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Category : Physics

Question : I am a seventh grade student and I would like to know why when air gets cold it contracts but when water gets cold it expands. Such as when a balloon is cold it shrinks but if you fill i water bootle up to the top and freeze it it will expand and maybe pop the bottle. Why is that?

Answer : A very astute observation. Most people don;t notice this strange inconsistent behavior of water. Considering that for almost all other materials the order of least to most dense is gas, liquid, soild, it stands to reason that water is odd for the fact that the solid form (ice) floats on top of the liquid form, and indeed forms on the top of the water first!

Water behaves in this strange way due a unique crystalline structure that water undergoes when freezing (becoming a solid). The open hexagonal structure actually takes up *more* space in this form than the same quantity of water in liquid stage. The end result is that the ice is of a lower density (less material per unit of volume) and thus is "lighter" than the same volume of water and floats. As to why it freezes on the top of the water as water is chilled from warmer temperatures it does indeed become less energetic and more dense. This continues down to about 4 degrees Celsius, just above freezing. At this point ice is at it's maximum density and this 4-degree water sinks to the bottom of whatever container is present (lake, sea, ice cube tray, etc) and warmer water moves in to take it's place. Cooler than 4 degrees C is where the crystalline structure begins to form which makes the water less dense as it moves towards freezing. Only after ALL the water in the container has been coooled to 4 degrees Celsius can further cooling take place. The most commong example of this is a lake whose top freezes over for ice skating in the winter. The whole body of water was at 4 degrees C before freezing from the top down (where the colder air cooled it). This also explains why the oceans don't usually freeze at all even during the coldest winters. They don't stay cold enough long enough for the entire depth to reach 4 degrees Celsius. And this answers the age-old question of:

What temperature was it at the bottom of the ocean on December 2nd, 1961 at 2:24 AM?

Answer - 4 degrees Celsius... because it always is.

Paul Doherty
Rating :

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FAQId : 1754356
Subject : How do sound (and radio) waves travel?

Question : I understand that a wave must have a medium to travel through (it can't travel through a vacumm)as it's the vibration of molecule that carry the wave. I assume that each molecule knocks in to the next one, passing on energy, which causes that to vibrate and so on. I also assume that on each 'knock' energy is lost, until the energy is so small that the wave can not be detected.
Sound waves travel in the audiable spectrum, radio is a sound wave that is added to a carrier wave which is outside of the audibility and then the radio receiver converts this back to audible sounds when it receives it. Each radio station uses a different frequency carrier wave.
(1)How do all these different frequencies (sound, radio, TV, mobile phone) travel? (2)How do molecules vibrate at all of these frequecies at the same time? (3)Are we constantly surrounded by molecules vibrating as a result of radio / TV / Mobile phone? (4)Do any of the molecules in our bodies vibrate due to these waves?
Hope there aren't too many question there for you.

Answer : Yes, radio waves are the same phenomenon as visible light - just of a longer wavelength. It is pure energy (as opposed to a mechanical vibration such as sound waves, which are truly defined by their medium) which is why is needs no transmission medium. Sunlight is a perfect example - it is a mishmash of ER frequencies and travels a vast distance to arrive at Earth in the same form it was when is was emitted.

Paul Doherty, CNA, CNE, MCP+I, MCSE, B.A.
http://members.home.net/iqueue

Answer : The main thing you are missing here is that of the phenomena you are discussing only one is a physical wave - sound. Radio waves, microwaves (mobile phones), and television are all signals carried on *electromagnetic waves*. Electromagnetic radiation is a form of pure energy and requires no medium for transmission (infact mediums just get in the way - that's why light from the sun is slowed slightly and bent by the air in our atmosphere or by water when looking into a pool or bathtub).

As far as the molecules of your body oscillating in rhythm to some of these frequencies of radiation I'd have to say that yes some do. And some frequencies are more powerful than others - some of which can cause cell damage and our not so nice friend, cancer.

I hope that answered your question(s)...

Paul Doherty, CNA, CNE, MCP+I, MCSE, B.A.
http://members.home.net/iqueue

Answer : 1. In the sun light is generated as mass is *directly* converted to energy from mass. The sun is a huge nuclear fusion reactor, turning hydrogen atoms into helium and other light elements. The disparity between the mass-per-nucleon (namely the huge reduction in MPN going from hydrogen to helium) is where this ER and heat come from.

