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Parte da "Série de Ciências da Bell System", composta por nove especiais educativos produzidos para a AT&T Corporation e originalmente transmitidos pela TV entre 1956 e 1964. Este episódio, apresentado pelo Dr. Frank Baxter, aborda as propriedades do tempo e como o monitoramos.
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00:27A CIDADE NO BRASIL
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01:00We will explore.
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03:19Mas onde vou colocar as mãos?
03:22Bem...
03:26O tempo é?
03:35Se você não conhece, descobre.
03:37Sim, senhor.
03:47Before we go on with the story,
03:49there's one more thing we've imagined here on Planet Q.
03:52An observatory.
03:54And inside of it, this.
03:58We'll call it an Earthscope.
04:00We'll use it to examine some of the things
04:03that people on Earth have found out about time.
04:07Come in.
04:10Hello.
04:12Say, we've run into a little problem.
04:15I wonder if you could answer a question.
04:18The king wants to know, what time is it?
04:21Oh, yes.
04:22What time would he like it to be?
04:24Oh, the correct time.
04:25You see, we're setting our clock
04:26so that we can do everything on time.
04:28Well, tell him to set it any place he likes.
04:31Thank you.
04:38Any place?
04:39That's right.
04:40Well, let's see.
04:42Suppose we use the Earthscope screen.
04:45Bring the Earth into focus.
04:48See what time it is down there.
04:57Is that the correct time?
04:59It is for London, England.
05:02But what time is it?
05:04They call it noon.
05:06That also happens at what they call midnight.
05:10Well, is midnight before or afternoon?
05:12Twelve hours after or twelve hours before.
05:17It all depends.
05:18On what?
05:19Whether you're talking about yesterday or tomorrow.
05:24But they had to start somewhere.
05:27How did they go about it?
05:30The rhythms of nature probably gave man his first awareness of time.
05:34Man must have observed the recurrence of natural phenomena.
05:38The movements of the sun.
05:44The moon.
05:46The stars.
05:48He noticed that these events in the heavens
05:51seemed to coincide with events on Earth.
05:54The spring and the rains.
05:59The summer growth of leaves.
06:03The autumn ripening of fruit.
06:07He thought the moon, sun, and stars controlled his crops.
06:12This was understandable because to him,
06:14the sun, the moon, and the stars were gods.
06:20People began studying the heavenly bodies.
06:22As they made notes of their changing positions,
06:26the science of calendar making began.
06:31Almost every civilization labored to devise a workable calendar.
06:36Some of them were based on the cycles of the moon.
06:41Others, on the movements of the sun.
06:46But none of them came out just right.
06:53Even the Gregorian calendar,
06:55the one used today,
06:57is not perfect.
07:02Wouldn't you think by now they'd have a perfect calendar?
07:05No.
07:06It's not so easy.
07:09You see,
07:10the time it takes the Earth to rotate on its axis
07:13is a day.
07:15But the time it takes the Earth to revolve around the sun
07:20is a year.
07:22But a year comes out to 365 days,
07:26five hours,
07:2848 minutes,
07:29and 46 seconds.
07:30Oh.
07:32And the problem is what to do
07:33with that leftover fraction of a day.
07:36That's why they add an extra day
07:38every four years.
07:40Except, of course,
07:42when that year falls at the beginning of a century.
07:45Of course.
07:46But they add the extra day
07:48every fourth century.
07:50Of course.
07:52But it's still off 26 seconds a year.
07:55So they call it a calendar.
07:58But it's still off 26 seconds a year.
08:02It's very interesting.
08:04I thought so.
08:05And after we get the clock set,
08:07we'll get a calendar.
08:08But one thing at a time.
08:10Yes, sir.
08:11Just explain to him
08:13that we need to know the time
08:15to eat,
08:16to sleep,
08:17and so forth.
08:18Just any time won't do.
08:20Well,
08:21early man didn't regulate
08:23his habits to a clock.
08:25All animals,
08:26including man,
08:27and plants, too,
08:29have a built-in time sense.
08:31I didn't know that.
08:37It's long been considered
08:39a wonderful phenomenon of nature
08:40that plants seem to know
08:42when to flower
08:42and set their seeds
08:44at just the right time.
08:46That furry animals
08:48have a way of knowing
08:49when to change
08:49to their heavy coats
08:52before the first
08:53cold winds of winter.
