Mass expansion

**sudar_dhoni** · Nov7-09, 05:28 AM

relativity states that as v approaces c mass increases
but my question is that if we are going fast and suddenly mass increases then simultaineously we must slow down and thus we will be back to original state
by this hypothesis i believe that mass expansion is only for minute seconds
AM i right ?

**frankinstein** · Nov7-09, 05:53 AM

Originally Posted by sudar_dhoni

relativity states that as v approaces c mass increases
but my question is that if we are going fast and suddenly mass increases then simultaineously we must slow down and thus we will be back to original state
by this hypothesis i believe that mass expansion is only for minute seconds
AM i right ?

Increasing mass of a body would not slow it down. The mass increase as one approaches the speed of light is in the form of photons. The energy that is applied to accelerate a body as it approaches the speed of light turns into photons rather than pushing the body faster.

Frank

**sudar_dhoni** · Nov7-09, 05:57 AM

Originally Posted by frankinstein

Increasing mass of a body would not slow it down. The mass increase as one approaches the speed of light is in the form of photons. The energy that is applied to accelerate a body as it approaches the speed of light turns into photons rather than pushing the body faster.

Frank

cant understand could u PLZ explain in detail
and also
if possible can u explain how mass is converted to energy and energy is converted to mass
i cant understand how this happens. I want the physical meaning behind this
i console myself by thinking of this example: the food we eat is mass . It is getting digested to give energy so mass is converted to energy. But i am sure that this is wrong

**frankinstein** · Nov7-09, 06:09 AM

Originally Posted by sudar_dhoni

cant understand could u PLZ explain in detail
and also
if possible can u explain how mass is converted to energy and energy is converted to mass
i cant understand how this happens. I want the physical meaning behind this
i console myself by thinking of this example: the food we eat is mass . It is getting digested to give energy so mass is converted to energy. But i am sure that this is wrong

Mass and energy are equivalent by E = mc $LaTeX Code: ^{2}$ . So a body's mass can be increased by adding energy in the form of photons. The conversion of mass to energy and vicesa versa just happens. Its a process of matter that is simply accepted.

**sudar_dhoni** · Nov7-09, 06:28 AM

Originally Posted by frankinstein

Mass and energy are equivalent by E = mc $LaTeX Code: ^{2}$ . So a body's mass can be increased by adding energy in the form of photons. The conversion of mass to energy and vicesa versa just happens. Its a process of matter that is simply accepted.

but photon has zero mass how can addition of photon increase mass also what is the source of photons

**jtbell** · Nov7-09, 08:17 AM

Originally Posted by sudar_dhoni

my question is that if we are going fast and suddenly mass increases then simultaineously we must slow down and thus we will be back to original state

You can increase the speed of an object only by pushing on it with something. The object that is doing the pushing does work on the pushed object, which increases the pushed object's kinetic energy according to the work-energy theorem:

$LaTeX Code: K_{final} = K_{intitial} + W$

This in turn increases the pushed object's total energy

where

is the pushed object's "rest mass," and the "relativistic mass" increases along with the energy according to

.

Both the total energy and momentum of the object vary with speed differently in relativistic mechanics than in classical mechamics:

$LaTeX Code: E = \\frac {m_0 c^2} {\\sqrt {1 - v^2 / c^2}}$

$LaTeX Code: p = \\frac {m_0 v} {\\sqrt {1 - v^2 / c^2}}$

instead of

$LaTeX Code: E = \\frac{1}{2}m_0 v^2$

Originally Posted by frankinstein

The mass increase as one approaches the speed of light is in the form of photons. The energy that is applied to accelerate a body as it approaches the speed of light turns into photons rather than pushing the body faster.

No. Photons are not involved in this, unless of course you are accelerating the object by using photons, as in a solar sail. But here the photons are what is doing the "pushing," and they either disappear or are reflected backwards, depending on whether the sail absorbs or reflects light.

