Something to think about instead of working

[szh]

H, Toki, I apologise for getting pedantic here and I hate to make this thread any more geeky than I already have, but let me just cover two final points (I jumped in earlier only to correct your misconceptions about Newtonian mechanics and its relationship to light!) and then I will shut up. (And the crowd goes Yay!)

First, "zero mass" means ZERO mass - not SMALL mass, or MINUTE mass, or TINY mass. It is true ZERO mass - to any measure that man has been able to do to date! Hence the ability for photons to move at "light speed" - instantly, no acceleration, no infinite mass or energy required, no Star Trek warp theories needed - without any special problems . Photon zero mass is a cornerstone of Einstein's Special Theory of Relativity. Newton's F=ma does not apply to photons.

Second, Newtonian mechanics do not really mean much any more - they only apply in the most basic of gross (i.e., on a "large-scale", low resolution) measurements. But, quantum mechanics and both of Einstein's relativity theories outmoded Newtonian mechanics a long time back!

Newton was a giant in his time, and a lot of early physics work rested on his shoulders. Newtonian mechanics is still taught in schools and colleges so people have a basic foundation to build on. And because from a large-scale observation perspective (people do not measure in nanometers, for example, or estimate the speed of light based on our eyesight !), his laws appear to apply for all practical day-to-day purposes. Whether you are playing billiards or accelerating a car or whatever ... ! Fine and dandy! But not modern physics.

Again, sorry to wax too geekily here!

Z

[reggiegsd]

Haven't you heard? Geekiness is cool now.

Try this one. If light is emmitted from an object that is traveling at half the speed of light, what speed does the light appear to be traveling to an observer that is stationary?

This should be good for a week.

[DAEDALUS]

Photons do not "accelerate" - light always travels at a maximum velocity for the medium it is in.

Z

[toki]

No worries about the geekness. I'm with ya. haha. But zero mass just doesn't compute for me. It's theoritical only...like a plane. 0 height and 10 width and 10 length. How can something have 0 height? If if doesnt have a height...it can't exist. Even a single atom has a height, so I don't see how it could exist. Everything has to have a weight to exist. Just because we can't measure it doesn't mean it's not there.

[szh]

Early romans had a problem with zero, too! That is why there is no symbol for 0 in roman numbers. It was the Arabs who introduced the concept of "zero" to western countries and they got it from Indian mathematicians many centuries ago.

Z

[szh]

Try this one. If light is emitted from an object that is traveling at half the speed of light, what speed does the light appear to be traveling to an observer that is stationary?

This should be good for a week.

Daedalus got it right! Didn't take a week ...

Z

[szh]

No worries about the geekness. I'm with ya. haha. But zero mass just doesn't compute for me. It's theoritical only...like a plane. 0 height and 10 width and 10 length. How can something have 0 height? If if doesnt have a height...it can't exist. Even a single atom has a height, so I don't see how it could exist. Everything has to have a weight to exist. Just because we can't measure it doesn't mean it's not there.

Light (and photons) does not obey the Newtonian principles you are expounding here!

If you wanna know more, you are going to have to dive into it a bit with some text books. Look at some of the URL's from my first post above - especially the first one.

Z

[Onizuka]

farts smell like poopy

[szh]

Daedalus got it right! Didn't take a week ...

And here is a link that explains it very well:

http://csep10.phys.utk.edu/gui....html

[szh]

And if you think that this discussion was not mind-bending enough, it is believed that the speed of light has been dropping since the creation of the universe:

http://www.ldolphin.org/setterfield/redshift.html

Here is another question for you all: how much energy is there in a cubic centimeter of total vacuum?

Z

[szh]

How to find the speed of light (approximately) using marshmallows:

http://www.physics.umd.edu/rip...l.htm

And if this above doesn't get you and your kids (if you have any) interested in physics, nothing will!

Z

[szh]

Here is how to slow down light to the speed of a Q45 (sort of):

http://www.nature.com/nsu/030324/030324-4.html

Z

[szh]

You too can stop light:

http://www.nature.com/nsu/010125/010125-3.html

Z

[szh]

What is the term used for the third derivative of position?

Original by Philip Gibbs September 1996.

It is well known that the first derivative of position (symbol x) with respect to time is velocity (symbol v) and the second is acceleration (symbol a). It is a little less well known that the third derivative, i.e. the rate of change of acceleration, is technically known as jerk (symbol j). Jerk is a vector but may also be used loosely as a scalar quantity because there is not a separate term for the magnitude of jerk analogous to speed for magnitude of velocity.

In the UK jolt has sometimes been used instead of jerk and may be equally acceptable.

Many other terms have appeared in individual cases for the third derivative, including pulse, impulse, bounce, surge, shock and super acceleration. These are generally less appropriate than jerk and jolt, either because they are used in engineering to mean other things or because the common English use of the word does not fit the meaning so well. For example impulse is more commonly used in physics to mean a change of momentum imparted by a force of limited duration [Belanger 1847] and surge is used by electricians to mean something like rate of change of current or voltage. The terms jerk and jolt are therefore preferred for rate of change of acceleration. Jerk appears to be the more common of the two. It is also recognised in international standards:

In ISO 2041 (1990), Vibration and shock - Vocabulary, page 2:"1.5 jerk: A vector that specifies the time-derivative of acceleration."Note that the symbol j for jerk is not in the standard and is probably only one of many symbols used.

As its name suggests, jerk is important when evaluating the destructive effect of motion on a mechanism or the discomfort caused to passengers in a vehicle. The movement of delicate instruments needs to be kept within specified limits of jerk as well as acceleration to avoid damage. When designing a train the engineers will typically be required to keep the jerk less than 2 metres per second cubed for passenger comfort. In the aerospace industry they even have such a thing as a jerkmeter; an instrument for measuring jerk.

In the case of the Hubble space telescope, the engineers are said to have even gone as far as specifying limits on the magnitude of the fourth derivative. There is no universally accepted name for the fourth derivative, i.e. the rate of change of jerk, The term jounce has been used but it has the drawback of using the same initial letter as jerk so it is not clear which symbol to use. Another less serious suggestion is snap (symbol s), crackle (symbol c) and pop (symbol p) for the 4th, 5th and 6th derivatives respectively. Higher derivatives do not yet have names because they do not come up very often.

Since force (F = ma) is rate of change of momentum (p, symbol clashes with pop) it seems necessary to find terms for higher derivatives of force too. So far yank (symbol Y) has been suggested for rate of change of force, tug (symbol T) for rate of change of yank, snatch (symbol S) for rate of change of tug and shake (symbol Sh) for rate of change of snatch. Needless to say, none of these are in any kind of standards, yet. We just made them up on usenet.

Now class, repeat after me. . .Momentum equals mass times velocity!Force equals mass times acceleration!Yank equals mass times jerk!Tug equals mass times snap!Snatch equals mass times crackle!Shake equals mass times pop!!

Z

[DAEDALUS]

I swear my high school physics instructor brought that in and read it to us...only problem is I left high school in 1990. Are you certain it was first published in 1996? I'm having a little problem with my own relativity.

[szh]

According to the site I found it at, yeah, 1996. But I do not know if it was circulating around earlier.

Z