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Name:: The Boy With No Lab Book
Question: IM THINKING PHYSICS THINGS!!!! :-O
right....
beside me is a box-on-wheels type thingy which is hollow...
ontop of it is my external HDD and a pint of water...
when the glass is ontop, no noise can be heard...
when the glass is removed, the HDD is VERY noisey...
if the glass is replaced by any other object it is still very loud...
(apart from a bottle of Dr Pepper, which makes the noise slightly quiter but not
much...)
therefore i have come to the conclusion that the water must be magic.
please prove me wrong using lots
of big physics words.
thank you
I can't resist the challenge to prove you wrong so here goes...
The HDD is very noisy I'm guessing due to excessive vibrations within the casing, this is probably due to an imbalance
in one of the motor parts of the HDD - probably something has fallen off and made it so. When objects vibrate at their natural
frequency resonance occurs - which means that the amplitude of vibrations (loudness in this case) can be very large. To reduce
the amplitude of vibrations, damping needs to occur, so that the energy of the vibrations is dissipated. In your case, a pint
of water will absorb the vibrations and the energy is dissipated in moving the water around the glass. Dr Pepper will accomplish
the same thing but as there's less liquid it won't do such a great job. Also, as it isn't as heavy as the pint of water, it
won't press down onto the HDD as well and less contact is made so less energy is absorbed and dissipated. To prove that the
water isn't magic - because you can never prove that it is, only that it isn't (check out Popper's ideas about falsification)
you could perform the same experiment with different liquids. First, do it with ice to prove that the water isn't magic, then
try milk perhaps and so on.
Proven wrong? You need to do more experiments I think, shame you've lost your lab book!
Question: Hi sir!!! got a question 4 u!! (even tho i have abandoned u 2 go
in2 the navy, i still use this
as revision 4 my AS Physics) theres an ongoing
argument at college that if there were two black holes equidistant from
the Earth, would the earth split into 2 or stay put? And none of the physics teachers (in all their wisdom) have given a definate
answer
Ta
Suzy (PS say hi 2 every1 from me!)
Hi Suzy,
I've done some sums and here are my thoughts:
Say, for the sake of argument, that the Sun suddenly
became a black hole
because it collapsed in on itself. It would have an event horizon of 2950m
which means anything
within this limit would be stretched to an incredibly
long length and then "sucked" into the black hole forever. Clearly,
this
radius is very small and so not even Mercury would be within this limit.
The gravitational field strength on
the Earth due to the Sun is 0.00640N/kg
whether it is the Sun or a black hole. (Note the gravitational field
strength
at the Earth's surface due to the Earth's gravity is 9.81N/kg)
For one black hole:
We are unlikely to notice
the gravitational pull of the Sun/Black hole
unless it is comparative to Earth's so dividing 9.81 by 0.00640 we get
1533,
which is how many times more massive the Sun needs to be to have a
gravitational field strength the same as Earth's at
the Sun's current distance from us.
One would notice this if there was one black hole as it would mean that
when
you were facing the black hole (day-time - not that you could see it)
you would tend to float and when you were not facing
the black hole
(night-time) you would tend to be somewhat heavier - an understatement
perhaps!
For two black-holes:
Assuming
these are two identical black holes both with a mass 1533 times greaterthan the Sun, I suppose that you would tend to
float when you are facing either of the black holes and tend to be on the ground when at 90 degrees
to the black holes.
Certainly,
with 2 black holes a lot of destruction would occur as everything that is not fixed to a surface would tend to move around
- people, animals, cars, boats, etc.
In answer to your initial question, would the Earth be pulled apart?
Unlikely,
unless the event horizon was very close to the Earth itself.
Could we live on a planet that had two black holes positioned
as I
describe above - probably not.
I hope this answers your question. There are just so many variables to
consider
that unless we are very specific, an answer just doesn't exist!