2. Photons are "re-emitted" - the mass that makes up any object can be thought of as being "in tune with" certain frequencies of light, much like a tuning fork. If you shine white light on the object all frequencies are absorbed as heat except the ones to which the material is "resonant". The resonant ones energy goes into the elevating into higher orbits and re-emission of another photon.

3. Yes... Answered in #2 above.

4. The object re-emits those frequencies to which it is attuned.

5. Light travels and interacts both as a wave (like gravity or magnetism) *and* as a particle. This is one of the great apparent paradoxes of light. So I would say that interference patterns would be the result, with constructive and destructive interference the result. But I can not definitively state this without research and I haven't the time to do so tonight.

6. As for how a radio transmitter works here is a good description of the rapid oscillating electric charges that run up and down the antenna:

"Electromagnetic waves are created whenever electrically charged particles change speed or direction; whenever they accelerate. Since there are accelerating electric charges everywhere--thermal energy keeps them moving about--there are also electromagnetic waves everywhere. But the radio waves used in communications systems are generated deliberately by moving electric charges back and forth. When charges are sent up and down a radio antenna, these charges are accelerating and they form complicated electric and magnetic fields that include electromagnetic waves. Once launched, those electromagnetic waves propagate through space at approximately the speed of light."

A radio station launches a radio wave by moving electric charges rhythmically up and down their antenna. As this electric charge accelerates back and forth, it produces a changing electric field--a structure in space that pushes on electric charges--and a changing magnetic field--a structure in space that pushes on magnetic poles. Because the electric field changes with time, it creates the magnetic field and because the magnetic field changes with time, it creates the electric field. The two travel off across space as a pair, endlessly recreating one another in an electromagnetic wave that will continue to the ends of the universe. However, when this wave encounters the antenna of your radio, its electric field begins to push electric charges up and down on that antenna. Your radio senses this motion of electric charges and thus detects the passing radio wave.

And continuing...

"To convey audio information (sound) to you radio, the radio station makes one of several changes to the radio wave it transmits. In the AM or Amplitude Modulation technique, it adjusts the amount of charge it moves up and down its antenna, and hence the strength of its radio wave, in order to signal which way to move the speaker of your radio. These movements of the speaker are what cause your radio to emit sound. In the FM or Frequency Modulation technique, the radio station adjusts the precise frequency at which it moves charge up and down its antenna. Your radio senses these slight changes in frequency and moves its speaker accordingly."

The last gleaned from the website:

http://rabi.phys.virginia.edu/HTW//

--
Paul Doherty, CNA, CNE, MCP+I, MCSE, A.A., B.A.
http://members.home.net/iqueue
Home of PC DiskMaster and other Windows utilities

Answer : The energy can come from heat, motion, electrical or magnetic forces, or from other sources of ER.

When an atom becomes excited, by physical or electrical means, it's electrons become elevated to levels above their normal orbits. These electrons then drop back to their normal unexcited state and in the process give off the energy they gained. Since the orbits are at definite levels apart from each other, and since the electrons cannot reside between these levels, the energy given off by an electron going through this de-excitation process is said to be quantized. Quantization in this usage means that the energy is given off in discrete steps of energy. This excitation and atomic quantization is where we get some of the things familiar to us. As you probably already know electromagnetic radiation (I'll call it ER from here on out) in the ranges that our eyes use is generally called "light". So light is produced by this same mechanism - electrons get excited up to a higher-than-normal orbit, and then de-excite, giving off the energy they had gained in the form of a photon (quantized "piece" of ER).

