Freethought & Rationalism Archive

Baloo · 03-08-2002, 12:10 PM

Let's just all calm down for a second - and start from scratch. Everyone take a seat, as we embark on Physics 101**.

Let's establish the meanings of some very basic terminology. Length (which we will measure in meters) is a measure of distance. We will use seconds as our basic unit of time. Velocity is the measure of how quickly an object moves from one place to anoth, and is calculated as Length divided by Time. For example, if an object travels 10 meters in 1 second, we can say its average velocity was 10 meters/second. Acceleration is the rate at which velocity changes (it tells us how fast something is "speeding up" or "slowing down"), and is calculated as velocity divided by time. For example, if an object is not moving (has a velocity of 0 meters/second), but 1 second later, it has reached a velocity of 10 meters/second, we can say its average acceleration is 10 (meters/second) per second.

Real quick, let's establish some short hand notation. I will denot meters as 'm' and seconds as 's'. Units of velocity are therefore m/s (meters per second), and acceleration is m/s^2 (meters per (second squared)).

Mass (NOT weight) is simply the measure of matter in an object. It is commonly represented in kilograms (shorthand = kg). Now we get into the fun stuff. You are probably familiar with the rule: Any object at rest will remain at rest until acted on by a force. What does this mean in terms we've established so far? It basically says that an object with a velocity of 0 m/s will retain a velocity of 0 m/s until a "Force" acts on it. To change an objects velocity, we know we have to accelerate it. Force is the measure of "what it takes" to accelerate an object. In a nutshell, if you take the mass of an object and multiply it by the desired acceleration, you obtain the "force" necessary. For example, if we have a 10 kg object, and wish to accelerate it at 10 m/s^2, we require a force of (10 kg) * (10 m/s^2) = 100 kg * m/s^2.

Ouch, these shorthand notations are getting messy. Well, physicists have demonstrated conclusively that they can be just a lazy as computer scientists; hence we get the term "Newton". A Newton (shorthand = N) is the basic metric representation of Force. 1 Newton is equal to 1 kg * m/s^2. The force in the example above thus changes from 100 kg*m/s^2 to simply 100 N (read 100 Newtons). Perhaps the most common force we know of is the force of gravity. At the earth's surface, if you drop a 10 kg ball with an initial velocity of 0 m/s, you will see it's velocity change, and it will fall to the ground. In fact, it will accelerate at a rate of about 9.8 m/s^2. Thus, the force of gravity on this 10 kg ball is (10 kg) * (9.8 m/s^2), or 98 Newtons (98 N). On a side note, weight (NOT mass) is a measure of force. If I weigh 240 pounds, what I mean is that at the earth's surface, the force of gravity on my body is 240 pounds (this unit can be directly converted to 1067 Newtons - divide 1067 kg*m/s^2 by the gravitational acceration rate of 9.8 m/s^2, and we get my mass of 109 kg).

And now, finally, we get into the really good stuff. Energy. How the hell does Energy fit into the above terms? Potential Energy is defined as the force applied to an object multiplied by the distance the object travles while the force is applied. Since it is measured in (Force) times (Distance), it's units are Newtons * Meters (shorthand N*m, or (kg*m/s^2)*m, or kg*m^2/s^2). Enter lazy physicist, for whom N*m is just too time-consuming to write, and we get the new term Joule. The Joule (shorthand J) is therefore the basic measure of energy. A quick example: how much energy is in a 10 kg brick that has been lifted 10 meters above the ground? Well, the mass is 10 kg, thus the force due to gravity is 98 Newtons. Multiply this by the distance it has been lifted, and you get a Potential Energy of 980 Joules (or 980 kg*m^2/s^2).

Next, the fun continues with Kinetic Energy. Kinetic energy is defined as 1/2 of the mass of an object multiplied by the square of it's velocity. That is, KE = (1/2)(mass)(velocity^2).

Huh? Okay, let's look at our 10 kg brick. It is hovering 10 meters in the air, with a potential energy of 980 Joules. Using a little math, we can show that if we dropped the brick, it would accelerate at 9.8 m/s^2, reaching the ground with a final velocity of 14 m/s {velocity = square root of (2 * acceleration * distance of acceleration) = sqrt(2*9.8*10) m/s = 14 m/s}.