In the Seebeck effect, thermo emf rises as the temperature of the hot junction is increased, keeping the cold
junction at a constant temperature. But the thermo-emf increases to a maximum value only: then it falls gradually to zero;
and it reverses. What is the mechanism behind this?
As I understand it, the voltage between the junctions depends on the Seebeck coefficients of the two materials and the
temperature difference between them, such that V = (S2-S1)x(T2-T1). As long as the Seebeck coefficients are constant for that
range of temperatures then so will the voltage.
If you are using a ballistic galvanometer to observe the Seebeck effect it is possible that the sensitivity is set to
too fine a setting and the indicator overshoots and then correct itself which might look like it has returned to zero.
Hope this helps.
How do you know if light is refracting towards or away from the
normal?
When you shine a ray of light at a 90 degree angle to a mirror it is reflected back along its original course - this
is the "normal".
Light travels fastest through less dense transparent materials. A simple analogy considers a car on a road travelling
fast (less dense material) which ventures onto muddy ground (more dense material) the front wheel first in contact with the
mud slows down causing a swerving action to the car - causing it to swerve towards the normal. The opposite happens going
from mud to road (the car's wheel speeds up when it encounters the road) and the car swerves away from the normal.
A similar situation can be considered with a sledge in the snow.
How does tranparency work at an atomic level and how the atoms of a glass behave when light passes through
it?
Good
Question! This is one of those areas that isn't usually included in textbooks as it is difficult to explain. My answer here
is the explanation with which I am most happy - not one that I profess to be an expert on!
Firstly,
light is neither a particle nor a wave. It is convenient to explain its behaviour in some situations as particle-like (photoelectric
effect) and sometimes as wave-like (diffraction). This is not a trick of physicists but an attempt to explain something that
we don't fully understand. Explaining the universe relies on real-life examples that may include analogies with projectiles
to explain particle physics and analogies with phenomena like water waves to explain wave mechanics, but neither
is fully correct.
A photon
that hits an opaque material is absorbed and the material heats up, resulting in the emission of lower frequency (less energy)
infra-red photons. If the material is transparent, the light passes through it, but not necessarily unchanged. Light slows
down in glass, for example, which means that the wavelength of the light is shorter because c = fλ. The photon’s
characteristics are the same as E=hf and the frequency hasn’t changed. This means that it is the same photon and that
it has passed through the material without being absorbed.
Photons
are absorbed only when the energy they possess matches exactly the difference between two electron energy levels. If it doesn’t
match this it is not absorbed. Glass, I assume doesn’t have energy levels that have differences equal to the energy
possessed by visible light photons. Remember that some electromagnetic radiation may be transmitted through some materials
and not others. Radio waves, for example, are reflected by the ionosphere but travel through glass. UV waves, for example,
travel through air but not through glass.
How do clouds float? As water is less dense than air and it's colder further
from the ground, so it can't still be in steam form, so how do they stay in the sky and be able to be blown around?
I think your answer contains an incorrect assumption, but also the answer to your question! Water evaporates at temperatures
lower than 100 degrees celsius because individual water molecules are at temperatures of 100 degrees celsius even though the
average temperature is probably a lot lower.
The water molecules rise as they are less dense than the surrounding air and will continue to rise as long as this is
the case. The water molecules will reach a point where they are cool enough to return to the liquid phase (or state)
and as you correctly state, at this point they are more dense than the surrounding air so will fall.
However, clouds are basically large volumes of water droplets that move around a common centre due to turbulence. Turbulence is
caused by pressure differences due to uneven solar heating of the atmosphere and the Earth's rotation.
Some water droplets in clouds are falling for a time, but rise again due to turbulence and this repeats as long as the
turbulence persists. If turbulence stops, the droplets fall as rain. The size of the droplets depends on how many cycles of
rising and falling within the cloud that the drops have undergone.
If the temperature is cold enough, the droplets freeze and fall as hail. The size of a hailstone is affected in
the same way - cases have been reported where the hail is as big as footballs!