Here's a good example of the quantization of light. I'm sure you've seen the so-called neon signs in convenience stores and such? Those signs are an excellent example of the quantized nature of electron orbits. Those lamps contain a pure gas - in the case of the bright red ones it's neon. The particular combination of electron excitation/de-excitation steps available to the neon atoms is what gives neon it's characteristic red color. Argon is another gas used in these lights and has a blue color for the same reason. Each type of gas has it's own characteristic pattern of available electron orbit hops that give it unique color. Contrast these types of lights with an incandescent light like in your house or on your car. These use a metal filament which when heated glows and gives off light. the same process if happening as in the gas but we get (closer to) pure white light from this type of bulb. Why? It's because now, instead of the limited nmber of combinations of electron orbit hops we had with a gas (where atoms are relatively far apart), we have a solid material with atoms shoved close together. The result being that electrons who make a hop to higher energy orbit in one atom may very well de-excite into a nearby atom making the energy patterns closer to infinite which also makes the frequencies of emitted ER nearly infinite - white light. A flourescent bulb works like a neon light but produces white light. How is that? It uses mercury vapor inside the tube, which when a current is passed through excites and gives off the standard limited number of patterns a gas can produce. But this light isn't even visible - it's ultraviolet in frequency. the white light actually comes from the spray coating on the inside of the tube - this solid material absorbs, and becomes excited by, the UV light and in turn gives off it's own less-limited pattern of white-ish light.

Paul Doherty, CNA, CNE, MCP+I, MCSE, B.A.Sc.
http://members.home.net/iqueue
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FUQuestion : So are radio waves etc classed as 'light' waves?
How does this energy travel from one place to another?

FUQuestion : Paul,

You refer to Radio (and light) waves as pure energy, but what is pure energy? and where does this energy come from?

Regards,

Richard.

FUQuestion : Paul,

Thanks for all your answers. They are very interesting. Hope you don't mind me answering so many follow up questions. Please let me know if you do.

I think that I understand how light works now, however could you tell me if I'm on the right track.
I have number my questions and assumptions so that it is easier for you to reply.

Atoms in a light bulb are excited by electricity which causes their electrons to move into a higher orbit. When they fall back to their original orbit they give out energy [photon]. (1)I assume that in the sun this is caused by a chemical reaction(?). We see objects because light [photons] bounces off them and are then enter our eye which the brain interpretates.(2) Do the photons actually 'bounce' or does the photon that hits the object cause a new photon to be omitted? (3) I assume that we see colour because a red object only reflects red light, a yellow object only yellow light etc.
(4) So if I have the above right, then an objects colour depends on the different atoms within an object. Each different atom emits a different amount of red or blue or green which 'combine' to produce the final colour.
(5) If a near infinite number of photons are travelling in all direction all of the time, then do these photon colide and if so what happens?

The different colours (different frequencies of photons) that we see are due to different atoms having different distances that their electrons travel between the normal and excited state. Going back to one of my first topics, (6) how are radio waves created? I appreciate that these 'waves' are just photons with a different frequency (energy level) but how does a transmitter create them?

Thanks again for your answers.
Regards,
Richard.


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FAQId : 2669188
Subject : physics,motion

Question : dear respected sir ,

I AM A BIT WEAK IN PHYSICS SO I NEED YOUR HELP. WHAT IS MOTION ,POTENTIOLENERGY ,KINETICENERGY SAY WITH SIMPLE EXAMPLES .KINETICENERGYS FORMULA IS MVSQUAR.WHAT IS COLLUSION AND WHO THE MOMENTUM
BEFORE IMPACT =AFTER IMPACT

Answer : Motion is simply matter that is not at rest with regard to another object. Like a baseball thrown through the air.

Kinetic energy is energy of motion. The baseball has kinetic energy in it's motion as it moves across the sky. Kinetic energy becomes other forms of energy when the previously moving object stops. For example when the baseball strikes the ground part of it's kinetic energy becomes heat. A hammer striking a nail also makes the nail hot, as the hammer's kinetic energy is transferred as heat into the nail (and hammer).

Potential energy in this example would be exemplified by holding a baseball motionless above the ground. The baseball has potential energy due to it's elevation. If the baseball were to be released it would fall, and it's potential energy would be converted to kinetic energy as it falls until, by the time it reaches the ground, all the potential has been converted to kinetic (it's reached it's maximum speed just as it impacts the ground). A good way to think of potential energy is that it exists *because work was required to get the baseball to the height iwas at to begin with* and the energy used for that purpose is what we mean by potential energy.

Momentum is the product of mass and velocity. The more massive an object is, or the faster it travels, the more momentum it will have. Momentum is what makes things hard to stop. A slow baseball is easy to catch and doesn't hurt much. A fast baseball (same mass of course) hurts a lot. This is why a bullet is so dangerous - it has a lot smaller mass than a baseball but it's travelling much faster so it's momentum is great.