Plugging 14 m/s into the formula for kinetic energy, we see that the 10 kg object traveling at 14 m/s has (1/2) * (10 kg) * (14 m/s)^2 = 980 Joules. The kinetic energy, you see, is exactly equal to the original potential energy. They even have the same units.

And, now, the ultimate. What is PRESSURE? Easy. Pressure (as I stated in my original post) is the measure of force against a surface. If 100 Newtons are pressing against a 1 meter x 1 meter surface, the Pressure is 100 N/m^2. In lazy physicist terms, a N/m^2 is call a Pascal (shorthand Pa), and so 100 N/m^2 would be called 100 Pa. The atmosphere, for another example, has a pressure of about 1 hundred thousand (100,000) Pa, which means for every square meter of ground, it exerts a force of 100,000 N/m^2.

And here enters the confusion. How is pressure related to energy? I mean, one is force times distance (N*m), the other is force divided by distance squared (N/m^2). It's quite simple, really. The Potential Energy of pressure is the measure of the pressure of a material multiplied by the volume of the material. To see this in practice, imagine a 10 kg canister at the bottome of a vertical tube (for simplicity, assume the tube is a vaccuum). Now, let's say we have an oxygen tank, with 1 cubic meter of oxygen, at a pressure of 980 Pa. The amount of potential energy of the oxygen tank is thus 100 Pa * 1 m^3 = 980 Joules. If we hook the tank up to the tube, and blow all of the air from the tank into the tube, how high can it blow the 10 kg canister? If all of the potential energy in the tube were used to lift the canister into the air, the canister would be lifted 10 meters into the air, giving the canister a potential energy of 980 Joules.

Now, in this context, Corwin is absolutely right when he says a pressurized system has energy. However, the energy is a form of Potential Energy, and not thermal energy. A pressurized system can only lose or gain Potential Energy with a change in pressure or volume. So, Corwin, even though you are correct in saying that there is Potential Energy at the core of the earth due to pressure, you are 100% incorrect in suggesting that that Potential Energy is being converted to heat, because this energy is only released with a CHANGE in pressure...

One final point. There is a very, VERY key point of basic physics: FOR TWO MEASUREMENTS TO BE COMPARED, THEY MUST HAVE THE SAME UNITS . You cannot say whether 2 Newtons is bigger or smaller than 1 meter. You cannot say that 3 Joules is faster or slower than 5 meters/second. You cannot say that 5 Newtons of force is hiegher or lower than 10 Pascals. AND YOU CANNOT, UNDER ANY CIRCUMSTANCES, COMPARE PRESSURE TO ENERGY. They are not the same thing. End of story. End of class.

**In this classroom, there is no time-dilation or quantum effects, and for simplicity sake distance and displacement mean the same thing; velocity and speed mean the same thing.

[ March 08, 2002: Message edited by: Baloo ]

Corwin · 03-08-2002, 12:11 PM

Quote:

Originally posted by Deimos:
This is getting quite funny.

Corwin, put up or shut up. If you can lay out the sequence of calculations that show how a mechanical pressure distribution leads to the heating of an object then go for it. The constraint on this is that the objects dimensions are unchanged by the application of the pressure. Otherwise quit acting like a moron

.

Here, I'll give you something to chew on :

Tell us how much this column would be heated by the application of the pressure.

And to answer this I'd need more information, like exactly what the column is made of, (yes it does make a difference) and several formulae that I don't happen to have. Again, we're talking conceptual theory here, not math. (That's a different part of the process.)

tronvillain · 03-08-2002, 12:11 PM

Corwin:

Quote:

So possibly you could explain to poor little crazy deluded psudeoscientific me how force is NOT energy? Or is all you have 'noitisn'tnoitisn'tnoitisn't?'

Force is not energy, by definition. The units of force are newtons, and the units of energy and work are joules. See? Not the same. If they were the same, they'd have the same units.