08:56That birds,
08:58by some instinct,
09:00know just the right time
09:01to set out
09:01on their long migrations
09:03and always bear their young
09:05in a season favorable
09:07for survival.
09:09It was once commonly supposed
09:11that these seasonal occurrences
09:12are triggered
09:13by changes in temperature.
09:16But investigations have shown
09:18that plants
09:18and animals
09:19depend mostly
09:20on timing mechanisms
09:21within themselves,
09:23internal clocks.
09:25Internal clocks?
09:27That's right.
09:27Interested?
09:30Yes.
09:32This clock,
09:33or biological timer,
09:35determines the seasons
09:36by the changing lengths
09:38of day and night,
09:39particularly the periods
09:41of darkness.
09:42Darkness?
09:43Yes.
09:46Here is Dr. Anton Long,
09:49plant physiologist
09:51and director
09:51of Earhart Laboratory,
09:53who has been experimenting
09:55with the timing mechanism
09:56of the cocklebur plant.
09:58The autumn flowering cocklebur
10:00needs about eight and one-half hours
10:03of continuous darkness
10:04to flower.
10:05As autumn comes,
10:07the nights get longer.
10:08when they get long enough
10:09for the plant's timer
10:11to tick off
10:11eight and one-half hours
10:13of darkness,
10:14the flowering begins.
10:19If the nights get longer,
10:21that means the days
10:22get shorter.
10:23How did they know
10:24it wasn't the short days
10:25that did it?
10:26Well, they didn't.
10:29So they conducted
10:31a series of experiments
10:32under artificial light.
10:33They simulated
10:34various proportions
10:36of night and day.
10:38From these experiments,
10:39scientists proved
10:41that it is the darkness
10:42that the cocklebur plants measure.
10:44And all plants and animals
10:46have one of these
10:47internal clocks?
10:49Well, some plants and animals
10:51have another kind
10:52of timing mechanism.
10:53This one doesn't measure
10:55darkness or any apparent
10:57outside influence.
10:58It regulates the activities
11:00of the plants and animals
11:01by time periods alone.
11:04Bean plants, for example,
11:07have this kind
11:07of continuous clock.
11:09They raise or lower
11:10their leaves
11:11without much regard
11:12to temperature,
11:13light, or darkness.
11:14Some animals,
11:15like the hamster,
11:17also have a continuous clock.
11:19The hamster's daily cycle
11:21is broken into definite periods.
11:24A period for eating,
11:29a period for sleeping,
11:36a period for exercising.
11:40His clock continues to run,
11:43to regulate his cycles,
11:45even though he lives
11:46in continuous darkness
11:47or continuous light.
11:49Practically every kind
11:50of living organism
11:51seems to have some sort
11:53of built-in time sense.
11:56Scientists all over the world
11:58are trying to find out
11:59how internal clocks work.
12:02When they do find out,
12:03it may mean that the cycles
12:05of plants and animals
12:06can be controlled,
12:07directing their energies
12:09into producing more food,
12:11more clothing,
12:13more shelter.
12:17That's quite incredible.
12:19But one thing puzzles me.
12:21If man has a built-in clock
12:23like those plants and animals,
12:25why did he need other clocks?
12:27He found that his internal time sense
12:30was not adequate for his needs,
12:32which are far more complicated
12:34than those of plants and animals.
12:36Man had to find other means
12:38of measuring intervals of time.
12:40So he invented a clock.
12:42A type of clock.
12:45Yes.
12:47Actually, he stuck a stick
12:49in the ground
12:49and told time
12:50by the moving shadow.
12:54This became the basis
12:55of the sundial.
13:02The Egyptians developed a clock
13:05that measured time
13:06with dripping water.
13:07And there were other clocks
13:09that measured time
13:10with flowing sand.
13:12None of these early timekeepers
13:15could measure small intervals
13:16of time with any accuracy.
13:19In 1583,
13:21Galileo made a discovery
13:23which proved to be
13:24the first big advance
13:25in accurate timekeeping.
13:28As he watched a swinging lamp
13:30suspended by a long chain
13:32in the Cathedral of Pisa,
13:34he noticed,
13:34by counting his pulse beats,
13:36that each swing
13:37took the same time.
13:40So Galileo proposed
13:41using a pendulum
13:42as the basis for a clock.
13:44To keep the pendulum
13:46swinging steadily,
13:47the Dutch scientist,
13:49Christian Huygens,
13:50devised a mechanism
13:51inside a clock
13:52that gave the pendulum
13:54a little push
13:55at the end of each swing.