To determine final motion in an inelastic collision (where the objects don't deform on impact) you compare relative velocities (speed *and* direction of travel) and masses and you can then easily see the result. For example with two identical-shaped spheres - one of lead and another of aluminum (say the lead has a mass of 10 and the other a mass of 5). If we assume the objects are travelling the same speed and hit directly head-on into each other the result will be (minus a little lost momentum as heat from the collision) that the aluminum sphere will now have a negative direction of motion (backwards from where it came) at half the speed it held when it approached. The same result would happen if the spheres were the same mass (made of the material) and one was travelling twice as fast as the other.

--
Paul Doherty, CNA, CNE, MCP+I, MCSE, A.A.Sc., B.A.
http://members.home.net/iqueue
Home of PC DiskMaster and other Windows utilities

Rating :
Rating :

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FAQId : 2677367
Subject : specific heat capacity

Question : supose that we are sitting in jamaica. there is a jaccuzi on our terrace and a few rocks beside it . both of them recieve the same amount of sunlight. when night falls which is a better way to keep the water in the jaccuzi warmer
a)leaving the water as it is in the jaccuzi
or
b)putting the sun-baked rocks inside the jaccuzi
explain

Answer : The answer depends on two things:

1) Which (the rock or the water) has a higher temperature upon the initial introduction of the rock to the water

2) Which has a higher specific heat - the water or the rocks?

I would suggest that water is one of the higher of known materials with regard to specific heat (that's why it's used in radiators in cars and hot water bottles).

For the unintitiated to the concept of specific heat it really comes down to a measurement of a material's resistance to a change in temperature. Water resists change highly thus it's specific heat is high. A great example of this is the beach where water and sand meet. During the day when the sun is out, barring any major weather patterns, the wind will blow in from the sea towards the beach. This is due to the sand heating quickly (low specific heat) in the sun, surpassing the temperature of the water (high specific heat) which is slower to warm. This produces convection currents in the air as the warmer air over the sand and land rises to be replaced by cooler air moving in from over the water in a circular fashion. But at night, once the sun goes down, specific heat again is shown as the rocks cool more quickly (remember specific heat is a resistance to *change* in temperature - this includes cooling as well as heating) than the water. The result is that the convection currents are reversed with the water retaining it's heat longer and creating convection currents that now move in the opposite direction (i.e. the wind now blows out towards the sea).

Now back to the rock/water question. I would suggest that *if* the rocks are hotter than the water I'd put them in, until their temperature was in equilibrium with the water (thus they gave up their additional heat to the water). Then I'd pull the buggers out of there. Not because of any further impact on temperature, but simply because who wants friggin rocks in their jacuzzi? :-)

--
Paul Doherty, CNA, CNE, MCP+I, MCSE, A.A.Sc., B.A.
http://members.home.net/iqueue
Home of PC DiskMaster and other Windows utilities

Answer : The answer depends on two things:

1) Which (the rock or the water) has a higher temperature upon the initial introduction of the rock to the water

2) Which has a higher specific heat - the water or the rocks?

I would suggest that water is one of the higher of known materials with regard to specific heat (that's why it's used in radiators in cars and hot water bottles).

For the unintitiated to the concept of specific heat it really comes down to a measurement of a material's resistance to a change in temperature. Water resists change highly thus it's specific heat is high. A great example of this is the beach where water and sand meet. During the day when the sun is out, barring any major weather patterns, the wind will blow in from the sea towards the beach. This is due to the sand heating quickly (low specific heat) in the sun, surpassing the temperature of the water (high specific heat) which is slower to warm. This produces convection currents in the air as the warmer air over the sand and land rises to be replaced by cooler air moving in from over the water in a circular fashion. But at night, once the sun goes down, specific heat again is shown as the rocks cool more quickly (remember specific heat is a resistance to *change* in temperature - this includes cooling as well as heating) than the water. The result is that the convection currents are reversed with the water retaining it's heat longer and creating convection currents that now move in the opposite direction (i.e. the wind now blows out towards the sea).