If a fly hits a train head-on, the fly stops for an instant as it is slowed down. Is it true then that the train
stops too?
This would be true if the whole of the fly did stop for an instant - the train would also have to be stationary for an
instant. People inside the train would certainly notice this happening though, so something must be wrong with this idea.
The problem with this example is that the front of the fly impacts with the train, slows down, stops and then speeds
up in the opposite direction - while the rear of the fly is still moving towards the train - this is why flies go splat!
If it was a bullet instead of a fly it seems a bit more believeable, but for the bullet to stop the train it would also
need to be incompressible. The front of the train would also need to be incompressible, the bullet could not deflect from
the front of the train and must only adhere to the train's front!
All of which takes some of the fun out of the idea, but the problems it leaves are still present and the whole problem
becomes an unphysical one. An idea that is theoretically possible, but could never work in practice! Sorry.
Am I the one and only? from Chesney Hawkes
Strictly speaking, the one and only implies that you are fundamental, when most people know that the human body consists
of smaller units called atoms. Smaller than atoms are protons and neutrons and these consist of quarks, namely up and down
ones in different combinations. Everyone is made of up and down quarks, so you are not in fact, the one and only!
In the film "2001: A Space Odyssey", an astronaut finds himself locked out
of his ship (The Discovery) in
his little pod (Anna). Foolishly on the way out he left his helmet behind and so he is only wearing the remainder of his space-suit.
the entire crew (bar himself) were killed for reasons which are complicated. To get back in he uses the pod's servo arm to
open the emergancy airlock, and then uses the eject function of the pod (after careful maneuvering) to throw himself into
the airlock where he seals the door and floods the airlock with oxygen before retrieving a spare helmet and advancing into
the ship to shut down the psychotic ship's computer (HAL-9000 series). This begs the question: how long can a human survive
in space without a space-suit?
Current research using barometric chambers suggests that you would remain conscious for about 10 seconds, but would
die after about 90 seconds. The problem has to do with lack of pressure rather than lack of air. On Earth our skin is subjected
to 100,000N/m2 of pressure due to the atmosphere and our body is perfectly adapted to this. As pressure decreases the force/unit
area on our skin gets less and the blood (amongst other fluids) in your body expands. On Everest water boils at about 72
degrees Celsius due to the reduction in pressure and the same will happen in your body except that in a vacuum there is effectively
no pressure at all so your blood in your veins will boil!
If you were unfortunate enough to be confronted by such a situation, the worst thing to do would be to hold your breath.
This would cause your lungs to rupture as the pressure in your body attempts to become equal with the external pressure (which
would be incredibly painful ).
What is the composition of light particles in a rainbow?
A light particle is usually described as a photon, a wave packet, of fixed frequency that gives it a certain colour.
On the other hand, classical Physics would have us believe that light is a wave and that white light consists of 7 colours
(red, orange, yellow, green, blue, indigo and violet) that Isaac Newton came up with. Interestingly, Newton made up the fact
that there are 7 colours in a rainbow due to the mythical connotations of the number 7. There are, in fact, 6 colours - indigo
being the invented one!
The problem is in separating the particle nature of light from the wave nature of light and physicists have accomplished
this by suggesting that light is neither a particle nor a wave, but behaves like particles in some experiments (photoelectric
effect) and waves in others (refraction, diffraction, etc.).
More unusual, is de Broglie's assertion that while light can have particle and wave properties, so particles like electrons
can behave like waves provided with the right situation (electron diffraction).
It is commonly known that after being connected to mains voltage your muscles spasm and you go flying across
the room, is there a limit to how much voltage can be applied and also if someone was stood upright would it be possible to
make him jump super high?
You are quite right in that one possible effect of mains voltage is to cause a person to apparently go flying across
the room. However, it is more likely that the person remain in contact with the mains appliance because of something called
the "let-go current". This value is approx 15mA for a 70kg man and means that your muscles spasm so hard that you are unable
to let go.