From <a href="http://www.mcm.edu/~christej/dictionary/framedict.html" target="_blank">Tensen Productions</a>:

Quote:

energy: Technically defined as the "ability to do work", this concept is traditionally thought of as difficult to grasp initially. The concept has to do with the colloquial idea of effort (see work). Since it takes some effort to move an object, we say a moving object has kinetic energy. Similarly, it takes some effort to lift an object; we would like to define an energy to associate with lifting or dropping an object --- this is the potential energy. The "ability to do work," then is our ability to get energy out of an object. An object loses energy by giving it to other objects. If a moving truck hits a parked car, the car gains some energy and the truck loses some; the truck has "done some work" on the car. (See work) (Energy is expressed in units of joule which were named for James Prescott Joule.)
Since it is also possible to have work done by objects which are warm, heat can be said to be a form of energy. In fact, Einstein's famous equation, E=mc2, expresses that mass can also be considered a form of energy, although it is less obvious that this is the case.

force: That which causes matter to change its velocity. Studied by many people, including Galileo, it was not until Newton formulated his three laws that the concept of force was placed on solid mathematical footing. (See Newton's Laws --- Newton used the word "action" to describe what we now call "force"; we now have a different meaning for the word action.) While forces may be due to an explicit "push" or a collision, they may also be due to the interaction between objects with some property which can in general be called charge. The latter type of force is referred to as a fundamental force or more generally as an interaction between charges.

I'm sorry, but you're wrong. Get over it.

[ March 08, 2002: Message edited by: tronvillain ]

tronvillain · 03-08-2002, 12:14 PM

Deimos:

Quote:

Tell us how much this column would be heated by the application of the pressure.

Actually, that's not what we want him to tell us. We want to know how constant pressure produces heat, not how applying pressure to a system will heat it.

Corwin · 03-08-2002, 12:19 PM

Bal... thanks for the definitions. Now...

For every action, there is an equal and opposite reaction. (Classical physics, I know... but still valid in this context.) Now... what we have at the center of the earth is a MASSIVE compressive force.

This is, in fact, the kind of force people are looking at using to make thermonukes that don't require a fission nuke to set them off.

This pressure is constant. Which means that in this system what you have is a constant application of force. Again.... it all has to go somewhere.

We also have to clarify my position.... (as it's been misinterpeted by people who are biased against my positions from other posts....) I'm not claiming this is the SOLE cause of the temperature at the earth's core, and never have. But it does have some effect.

It never ceases to amaze me how people will take my fairly moderate position and warp it to seem like I'm some blissed out wacko. Oh well.

Corwin · 03-08-2002, 12:20 PM

And 'causing matter to change it's velocity?'

Gee.... sounds like WORK to me.

tronvillain · 03-08-2002, 12:22 PM

Baloo:

Quote:

Now, in this context, Corwin is absolutely right when he says a pressurized system has energy. However, the energy is a form of Potential Energy, and not thermal energy. A pressurized system can only lose or gain Potential Energy with a change in pressure. So, Corwin, even though you are correct in saying that there is Potential Energy at the core of the earth due to pressure, you are 100% incorrect in suggesting that that Potential Energy is being converted to heat, because this energy is only released with a CHANGE in pressure...

I pointed this out on the second page: "It's potential energy. Not only are humans not using it for anything, it's not doing anything. In the case of the Earth, it is not heating the Earth's core."

Anyway, it's nice to get some other contribution to the thread. Thanks Baloo.

Corwin · 03-08-2002, 12:25 PM

Fine tron.... so maybe you can explain where all that energy.... POTENTIAL OR OTHERWISE... is going?

Absorbed by the other matter around it? Fine, so either you're going to shatter the planet, or increase its temperature. Take your pick. Energy doesn't just sit there, potential or otherwise. There's always some effect. (Whether it's enough for us to notice or not is irrelevant.)

tronvillain · 03-08-2002, 12:29 PM

Corwin:

Quote:

And 'causing matter to change it's velocity?'

Gee.... sounds like WORK to me.

It may sound like it to you, but it's not, at least not if you're using the normal scientific definition of work.

[ March 08, 2002: Message edited by: tronvillain ]

Corwin · 03-08-2002, 12:33 PM

From <a href="http://physics.about.com/library/dict/bldefwork.htm" target="_blank">http://physics.about.com/library/dict/bldefwork.htm</a>

Quote:

Definition: The work done by a force acting on a body is the product of the force and the distance moved by its point of application in the direction of the force. If a force F acts in such a way that the displacement, s, is in a direction that makes an angle q with the direction of the force, the work done is given by: W = F s cos q or in vector notation, W = F�s. Work is the scalar or dot product of the force and displacement vectors.

Unit: joules, 1 J = 1 kg2�m2/s2
<http://images.about.com/all/bullets/dot_clea.gif>

Your site doesn't even define work. Gee....