Now back to the rock/water question. I would suggest that *if* the rocks are hotter than the water I'd put them in, until their temperature was in equilibrium with the water (thus they gave up their additional heat to the water). Then I'd pull the buggers out of there. Not because of any further impact on temperature, but simply because who wants friggin rocks in their jacuzzi? :-)

--
Paul Doherty, CNA, CNE, MCP+I, MCSE, A.A.Sc., B.A.
http://members.home.net/iqueue
Home of PC DiskMaster and other Windows utilities

Answer : Don't forget to rate the answers you receive on AskMe.com...

Answer : Whoops - hit the submit button twice.

Also in my sentence above:

But at night, once the sun goes down, specific heat again is shown as the rocks cool more quickly (remember specific heat is a resistance to *change* in temperature - this includes cooling as well as heating) than the water.

That reference to "rocks" should be "sand". Was thinking ahead to the rock question I guess... :-)


End : This conversation is closed because the Expert has used it in a FAQ.

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FAQId : 2692874
Subject : quantum physics

Question : Is it possible to synthesize excited bromide in an argon matrix? if so, how?

Thank you
Brian

Answer : Yes - but only if you use dry-ice slugs to obtain free coffee, and if you're prepared if gravity suddenly reversed itself! ;-)


--
Paul Doherty, CNA, CNE, MCP+I, MCSE, A.A.Sc., B.A.
http://members.home.net/iqueue
Home of PC DiskMaster and other Windows utilities

Answer : And of course you know that, if successful, that this procedure is like lazing a stick of dynamite and can be quite hazordous?

Be careful out there people!

--
Paul Doherty, CNA, CNE, MCP+I, MCSE, A.A.Sc., B.A.
http://members.home.net/iqueue
Home of PC DiskMaster and other Windows utilities

Answer : Where is my spelling this morning? Hazardous...
Rating : I didnt think youd get it. Good job!!

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FAQId : 3086744
Subject : vision

Question : If in subtractive colour (i.e. mixing of paints) the resulting colour is determined by the overall reflective properties of the paints involved, then how come black isn't the result of a mixture of two or more different colours?

For example if red paint reflects red light and absorbs the other frequencies of light and yellow reflects only yellow and absorbs the others, then surely when the two are mixed the red pigment will absorb yellow light and the yellow will absorb red resulting in no light being reflected. Can you explain why this is not so?

Answer : It is not so because you have mistakenly identified red as a primary subtractive color when it is not. Red is a primary *additive* color. The three primaries for subtractive coloring (as in a printing press) are:

yellow
cyan
magenta

Where each overlaps another a color is produced by the mechanism you described. For example:

When yellow and cyan overlap the resultant (left over) color is green. When magenta and yellow are used the result is red. Only when white light passes through all three of these subtractives are all frequencies removed for a result of black.

--
Paul Doherty, CNA, CNE, MCP+I, MCSE, A.A.Sc., B.A.
http://members.home.net/iqueue
Home of PC DiskMaster and other Windows utilities




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FAQId : 3239956
Subject : Physics Question

Question : I am a student at BU in an Elementary physics class. I have one problem that I can't seem to get an answer to. The problems reads as follows:

At serve, a tennis player aims to hit the ball horizontally. What minimum speed is required for the ball to clear the .90m high net about 15.0m from the server if the ball is "launched" from a height of 2.50m? Where will the ball land if it just clears the net (and will it be "good" in the sense that it lands within 7.0m of the net)? How long will it be in the air?

I would greatly appreciate your help on this problem

Thanks,
emarlo

Answer : OK, here we go.

distance from server to net - 15m
height of net - .9m
height of ball at horizontal launch - 2.5m
maximum distance travelled for "good" shot - 22m (15m + 7m on other side of net)

The first thing we need to find is how far the ball can fall before it will not clear the net. It's starting at 2.5m and will not clear after the level of the net, .9m, so we simply subtract .9 from 2.5m and get 1.6 meters. This is the maximum distance we can fall before crossing the net.

So now we need to know how long that fall (1.6m) takes. Since the gravitational acceleration is unaffected by our shot speed we can safely calculate this time by this:

1/2gt^2 = 1.6

(1/2 * g (9.8m/sec))

4.9*t^2 = 1.6

(divide both sides by 4.9)

t^2 = .33

(take the square root of each side)

t = 0.57 seconds to fall 1.6m

Now that we know the time to fall 1.6m we can calculate how fast our ball must travel to cover the 15m from server to net so the ball will cross the net.