13:56This same mechanism
13:57also turned the hands
13:59on the clock face,
14:00counting the number of swings.
14:02It was the world's
14:04first pendulum clock.
14:05The grandfather of all
14:07grandfather clocks
14:08and the grandfather
14:10of all our best timing methods.
14:15For an order to measure time,
14:18you need something
14:19that will give you
14:20a constantly repeating movement,
14:23a rhythm,
14:24and then count the movements.
14:31The more precisely
14:32these movements
14:33repeat themselves,
14:35the more accurate
14:36your measurement of time.
14:42I don't care about
14:44bean plants,
14:45cockleburs,
14:45and pendulums.
14:46Where do we set the clock?
14:47The man in the observatory
14:49says we...
14:51I'll find out for myself
14:52what he says.
15:20Quite a piece of machinery,
15:22isn't it?
15:22Yes, it is.
15:28What is it?
15:30A hairspring
15:31and balance wheel
15:32of a watch
15:33in slow motion.
15:35Oh,
15:36a sort of portable pendulum.
15:38Real pendulums
15:40work only
15:40when they hang
15:41straight down,
15:42so they're no good
15:43for watches
15:43or portable clocks.
15:45But this mechanism
15:46gives a constant rhythm
15:47in any position.
15:53At each turn
15:54of the balance wheel,
15:55the escapement mechanism
15:57releases the locking
15:58of an escapement lever,
16:00ticking off
16:01the constant rhythm
16:02you need
16:03to measure time.
16:04The first watches
16:06were pretty,
16:07but not very accurate.
16:13Then, as the old world
16:16began to expand
16:17across the seas,
16:18accurate timekeeping
16:19became really important.
16:22You see,
16:23without accurate timepieces,
16:25navigation was a problem.
16:28I just checked
16:29the sun's position
16:30and found out
16:31that it's 12 o'clock here.
16:33By this watch
16:33I've carried
16:34ever since we left
16:35England a month ago,
16:36it's 9 o'clock
16:37in Greenwich.
16:38So,
16:39our position is
16:41three hours
16:42or 45 degrees
16:43east of Greenwich.
16:45Where does that put us?
16:47Uh,
16:48in Baghdad, sir.
16:50Baghdad?
16:55Watches just
16:56weren't accurate enough
16:57to keep exact
16:58Greenwich time
16:59on a long voyage.
17:01In 1761,
17:03after years
17:04of experimenting,
17:05an English clockmaker,
17:07John Harrison,
17:08developed the first
17:09really accurate
17:10portable timekeeper.
17:12It was off
17:13less than two minutes
17:14after a five-month's voyage.
17:17The accuracy
17:18of the ship's clock
17:19or chronometers
17:20as it's now called
17:21enabled man
17:22to navigate any waters
17:24and encouraged sailors
17:25to explore the seas
17:27all over the Earth.
17:29Although now
17:30ships can get
17:31Greenwich time
17:32by radio,
17:33all navigation today
17:34still depends on
17:36knowing what time it is.
17:38Well, now,
17:39that's the same problem
17:40we're having,
17:41knowing what time it is.
17:44I don't suppose
17:45you'd care to explain
17:46how they set their clocks.
17:47On Earth?
17:48I'd be delighted.
17:49Oh, good.
17:51All clocks are set
17:52by radio signals.
17:54In the Western Hemisphere,
17:55these come from
17:56the United States
17:57Naval Observatory,
17:59where signals are broadcast
18:00accurate to within
18:02one thousandth of a second.
18:13from such radio signals
18:15broadcast from
18:16various observatories,
18:18the clocks of the world
18:19are set.
18:21But where do the radio signals
18:23get their time from?
18:24From the official timekeepers.
18:27Special clocks
18:28regulated by quartz crystals.
18:31Quartz crystals?
18:32Well, what's wrong
18:34with pendulums
18:35and those other things?
18:38Balance wheels,
18:39they aren't accurate enough.
18:41They're rates affected
18:43by wear,
18:44movement,
18:45air currents,
18:46and temperature.
18:49Quartz crystals
18:50are less subject
18:51to these influences,
18:53but they give us
18:54repetitive movement,
18:56just like the pendulum
18:57and the rotating balance wheel.
