John A. Peacock, Cambridge University Press, (1999) Understanding Relativity: A Simplified Approach to Einstein's Theories, Leo Sartori, University of California Press, (1996) Basic Relativity, Richard A. Mould, Springer Verlag, (1994) Introducing Einstein's Relativity, Ray D'Inverno, Oxford Univ. Press, (1992) Are perfect counter examples One simply has to look in the relativity literature to see this is not the case. At best there is a majority of particle physicists who use the term that way. In cosmology that does not appear to be the case. In almost all cases authors define the term once and use it as such. For a list of examples from places such as FermiLab, Cern and universities around the globe who use the term "mass" to mean "inertial mass" aka "relativistic mass" please see http://www.geocities.com/physics_wor...istic_mass.htm 



#4
Apr104, 11:38 AM

P: 51

mass change
erm...
ok.. but i still ain't quite sure about the explanation.. my level of studies doesn't offer me the knowledge of time dilation and lorentz contraction, could u explain it to me pls?? 



#5
Apr104, 11:48 AM

P: 1,308





#6
Apr404, 08:04 AM

P: 2,955

alchemist  The concpet of "relativistic mass" is based on things like time and length. Momentum is defined as mass times velocity where velocity is defined as change in distance traveled divided by time required to travel that distance. Since those two things are velocity dependant then this leads to a velocity dependance of mass. 



#7
Apr404, 10:10 AM

P: 51

so what exactly is the mechanism based on? and how does it work?
and if an object reaches the speed of light, it will have an infinite mass?? 



#8
Apr504, 06:55 AM

P: 2,955

To see what time dilation is please see http://www.geocities.com/physics_wor...ight_clock.htm To see what length contraction is please see http://www.geocities.com/physics_wor...ontraction.htm 



#9
Apr504, 11:35 AM

P: 328





#10
Apr504, 12:35 PM

P: 286

In agreeance with DW, I wanted to quote a source by David W. Hogg:




#11
Apr504, 08:29 PM

P: 618

It looks as though you're getting a good tutorial on relativity terminology, but unless I'm mistaken, you're not really getting the answer you're looking for! Try this. Think about a clock radio, and imagine looking at it face on. You hold up a yardstick to measure how long it is. Let's say the 7" mark lines up with the left end of the radio and the 19" mark lines up with the right end of the radio. So you say your clock radio is 12" long. Then you put the clock on a scale. The scale says it weighs about 2.2 lbs. So you say its mass is 1 kilogram. Then you look at what time it is. The clock says 6:00. A little while later, you look at the clock again and it says 6:15. So you say that 15 minutes have past since the last time you checked the time. Then you get another clock radio that's identical to this one. That is, it's 12" long, its mass is 1 kg, and if you synchronize it with the first one at, say, 6:30, they'll still be synchronized at 6:45. Now imagine one clock sliding sideways (parallel to the direction of the length we measured) at some speed v. And imagine that just as the moving clock passes by, both clocks read 7:00. We're going to sit with the stationary clock and measure (somehow) the length and mass of the moving clock and measure what time the moving clock reads when the stationary clock reads 7:15. Here's what Einstein's theory of relativity says we'll get. Our measurement of the length of the moving clock will be less than 1 ft. Our measurement of the mass of the moving clock will be greater than 1 kg. And when the stationary clock reads 7:15, the moving clock won't have gotten to 7:15 yet. It also says this (which seems even more strange). If somebody rides along with the moving clock and makes the same kind of measurements on our stationary clock, they'll measure that IT'S the shorter, heavier and (this one's really strange) slower running one! So where does the increase in mass (or the decrease in length, or the decrease in clock rate) come from? Physics doesn't really answer that kind of question. It only answers questions like this: If I measure something in nature, what result will I get? For example: If I measure the speed of light in empty space, will the result depend on whether the source and/or my measurement system are/is moving. The answer is no. The strange results about mass, length and time that relativity says we'll get are all consequences of this strange answer. 


Register to reply 
Related Discussions  
[SOLVED] change in mass??  Advanced Physics Homework  0  
How do I show that each mass endures an equal and opposite change in momentum...  Introductory Physics Homework  8  
Does any change in energy really cause a change in mass?  Introductory Physics Homework  0  
Does center of mass change if...  Introductory Physics Homework  2  
Does mass of an object truly change with velocity(I found an very interesting text.)  General Physics  1 