Physics

[Guest laguna]

I hate to use this site as "homework help" and i dont have the intention of having you all do my homework for me, however, i am confused about this question we have in physics class. we are supposed to write an essay on the subject of momentum and energy. the question is

 

"How are energy and momentum properties of individual objects? How are they properties of the universe as a whole?"

 

For the first part, i plan on just giving examples of how all types of energy (mechanical, chemical, electomagnetic, thermal, and nuclear) relate to objects, and how momentum relates to objects. however, i'm a bit lost on the universe part.

 

i have kind of an idea for momentum, but overall i'm not really sure on both momentum and energy. if anyone can help me out it would be great.

[VendingMenace]

well...as far as the energy thing goes you might want to talk some about the law that says energy cannot be created or destroyed. Thus, as far as the universe goes, the universe must conatain a certain amount of energy. This amount of energy can neither increase nor decrease. So i think that would be a way to talk about energy as a whole.

 

Now, momentum is slightly harder. YOu might consider talking about how the universe seems to be expanding. Or perhaps how it could be rotating (angulare momentum). Of course the most interesting might be to state that the universe has a total momentum of zero.

 

For the momentum is zero thing, your argument might go as follows. The universe as a whole is not accelerating, as acceleration requires a net force acting on an object. THis force must come from outside the object. Nothing is outside the universe (by definition) thus there cannot be a net force acting on the universe, and we thus know that the universe is not acceperalating. Also, we know that there is a finite amount of mass in the univerese, since mass is related to energy and energy cannot be created nor destroyed. Ok, if there is a finite amount of mass, then we can find the center of mass of the universe. If the universe as a whole cannot be accelerating, then neither can this center of mass. Thus, the center of mass can be our reference frame for our future calculations. If we are using this as our reference frame, then we observe that the center of mass is not moving and we see that the universe has a net momentum of zero.

 

The above paragraph could be wrong, but just off the top of my head, it seemed somewhat interesting.

 

Hopefully that will give you some ideas though

[wolfson]

Very nice comments vending though i would recommend adding equations this one should help:

 

To analyze the dynamics of motion, these equations are used: (calculus is being avoided because it masks the logic.)

 

F = ma v = s/t = at s = ½vt = ½at²

 

Where:

 

F = force v = velocity

m = mass t = time

a = acceleration s = distance (or seconds)

 

 

Consider as an example a 5kg mass accelerated at 10m/s/s for 4 seconds.

 

F = ma = 5(10) = 50 newtons

 

v = at = 10(4) = 40 meters per second

 

s = ½vt = ½(40)(4) = 80 meters

 

(The ½ averages the uniformly changing velocity.)

 

Fs = 50(80) = 4000 newton-meters

 

½mv² = ½(5)(40)² = 4000 joules

[wolfson]

Oh yes and never be affraid to ask school work related questions thats whats this is all about helping people... Good luck

[Kedas]

Just want to add that you also have conservation of angular momentum. (besides linear momentum)

 

If you want the right formules go here:

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html