0.57 * x = 15m

(divide both sides by .57)

x = 26.32 m/sec

So we must strike the ball at 26.32m/sec speed in order to arrive at the net height in our required time interval of .57 seconds.

Now that we know part of the answer (our minimum shot speed) we can calculate how far the shot will travel at that speed before it hits the ground, and where it will be when it hits. We do this by measuring the time it takes for the full initial ball height (2.5m) to be lost:

1/2gt^2 = 2.5m

(1/2 * g (9.8))

4.9 * t^2 = 2.5m

(divide both sides by 4.9)

t^2 = .51

(take the square root of both sides)

t = .71 seconds

This is the time it will take from launch until the ball hits the ground. Now all we need to do to find the distance travelled is multiply this time by our shot velocity:

.71 * 26.32 = 18.69m

So our ball will travel 18.69m before hitting the ground. The full distance the ball can travel and still be inside the "good" range for a serve is 22m so our shot will be good, and will strike 3.9m away from the net on the other side of the net (18.69m - 15m to net = 3.9 more to travel).

--
Paul Doherty, CNA, CNE, MCP+I, MCSE, A.A., B.A.
http://members.home.net/iqueue
Home of PC DiskMaster and other Windows utilities

Rating : Very thorough. I appreciate your help. Thanks again.
Rating :

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FAQId : 4747923
Subject : acceleration due to gravity.

Question : How far will a 20 kg rock in 5 seconds? We are
in disagreement about the answer.

Solution 1: Using 9.8 m/sec/sec= (V final- O m/sec) / 5

We came up with 49 m/sec.

Using the formula for speed we went 49 m/sec times 5 sec
and came up with a distance of 245 meters.

Solution 2: If you manually add the acceleration of gravity
You come up with 156.8 meters.

Which is correct and why?

Answer : I get 122.5 meters of fall after 5 seconds. I think you made a slight mistake when you got 49m/sec and then multiplied *it* by 5 seconds. The thing to remember that 9.8m/sec is the amount of speed *added* over each second of fall. For example if you drop a rock and let it fall one second *at the end of that second* it will be travelling at a rate of 9.8m/sec, but it won't have travelled that far. Why is that? Because at the beginning of the second it was holding perfectly still, and at the end it was travelling at 9.8m/sec with smooth acceleration all in between. So you must find it's *average* speed over that second by dividing the time in half (we're multiplying by 1/2 (.5) but it's the same thing). The formula for the distance fallen when you know the time the object has fallen is:

1/2gt^2

where g is 9.8m/sec for gravity
t is time in seconds for the fall

So when we plug in your numbers:

1/2 * (9.8 * 5^2)

1/2 * (9.8 * 25)
1/2 * (245)

= 122.5m of fall after 5 seconds.

If you want to know how fast the object is falling at the end of any particular second just multiply the gravitational acceleration by the number of seconds of fall:

5 seconds of fall:

gt

9.8 * 5 = 47.5m/sec at the end of 5 seconds


For more info see one of my questions I previously answered on a tennis shot that deals with gravitational fall:

http://www1.askme.com/MyXpertise.asp?pm=va&method=faq&cid=852&viewfaq=1&page=1&vid=3239956


--
Paul Doherty
http://members.home.net/iqueue
DOS/Windows Utilities


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FAQId : 5002282
Subject : rain

Question : does one get wetter running or walking in the rain? This is assuming that one has no umbrella.

Answer : Well let's compare two situations:

1) Standing perfectly still in the rain

2) Running at full sprint in the rain

In situation #1 (we're assuming that the rain is falling perfectly vertical for this discussion) you'll note that there isn't much surface area you're exposing to the rain - mostly just your head and shoulders (unless you've been partaking of the pasta a bit too much! ;-)

In situation #2 you are now exposing your head and shoulds *AND* almost your entire frontal area to raindrops, which would result in you getting at least as wet if not more wet than in situation #1 (perhaps only equal due to the lesser time during which you are exposed to the rain since you're running).