03-08-2002, 12:10 PM	#71
Baloo Regular Member Join Date: Jun 2000 Location: St. Louis, MO Posts: 417	Let's just all calm down for a second - and start from scratch. Everyone take a seat, as we embark on Physics 101. Let's establish the meanings of some very basic terminology. Length (which we will measure in meters) is a measure of distance. We will use seconds as our basic unit of time. Velocity is the measure of how quickly an object moves from one place to anoth, and is calculated as Length divided by Time. For example, if an object travels 10 meters in 1 second, we can say its average velocity was 10 meters/second. Acceleration is the rate at which velocity changes (it tells us how fast something is "speeding up" or "slowing down"), and is calculated as velocity divided by time. For example, if an object is not moving (has a velocity of 0 meters/second), but 1 second later, it has reached a velocity of 10 meters/second, we can say its average acceleration is 10 (meters/second) per second. Real quick, let's establish some short hand notation. I will denot meters as 'm' and seconds as 's'. Units of velocity are therefore m/s (meters per second), and acceleration is m/s^2 (meters per (second squared)). Mass (NOT weight) is simply the measure of matter in an object. It is commonly represented in kilograms (shorthand = kg). Now we get into the fun stuff. You are probably familiar with the rule: Any object at rest will remain at rest until acted on by a force. What does this mean in terms we've established so far? It basically says that an object with a velocity of 0 m/s will retain a velocity of 0 m/s until a "Force*" acts on it. To change an objects velocity, we know we have to accelerate it. Force is the measure of "what it takes" to accelerate an object. In a nutshell, if you take the mass of an object and multiply it by the desired acceleration, you obtain the "force" necessary. For example, if we have a 10 kg object, and wish to accelerate it at 10 m/s^2, we require a force of (10 kg) (10 m/s^2) = 100 kg * m/s^2. Ouch, these shorthand notations are getting messy. Well, physicists have demonstrated conclusively that they can be just a lazy as computer scientists; hence we get the term "Newton". A Newton (shorthand = N) is the basic metric representation of Force. 1 Newton is equal to 1 kg * m/s^2. The force in the example above thus changes from 100 kgm/s^2 to simply 100 N (read 100 Newtons). Perhaps the most common force we know of is the force of gravity. At the earth's surface, if you drop a 10 kg ball with an initial velocity of 0 m/s, you will see it's velocity change, and it will fall to the ground. In fact, it will accelerate at a rate of about 9.8 m/s^2. Thus, the force of gravity on this 10 kg ball is (10 kg) (9.8 m/s^2), or 98 Newtons (98 N). On a side note, weight (NOT mass) is a measure of force. If I weigh 240 pounds, what I mean is that at the earth's surface, the force of gravity on my body is 240 pounds (this unit can be directly converted to 1067 Newtons - divide 1067 kgm/s^2 by the gravitational acceration rate of 9.8 m/s^2, and we get my mass of 109 kg). And now, finally, we get into the really good stuff. Energy. How the hell does Energy fit into the above terms? Potential Energy* is defined as the force applied to an object multiplied by the distance the object travles while the force is applied. Since it is measured in (Force) times (Distance), it's units are Newtons * Meters (shorthand Nm, or (kgm/s^2)m, or kgm^2/s^2). Enter lazy physicist, for whom Nm is just too time-consuming to write, and we get the new term Joule. The Joule (shorthand J) is therefore the basic measure of energy. A quick example: how much energy is in a 10 kg brick that has been lifted 10 meters above the ground? Well, the mass is 10 kg, thus the force due to gravity is 98 Newtons. Multiply this by the distance it has been lifted, and you get a Potential Energy of 980 Joules (or 980 kgm^2/s^2). Next, the fun continues with Kinetic Energy. Kinetic energy is defined as 1/2 of the mass of an object multiplied by the square of it's velocity. That is, KE = (1/2)(mass)(velocity^2). Huh? Okay, let's look at our 10 kg brick. It is hovering 10 meters in the air, with a potential energy of 980 Joules. Using a little math, we can show that if we dropped the brick, it would accelerate at 9.8 m/s^2, reaching the ground with a final velocity of 14 m/s {velocity = square root of (2 * acceleration * distance of acceleration) = sqrt(29.810) m/s = 14 m/s}. Plugging 14 m/s into the formula for kinetic energy, we see that the 10 kg object traveling at 14 m/s has (1/2) * (10 kg) * (14 m/s)^2 = 980 Joules. The kinetic energy, you see, is exactly equal to the original potential energy. They even have the same units. And, now, the ultimate. What is PRESSURE? Easy. Pressure (as I stated in my original post) is the measure of force against a surface. If 100 Newtons are pressing against a 1 meter x 1 meter surface, the Pressure is 100 N/m^2. In lazy physicist terms, a N/m^2 is call a Pascal (shorthand Pa), and so 100 N/m^2 would be called 100 Pa. The atmosphere, for another example, has a pressure of about 1 hundred thousand (100,000) Pa, which means for every square meter of ground, it exerts a force of 100,000 N/m^2. And here enters the confusion. How is pressure related to energy? I mean, one is force times distance (Nm), the other is force divided* by distance squared (N/m^2). It's quite simple, really. The Potential Energy of pressure is the measure of the pressure of a material multiplied by the volume of the material. To see this in practice, imagine a 10 kg canister at the bottome of a vertical tube (for simplicity, assume the tube is a vaccuum). Now, let's say we have an oxygen tank, with 1 cubic meter of oxygen, at a pressure of 980 Pa. The amount of potential energy of the oxygen tank is thus 100 Pa * 1 m^3 = 980 Joules. If we hook the tank up to the tube, and blow all of the air from the tank into the tube, how high can it blow the 10 kg canister? If all of the potential energy in the tube were used to lift the canister into the air, the canister would be lifted 10 meters into the air, giving the canister a potential energy of 980 Joules. Now, in this context, Corwin is absolutely right when he says a pressurized system has energy. However, the energy is a form of Potential Energy, and not thermal energy. A pressurized system can only lose or gain Potential Energy with a change in pressure or volume. So, Corwin, even though you are correct in saying that there is Potential Energy at the core of the earth due to pressure, you are 100% incorrect in suggesting that that Potential Energy is being converted to heat, because this energy is only released with a CHANGE in pressure... One final point. There is a very, VERY key point of basic physics: FOR TWO MEASUREMENTS TO BE COMPARED, THEY MUST HAVE THE SAME UNITS . You cannot say whether 2 Newtons is bigger or smaller than 1 meter. You cannot say that 3 Joules is faster or slower than 5 meters/second. You cannot say that 5 Newtons of force is hiegher or lower than 10 Pascals. AND YOU CANNOT, UNDER ANY CIRCUMSTANCES, COMPARE PRESSURE TO ENERGY. They are not the same thing. End of story. End of class. **In this classroom, there is no time-dilation or quantum effects, and for simplicity sake distance and displacement mean the same thing; velocity and speed mean the same thing. [ March 08, 2002: Message edited by: Baloo ]</p>