18:59To the eye,
19:00quartz crystals
19:01seem inert,
19:02but actually,
19:03under the influence
19:04of an electric current,
19:06they vibrate,
19:07measuring off tiny
19:08and precise slices of time.
19:11These vibrations
19:12are added up
19:13by electronic circuits
19:14into seconds,
19:15minutes,
19:16and hours.
19:17Some quartz crystal clocks
19:19have a maximum error
19:20of one one-hundred-thousandth
19:22of a second per day.
19:25Well,
19:26that's certainly accurate,
19:28but if clocks
19:30are set by radio signals,
19:31and radio signals
19:32are set by quartz crystal clocks,
19:35how do they set
19:36the quartz crystal clocks?
19:37By the master clock,
19:39which is the turning
19:40Earth itself.
19:42Every night,
19:43when the sky is clear,
19:45United States Naval Observatory
19:46astronomers photograph stars
19:48through a fixed vertical telescope.
19:51From this,
19:51they determine
19:51the precise instant
19:53when the observatory
19:54passes directly
19:55under a particular star.
19:58The next night,
19:59they note again
20:00what time they pass
20:01under that particular star.
20:11The positions
20:12of the multiple exposures
20:13on the star plate
20:14are then carefully
20:15and accurately measured.
20:20The information
20:21is turned over
20:22to the electronic calculator
20:28and the result
20:29is the true
20:30determination of time.
20:34Based on these readings,
20:36they're able to find
20:37the precise time
20:38that it takes the Earth
20:39to make one rotation.
20:43The official clocks
20:44are compared to this
20:45and their rates
20:46are calibrated.
20:49Come in.
20:53Excuse me, sir.
20:54I was just wondering...
20:55Ah, you're just in time.
21:00I have come to a decision.
21:02We'll set our clock
21:03by the Earth.
21:04The perfect timekeeper.
21:07Well, not perfect.
21:10What do you mean by that?
21:11The Earth is gradually
21:12running down.
21:14Running down?
21:16I refuse to accept that.
21:19But it's true.
21:20Friction is the main force
21:22that's slowing down the Earth.
21:24Where does the Earth
21:25get its friction?
21:26from tides.
21:31These tidal bores
21:32in the Bay of Fundy
21:33are good examples.
21:36Friction from tides
21:38in the shallower seas
21:39is gradually
21:40slowing down the Earth.
21:44Slowing down?
21:46If we can't trust the Earth,
21:48what can we trust?
21:50Well, the scientists themselves
21:51are not satisfied
21:52with the Earth as a clock.
21:54Now they're working
21:55on an atomic clock.
21:57A clock based on
21:58the cesium atom
21:59has been developed
22:00at the National Bureau
22:01of Standards
22:02in Boulder, Colorado.
22:04This clock keeps time
22:05by counting motions
22:07inside the atom.
22:09As the nucleus spins,
22:11its axis swings
22:12back and forth,
22:13and the swings
22:14are detected electrically
22:16and counted.
22:17The motions of atoms
22:18are more regular
22:19than those of pendulums,
22:21balance wheels,
22:22the Earth,
22:24and even of quartz crystals.
22:26And it's likely
22:27their regularity
22:28will continue
22:29as long as matter exists.
22:31This clock is believed
22:32to have a maximum error
22:34of one second
22:35in 3,000 years.
22:37Well, that's accuracy.
22:40Sir, it occurs to me...
22:42Yes?
22:43Well, I don't think
22:44it would make much difference
22:45to anybody
22:45if they did lose
22:46a second or two
22:47now and then.
22:48Well, everyone depends
22:49on accurate timing
22:51whether they're aware
22:52of it or not.
22:53For example,
22:56with quartz crystals,
22:57it's the precisely
22:59controlled number
23:00of vibrations per second
23:01that determines
23:02the kilocycle
23:03and megacycle channels
23:05used in broadcasting,
23:08television,
23:11and multiplex
23:12where many messages
23:14travel a single cable
23:15or travel a radio relay beam.
23:19Accurate timing
23:21of electrical impulses
23:23is the heart
23:24of all communication systems.
23:27And even greater accuracy
23:29and timing
23:29is needed by scientists
23:31who are constantly
23:32trying to get
23:33a more complete
23:34and accurate understanding
23:35of the physical universe.
23:37And today,
23:38the quantity
23:39that can be measured
23:40more accurately
23:41than anything else
23:42is time.
23:43Well, I suppose
23:44such accuracy
23:45is important
23:46to a scientist
23:47and engineers.