So I would still call it a draw. You guys keep your money and shake hands. :-)


--
Paul Doherty
http://members.home.net/iqueue
DOS/Windows Utilities

Answer : There is no difference (amazingly I too have pondered the question! hehe). If you think about it this way running only changes *where* you get wet. By running you are catching up to raindrops in front of you (that subsequently hit your front and legs) that would normally have fallen in front of you. So by running you may find yourself soaked in front but relatively dry in the back. You can't win for losing huh?? :-)



--
Paul Doherty
http://members.home.net/iqueue
DOS/Windows Utilities

Rating :

FUQuestion : Thanks...it would make sense then that if you run, you're spending less time so you get less wet. (I ask b/c this is a bet)

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FAQId : 5002300
Subject : measuring volume

Question : what are the different methods of measuring volume?

Answer : I don't know about multiple ways. The best way I know of to get the volume of an irregular-shaped object:

1) Fill a container larger than the object completely full of water.

2) Place a larger container below that one to catch the water.

3) Attach the object to be measure to a string (or if it's a bouyant object to a stick) and submerge the object completely in the top tub. This will displace water into the tub below. Submerge it slowly so no spills or extra "waves" are produced.

4) Now measure the volume of water captured in the tub below. That volume is the same as the object you submerged.


--
Paul Doherty
http://members.home.net/iqueue
DOS/Windows Utilities


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FAQId : 5002365
Subject : Terminal Velocity

Question : A free falling body may experience terminal velocity. Please explain terminal velocity in terms of a free falling body. Thank You!

Answer : Terminal velocity is simply the maximum unassisted speed that an object can fall in air. Two aspects of an object contribute to what this speed will be - it's mass (weight) and it's surface area (amount of the object exposed to air). What happens is as the speed of the fall increases so does the effect of the air your strike as you fly downwards. If you continue to accelerate long enough (like in a sky dive from altitude) evetually you will stop accelerating when the force of the air resistance you enounter equals your weight.

Human beings are large and thus tend to have a large volume relative to our surface area. So our terminal velocity is quite high - around 125 MPH. An ant or a feather have very little volume and tons of surface area (think of the tiny wisps that make up a feather, or the skinny legs of an ant) so their weight will be equalled at a far lower speed. The terminal velocity of an ant is likely around 3 feet per second. That's why you can drop an ant from the ceiling and he'll walk away. So that to a human and they'll be lucky to not be heading to the hospital with an injury!


--
Paul Doherty
http://members.home.net/iqueue
DOS/Windows Utilities

Rating :

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FAQId : 5002411
Subject : Satellite Orbit

Question : Please explane how satellites orbit the earth. Why do they continue to orbit and not fall to earth? Why do they stay in orbit and no "run off" into space? Thank You!

Answer : A satellite *does* fall towards Earth. The gravitational force at that distance is greatly diminished but it's still quite present. The Earth curves in a fairly uniform fashion - every X distance travelled horizontally equates to Y drop in altitude. At ground-level it's about 4.9 meters of drop for every 8 kilometers of lateral distance. In space the distances are greater but the concept is the same. For the satellite to experience the same rate of fall (and maintain its distance from the Earth) it needs to travel a horizontal distance during each second of fall that will bring it to the same height above the ground as it was at the beginning of the second. So in essense the satellite "falls around the Earth" rather than into it. If the satellite's speed begins to slow it will be what is called a "decaying orbit" where it is no longer travelling the lateral distance required each second, so therefore it is now is a "spiral" of sorts, losing altitude with each second. If it goes faster than is needed to maintain the orbit it will gradually gain altitude and eventually launch out into space.


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Paul Doherty
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DOS/Windows Utilities

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FAQId : 5002476
Subject : why sky is blue

Question : How come sky is blue ?
Thanks for your time !!!

Answer : The sun produces light of almost all frequencies (white light). When that light attempts to penetrate our atmosphere some of the frequencies interact more than others. Particularly the higher frequencies of blue and ultraviolet (just above our range of perception). They set off sympathetic virations in the atomic structures of the various molecules that make up our air and these atoms in turn release photons of light in the same frequency range. Much like a bunch of tuning forks setting each other off. This scattering effect is what colors the sky blue, as those atoms respond to the frequencies closest to their own. Interstingly, if you could see ultraviolet light with your eyes you would find that the sky is actually ultraviolet in color, not blue since ultraviolet has the highest resonance with the air molecules.