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03-08-2002, 12:19 PM	#75
Corwin Veteran Member Join Date: Jan 2002 Posts: 4,369	Bal... thanks for the definitions. Now... For every action, there is an equal and opposite reaction. (Classical physics, I know... but still valid in this context.) Now... what we have at the center of the earth is a MASSIVE compressive force. This is, in fact, the kind of force people are looking at using to make thermonukes that don't require a fission nuke to set them off. This pressure is constant. Which means that in this system what you have is a constant application of force. Again.... it all has to go somewhere. We also have to clarify my position.... (as it's been misinterpeted by people who are biased against my positions from other posts....) I'm not claiming this is the SOLE cause of the temperature at the earth's core, and never have. But it does have some effect. It never ceases to amaze me how people will take my fairly moderate position and warp it to seem like I'm some blissed out wacko. Oh well.

03-08-2002, 12:20 PM	#76
Corwin Veteran Member Join Date: Jan 2002 Posts: 4,369	And 'causing matter to change it's velocity?' Gee.... sounds like WORK to me.

03-08-2002, 12:25 PM	#78
Corwin Veteran Member Join Date: Jan 2002 Posts: 4,369	Fine tron.... so maybe you can explain where all that energy.... POTENTIAL OR OTHERWISE... is going? Absorbed by the other matter around it? Fine, so either you're going to shatter the planet, or increase its temperature. Take your pick. Energy doesn't just sit there, potential or otherwise. There's always some effect. (Whether it's enough for us to notice or not is irrelevant.)

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