23:48But still,
23:50one little second
23:51doesn't seem
23:52so important.
23:53Really?
23:54Oh, a second
23:55is important.
23:57Take a look.
24:04Nine and three-tenths seconds.
24:07What kind of a clock
24:08was that?
24:09A stopwatch.
24:10It measures intervals
24:12of time
24:12down to
24:13a tenth of a second.
24:15Of course,
24:16it's not very practical
24:17when you're trying
24:18to measure
24:18a millionth of a second.
24:21But who'd want
24:22to measure
24:22a millionth of a second?
24:25Scientists,
24:26engineers,
24:26technicians,
24:28anyone who deals
24:29with things
24:29moving at high speed.
24:31What kind of a clock
24:32would they use for that?
24:33Usually a cathode ray
24:36oscilloscope.
24:37Never heard of it.
24:39Basically,
24:40it's much like
24:41a TV picture tube,
24:42but it's used differently.
24:44The beam of electrons
24:46sweeps across the screen
24:48over and over again
24:49in the same track.
24:53Now if we connect,
24:54say,
24:55a microphone,
24:56sound will jog
24:57the beam
24:58and make it jog
24:59in the trace
25:00like this.
25:03The ticks of a watch
25:04put time markers
25:06on the sweep
25:07five to the second.
25:14When we speed up
25:15the sweep,
25:16the time between ticks
25:17is stretched out
25:18to full screen.
25:23Speeding up the sweep
25:24still more
25:25and using
25:26an electronic timer,
25:27we can put on
25:29markers of
25:29a hundredth
25:30of a second
25:31or less
25:33and measure
25:34the speed
25:35of a bullet
25:36as it cuts
25:36two wires
25:37only a foot apart.
25:44Let's take another look
25:45and stop the picture.
25:48The interval
25:48between the two
25:49vertical lines
25:50we've drawn here
25:51represents the time
25:52it took for the bullet
25:53to break the two wires.
25:56How long was that?
25:58A thousandth
25:58of a second.
25:59That's really
26:00quite a long time.
26:02A radar scope
26:04with even faster sweeps
26:05tells how long
26:07it takes for a radar signal
26:08to strike an object
26:09and bounce back.
26:10That tells you
26:11your distance
26:12from the object.
26:13Or,
26:14you can time signals
26:15from three
26:16Loran stations
26:17operated by
26:19the United States
26:19Coast Guard
26:20and by comparing them,
26:23adjusting the traces
26:24so they will coincide,
26:27know your exact position.
26:31by putting markers
26:33on a very fast sweep,
26:35scientists find it easy
26:36to measure intervals
26:37of a billionth
26:38of a second.
26:39Well,
26:40that's not too bad,
26:41is it?
26:42Do you have any idea
26:43how short a time
26:44that is?
26:45Do you?
26:48Frankly,
26:49I don't.
26:50Well,
26:50a billionth
26:51of a second
26:52has the same
26:53relationship
26:54to one second
26:54as one second
26:56has to 35 years.
26:59One second
27:00to 35 years?
27:03Yes.
27:05Now I see
27:06how small
27:07that figure is.
27:08And even a billionth
27:09of a second
27:10is long
27:10compared to
27:11the much shorter
27:12times that scientists
27:13have to deal with.
27:16although the atomic world
27:17that makes up
27:18this drop of water
27:19is still hidden
27:20from the eyes of man,
27:22we know a good deal
27:23about how these bits
27:24of matter behave,
27:26how they move,
27:27and in how short a time.
27:30In this drop of water,
27:32there's a vast number
27:33of atoms
27:34in constant motion,
27:35and just one
27:36of these atoms
27:37will have
27:3810,000 collisions
27:40in a billionth
27:41of a second.
27:42and in the time
27:43between each
27:44of these collisions,
27:46the outside electrons
27:47of the atoms
27:48would go around
27:49100 times.
27:52And in the time
27:53it takes
27:53an outside electron
27:54to go around
27:55just once,
27:56the inside electrons
27:58would go around
28:00100 times.
28:01And in the time
28:02it takes
28:03the inside electron
28:04to go around
28:05just once,
28:06the particles
28:07in the nucleus
28:08of the atom
28:09would vibrate
28:10100,000 times.
28:12these are
28:14the tiny intervals
28:15that scientists
28:16must try to measure.
28:21to go around
28:37and see you
28:37in the future.
28:37Obrigado.
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