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Paul Doherty
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DOS/Windows Utilities

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FAQId : 5480380
Subject : Light

Question : Can you explain refraction of light?

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Answer : Refraction occurs when light waves do not travel in a perfectly-perpendicular path through a transparent medium like glass or water. The effect is that of "bending" of the light such that the arrival point the light eventually strikes is not in a direct line from where it entered. The classic example is that of the fish floating in a bathtub of still water. When you stand outside the tub and look at the fish he appears to be floating several inches below the surface when in actuality he is much deeper in the tub than it initially appears. Why this happens is due to the speed of light through each medium. In air light travels nearly as fast as in a vacuum - around 99%. In water it travels much slower - around 75%. What happens in refraction is that light takes the *shortest time path*, no the *shortest distance path*. Since it travels slower in the water the light travels from the fish in a more directly-upwards manner whereupon it exits the water and then curves back into the direction of travel. Since your eye sees light as a line-of-sight phenomenon you see the fish as being where the light rays strike your from, rather than where he is. It's a bit hard to describe without pictures but here's a good analogy that helps a lot. Think of the front of the light wave as a wave-front that has width like one of those old push lawnmowers with the blades. It took a lot of effort to move the mower when it was pushing through grass you'd neglected to mow for the last 4 weeks. :-) But when it was on the sidewalk it moved much easier. Now imagine you were pushing it along the sidewalk and then angled it a bit to the right so the mower entered the grassy area - what happens as the right edge "bites" into the grass? What happens is that the mower is pulled even further to the right that you had it but once the whole mower is on the grassy area you plow straight ahead without change. Now imagine you reach the far side of the rectangular grassy are you were traversing. The right edge will still be leading as you exit onto the pavement and what happens then? The right edge speeds up slightly and by the time the mower exits fully onto the pavement the right side will have advanced a bit further changing your angle back to the *original angle you had upon first entering the grassy area on the other side*. So what happened is you had one angle on entering and your right side slowed down, which pulled you closer to the perpendicular by a few degrees (the taller the grass ("the denser the medium") the more your course was altered). Then you traversed the grassy area at this angle and with a slower speed. Once you reached the far side and began to exit the grassy area onto the pavement your right side sped up and by the time the whole mower was off the grass you were back at your original angle of travel. This is what light does when it travels between two different mediums. When it strikes a slower moving medium it bends towards the perpendicular, travels more slowly through the medium, and then exits at it's original incident angle.

So since we know that light bends in towards the perpendicular on *entering* a denser medium it stands to reason that upon *exiting* a denser medium it will bend *away* from the perpendicular. It does and this is why our fish appears to be higher than he is. The light travels more vertically as it traverses the water, and upon striking the surface (think mower exiting the water) it bends away from the vertical and to your waiting eye. Since your eye sees light as a "straight-line-only" affair you see the fish as being directly where the light appeared to come from.

Drawing this out on a piece of paper will help you understand it even better. Just draw a line for the water, then a fish somewhere below, an eye to observe it, and then draw the light path imagining the light working hard to get through the water (grassy area) and speeding up as it exits into the air and you will find that to get the beam to the observer's position will create a false image of the fish higher than his true position.


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Paul Doherty
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FAQId : 6645905
Subject : physics

Question : If plane A flying at an altitude of a 1000ft drops a 100# bag and plane B flying at an altitude of 2000ft also drops a 100# bag, will the speed of the bag from plane B on arrival on the ground be twice as fast as the one from plane A?

Answer : Both bags are identical in weight (and presumably shape) - they will be travelling the same speed when they strike the ground.

Why? Because of a thing called terminal velocity. Terminal velocity is the fastest unaided speed an object can fall in air, and is determined by the object's shape (surface area) and weight. Once an object has accelerated to a speed where the air resistance it encounters is equal to it's weight at that altitude it will no longer go any faster.

Both bags will accelerate from gravity at the same rate. While the second bag falls longer than the first, both will have reached terminal velocity long before hitting the ground, thus they will be travelling at the same speed.

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Paul Doherty
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DOS/Windows Utilities

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