pure energy.

[dstebbins]

Things like light, sound, and electromagnetic radiation are considered pure energy, meaning they have no mass. Well, the unit of energy, the Joule, is expressed in base units as kg*m^2/s^2. Well, kilograms is a unit of mass, right? So by that logic, since there is mass in the unit, shouldn't there be mass in the energy? According to the laws of mathematics, you can't have a unit of something without it being present. If energy has zero mass, then any number times zero is zero, so an object with no mass, such as light, should thus have no energy, yet it does.

 

I've never been right on this site before, so the chances that I'm right this time are slim, so where am I going wrong?

[ErlyRisa]

no I say you are right!!

 

--but

 

E= m c^2 !

 

-- E = material pattern X velocity^2... where space => by light.

 

light is the ether.... the most rudimentary entanglement of information.

 

therfore E=information = 0011

[Spyman]

How do you measure the difference in energy between a relaxed and stretched rubber band or spring ?

 

Mass is the property of a physical object that quantifies the amount of matter and energy it is equivalent to.

 

In classical mechanics, there are three types of mass or properties called mass:

Inertial mass is a measure of an object's resistance to changing its state of motion when a force is applied. An object with small inertial mass changes its motion more readily, and an object with large inertial mass does so less readily.

Passive gravitational mass is a measure of the strength of an object's interaction with the gravitational field. Within the same gravitational field, an object with a smaller passive gravitational mass experiences a smaller force than an object with a larger passive gravitational mass. (This force is called the weight of the object. In informal usage, the word "weight" is often used synonymously(confused with) with "mass", because the strength of the gravitational field is roughly constant everywhere on the surface of the Earth. In physics, the two terms are distinct: an object will have a larger weight if it is placed in a stronger gravitational field, but its passive gravitational mass remains unchanged.)

Active gravitational mass is a measure of the strength of the gravitational field due to a particular object. For example, the gravitational field that one experiences on the Moon is weaker than that of the Earth because the Moon has less active gravitational mass.

http://en.wikipedia.org/wiki/Mass

 

 

With light you need to consider the relativistic mass...

 

a photon's momentum is a function of its energy; it is not analogous to the momentum in Newtonian mechanics.

 

E=mc² is only valid when the object is at rest. If the object is in motion, we have E²=(mc²)²+(pc)²

http://en.wikipedia.org/wiki/Mass_in_special_relativity

[ErlyRisa]

could it be that E as in a spring =

 

E = d(change from relaxed origin)c^2 ?

 

or

 

= m(v1-v2)^2

[swansont]

According to the laws of mathematics, you can't have a unit of something without it being present.

 

When did they pass that law?

 

Torque is N-m, same as energy, as 1 J = 1 N-m. But torque and energy are not the same. There is more to physics than unit analysis.

[dstebbins]

Okay, can everyone PLEASE slow down?! How can you expect me to read four posts at one time and still be able to comprehend these things as if it were just a single lesson? There's a REASON a college physics class is spread out over an entire semester, you know.

 

Now, let's start over, and PLEASE speak in laymen's terms: What am I doing wrong in this logic?

[insane_alien]

Okay, can everyone PLEASE slow down?! How can you expect me to read four posts at one time and still be able to comprehend these things as if it were just a single lesson? There's a REASON a college physics class is spread out over an entire semester, you know.

 

well, this is a forum. you can read over the posts. go have a cup of tea and think about the replies you got. even go on holiday for a month and mull them over and you can still come back and reply. you can take as long as you want to try and make sense of them. we'll still be here.

 

i think you can ignore erlyrisa's posts as they are more than a little inaccurate.

 

basically, what is being said is that the units aren't everything to a value in physics. a better way of understanding it is to begin with the simple formulae and build it up to the unit formula.

 

so we'll start with Energy= Force * Distance.

 

this has units of N-m (obviously) nice and simple.

distance is a measure of a dimension so we can't break that down any further. so lets look at force.

 

Force= mass * acceleration (kg-m/s^2)

 

so 1 N is the force required for 1 kg to accelerate at 1 m/s^2

 

from this we can get the units of a joule. a kg-m^2/s^2 . this does look kind of horrible i'll admit that.

 

but, all it is, is the energy required to accelerate 1 kg at 1 m/s^2 over a distance of one meter.

 

now, the energy doesn't have to be accelerating anything over any distance to exist. and that energy itself doesn't have mass(well, it does a bit but it is negligble for a basic understanding). so we can see that the mass unit comes into play when you are quantifying the energy. it is a measure of how much work it can do.

 

so a photon can exist without mass because it is merely energy. not the object the energy is acting upon.

 

or something like that. i'm sure swansont will correct any glaring errors. i hope it was simple enough for you and i hope that you'll take a bit of time to think about it if you don't get it right away. just remember that there is no rush to reply here. it is not IRC.

 

<edit>woah, just realised how much i wrote. seemed a lot shorter.

[swansont]

so we can see that the mass unit comes into play when you are quantifying the energy. it is a measure of how much work it can do.

 

And that's the important part.

 

You can move mass around with energy, but you don't have to.

[dstebbins]

So let me try and get this straight: The kilograms noted in the unit of energy is talking about the mass that the energy has the potential to act upon; THAT'S why it's in the unit. Is that it?

[insane_alien]

umm pretty much. its one of the variables it can act upon. its not a fixed unit or anything. its in relation to the other variables as well.

[swansont]

You can also create mass from other forms of energy. [math]E=mc^2[/math] (actually [math]E^2 = p^2c^2 + m^2c^4[/math])

[dstebbins]

You can also create mass from other forms of energy. [math]E=mc^2[/math] (actually [math]E^2 = p^2c^2 + m^2c^4[/math])

 

which just furthers my confusion. If we can make mass from energy and energy from mass, shouldn't they have some kind of connection in the form department? At least a distant one?

[Klaynos]

which just furthers my confusion. If we can make mass from energy and energy from mass, shouldn't they have some kind of connection in the form department? At least a distant one?

 

They are connected with the equation that Swansont posted.

 

http://en.wikipedia.org/wiki/Mass-energy_equivalence

 

Gives an okish description.