For further info speak to my 11TS01 GCSE Science class of 2004-2005 for details of a mains voltage experiment involving
me that went wrong.
The resistance of the human body is very high and if you apply Ohm's Law (V=IR) you can calculate it if you assume that
230V provides at least the required 15mA (which I can assure you it does). There is no limit to the voltage that could be
applied, but the higher the voltage, the higher the current (assuming other factors are constant) and a current of 60mA is
sufficient to cause ventricular fibrillation which stops the heart from pumping blood. Contrary to what you see in films the
heart can't be started again unless another electric shock is provided by a defibrillator.
Ultimately, how far a person travels across a room depends on the strength of their muscular contraction as it is this
force that causes them to move. If you were able to control the contractions of enough muscles in the correct order you may
be able to jump as high as a high jumper for instance - but there are obviously limits - there is no way you could ever jump
to the scaled height that fleas and other insects jump to! Sorry.
Is the Wein's law Constant 0.0029 or 0.0029x10^-3, It's confusing because on the data sheet it is stated as 0.0029mK
(I presume the mk means millikelvin, which would mean diving the number by 1000).
Wien's constant is a physical constant that defines the relationship between the thermodynamic temperature of
a black body (an object that radiates electromagnetic energy perfectly) and the wavelength at which the intensity of the radiation
is the greatest. The Sun, for example, radiates most in the visible spectrum - it is no wonder then that most creatures on
Earth have developed eyes that respond to these wavelengths. It is equal to approximately 2.898 x 10-3 meter-kelvin
(mK). Constants are generally expressed as standard form using SI units so usually no prefixes like milli, for example.
The most notable exception is mass, where the SI unit is kilogram (kg).
From: A worried 6yr old
Question:
What speed should a solid object the size of a small child (6-7yrs old) be thrown at so that the travelling object
becomes 'completely' invisible to the human eye, even when it passes right in front of the person?
To pass in front of your eyes without you seeing a person would require quite a large speed. In tests with air force
pilots, the human eye was able to register the identity of an aircraft when it was flashed on a screen for 1/220th of a second!
That involved identifying the aircraft so you can safely assume that 1/300th of a second would be enought
time to register that something was there. I suggest that 1/500th of a second is a reasonably short enough time to say that
if someone noticed something, they wouldn't be sure that they had seen anything.
So, back to the initial question - how fast? If a person confined their vision to an area in front of them approx. 5m
across the person would need to traverse that distance in 1/500th of a second. Using speed = distance/time we arrive at an
answer of 2500m/s or 5625mph. The speed of sound is approx. 765mph so the person would need to be travelling at approx. 7.4
times the speed of sound!
At present no aeroplanes travel at this speed, but NASA are developing scramjets that should be capable of this immense
speed! Search their website for more info.
In response to the question about how long a human can survive in space without a space-suit, you said that the
major problem would not be lack of oxygen, but lack of pressure which would cause the blood in a persons body to boil.
However
in space, although the pressure is as close to zero as makes no difference, the temperature is also very close to zero
so makes no difference. So is there still enough heat to boil a person's blood (and other body fluids)? And if not, how long
could the person survive?
An explanation of why substances boil should clarify up this question. In solids there are strong intermolecular forces
that hold the structure together, in liquids these forces are very small and in gases they are negligible.
A solid object in outer space would remain in the solid phase (or state) due to these forces. A liquid, on the other
hand, does not have these forces to hold it together and on Earth is prevented from boiling (molecules escaping into the gaseous
phase) by the atmospheric pressure pushing down on the liquid.
This pressure isn't present in outer space and so without it any liquid will change into a gas regardless of the temperature
of that region of space - as long as it is above absolute zero - which it is anywhere in space (approx. 3K or -270 degrees
C).
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