**sudar_dhoni** · Nov7-09, 08:50 AM

i cant understand einsteins mass energy equivalence that how mass can be converted to energy also the concept of rest mass and rest energy
what i thought about mass converted to energy is that

the food we eat is mass . It is getting digested to give energy so mass is converted to energy. But i am sure that this is wrong.
if possible can u also derieve E=mc2

**jtbell** · Nov7-09, 11:27 AM

Originally Posted by sudar_dhoni

the food we eat is mass . It is getting digested to give energy so mass is converted to energy.

Digestion is a series of chemical reactions. In any spontaneous chemical reaction, the sum of the masses of the reactants is greater than the sum of the masses of the products. The difference in mass (which is very tiny) corresponds to the energy released in the reaction.

But i am sure that this is wrong.

Why? (It's dangerous to be sure something is wrong before you fully understand it.

)

**frankinstein** · Nov7-09, 11:43 AM

Originally Posted by jtbell

You can increase the speed of an object only by pushing on it with something. The object that is doing the pushing does work on the pushed object, which increases the pushed object's kinetic energy according to the work-energy theorem:

$LaTeX Code: K_{final} = K_{intitial} + W$

This in turn increases the pushed object's total energy

where is the pushed object's "rest mass," and the "relativistic mass" increases along with the energy according to .

Both the total energy and momentum of the object vary with speed differently in relativistic mechanics than in classical mechamics:

$LaTeX Code: E = \\frac {m_0 c^2} {\\sqrt {1 - v^2 / c^2}}$

$LaTeX Code: p = \\frac {m_0 v} {\\sqrt {1 - v^2 / c^2}}$

instead of

$LaTeX Code: E = \\frac{1}{2}m_0 v^2$

No. Photons are not involved in this, unless of course you are accelerating the object by using photons, as in a solar sail. But here the photons are what is doing the "pushing," and they either disappear or are reflected backwards, depending on whether the sail absorbs or reflects light.

You're right it means that kinetic energy is not realize as linear higher velocity as the object is pushed towards the speed of light.

**Bob S** · Nov7-09, 02:41 PM

Originally Posted by sudar_dhoni

i cant understand einsteins mass energy equivalence that how mass can be converted to energy also the concept of rest mass and rest energy
what i thought about mass converted to energy is that the food we eat is mass . It is getting digested to give energy so mass is converted to energy. But i am sure that this is wrong.
if possible can u also derieve E=mc2

Most of our food energy comes from the oxidation of carbohydrates, such as the monosaccharide C₆H₁₂O₆ (dextrose). The available energy is about 29 eV per molecule. The gram molecular weight is about 180 grams, so very roughly Mc² is 180 AMU or 931 MeV x 180 = 167,000 MeV. So the available chemical energy is about 0.2 parts per billion.
Bob S

**MikeyW** · Nov8-09, 05:57 AM

You are probably thinking that momentum conservation implies if the mass is higher the velocity must be slower. But remember, to increase the velocity in the first place you are adding momentum to the system. So the velocity and mass can both increase simultaneously. Some of the momentum goes to increasing the velocity, and some to increase the mass. The amount of this which is divided between the two depends on the object's speed. If v is close to c, the object will hardly accelerate, but gain a significant amount of mass. If v is near zero, the additional mass will be tiny.

**sudar_dhoni** · Nov8-09, 06:11 AM

Originally Posted by MikeyW

You are probably thinking that momentum conservation implies if the mass is higher the velocity must be slower. But remember, to increase the velocity in the first place you are adding momentum to the system. So the velocity and mass can both increase simultaneously. Some of the momentum goes to increasing the velocity, and some to increase the mass. The amount of this which is divided between the two depends on the object's speed. If v is close to c, the object will hardly accelerate, but gain a significant amount of mass. If v is near zero, the additional mass will be tiny.

ok done but what is the source of that momentum which increases both mass and velocity

**Bob S** · Nov8-09, 05:08 PM

Originally Posted by sudar_dhoni

ok done but what is the source of that momentum which increases both mass and velocity

Fermilab routinely puts about 10¹² protons, and 10¹² anti-protons (in opposite directions) in the Tevatron (a 6280-m circumference synchroton), accelerates them to over 980 GeV total energy using RF cavities, where they can coast all day (synchroton radiation is not a significant problem). The RF cavities are the source of the added momentum. The mass is not increased, but the total energy is.
Bob S