Friday's Physical Law - Conservation of Momentum

Well all have experience Newton's Third Law of Motion in action, every time we push on something like a door we can feel it pushing back on us.

What we have here is action and reaction, and as it is normally put Newton's third law reads every action has an equal and opposite reaction. So if I push the door with a force of 5 N the door pushes back with the same force.

Of course the main thing to note about these forces is that they operate on different objects. Many people seem to get this confused by thinking that the forces cancel out, which can only happen when forces are acting on the same object, which is not the case here. To use my previous example: I push on the wall and the wall pushes back on me.

Of course the action and reaction occur at the same time, they start at the same time and they finish at the same time. So this gives us another measure of the motion that results from these forces. Remember that as we saw a couple of weeks ago

• F = ma,

and since we know the force applied in the action and reaction and the mass of each object and now the time over which the force acts we can work out the change in velocity (remember that a = v/t). So this gives us what we refer to as impulse:

• F t = mΔv = Δp

What we have here is another measure of motion, momentum (p) which is equal to an objects mass times its velocity. And from Newton's third law we see that when ever we have to objects interacting (action and reaction) then their is a change in momentum is equal (and opposite). That is the total (nett) momentum of two interacting objects is conserved (the same before and after the interaction).

As we progress through this series we will see many more examples of the idea of conservation of quantities. But in this case we have a very good means to analyse the interaction of objects (the idea of two objects interacting can be extended to multiple objects where momentum will still be conserved) such as in collisions.

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How to ... sweep almost all science under the rug

In the "culture wars" with ID (intelligent design) I have always found it amusing at the big tent attempts of the IDists to encompass such a wide range of creationists into their folds.

We know that all creationists try to sweep good science under the rug by ignoring, denying or misrepresenting it, mostly in biology and related fields such as anthropology and palaeontology. But some take their anti-science to greater and greater heights, particularly YEC (young Earth creationists) who manage to be not just anti-evolution but anti-every-thing-else-in-science as well.

The YEC seems to be the most vocal proponents of ID, but why then are other groups such as OEC (old Earth creationists) backing the completely anti-science stance of YEC when they are more intellectually consistent with the rest of us?

This is something that I cannot answer, maybe some one else can for me, but what I want to look at here is just what science exactly does the YEC position deny? (WARNING: this could be a very long list) In brackets I have listed some examples of our understanding of which exactly is undermined by YEC. The ones with * are also in common with all IDists.

1. Microbiology* (antibiotic resistance)
2. Botany* (breeding plants)
3. Zoology* (breeding animals)
4. Ecology* (co-evolution of plants and animals)
5. Biochemistry* (protein synthesis)
6. Medicine* (Germ theory of Disease)
7. Anthropology* (Descent of Man)
8. Palaeontology* (fossil records) - Note that YEC also has issues with the dates of fossils
9. Chemistry/Atomic Physics* (cause of mutations in DNA and hence their effect)
10. Nuclear Physics (radiometric dating)
11. Cosmology (age of the universe)
12. Particle physics (since it goes hand in hand with cosmology)
13. Geology (formation of rocks and fossils)
14. Tectonics (the movement of tectonic plates)
15. Physical Geography (the shape of the land)

Hmmmm well I think my list is not as long as I thought it was going to be, but then again I think that I have pretty much covered the whole spectrum. And if I have forgotten anyone's speciality please tell me. I also realise that I could have made this list longer by including more specialities that I have lumped into generalities (eg medicine). And while the list is longer in the section that is ID general rather than YEC specific those YEC specific areas are rather broad.

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Psychics are bad for you

For all those who are fans of psychics maybe you have found the wrong blog to be reading.

The Amazing Randi has updated the terms of his paranormal challenge, in which if you can prove you have paranormal powers in a mutually acceptable test then you walk home with $1,000,000. Now instead of merely waiting for applicants they will go out and target high profile paranormalists, taking the challenge to them.

Several notable psychics have said they will take the challenge only to back down, one major example of this Sylvia Browne, and there is now an online petition that you can sign to urge her to step to the plate

You can read more about all this here where Skeptico gives us a good run down.

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OV-102, may she rest in peace

And from the I can't believe I nearly forgot to post about it files comes some thing that is very dear to me.

February 1 2003 (Thursday was the 4th aniversary) the space shuttle Columbia broke up on re-entry killing all seven astronauts aboard.

I have always felt a special bond with the space race and Columbia in particular since my birthday falls on Cosmonaut's Day (April 12), which is the anniversary of the first manned space mission Vostok 1 (1961) in which Yuri Gagarin became the first man in space. And what does that have to do with Columbia, on the 2oth aniversary of Vostok 1, STS-1 the first orbital test flight of the space shuttle was launched. So Columbia (OV-102) with two people on board was launched on my first birthday (1981). Of course I was only one and didn't really register such things, but looking back on it well I thought it was cool and special (ok I really am a nerd aren't I - but is that really such a bad thing) and that Columbia was my shuttle.

Also the STS107 mission was a science mission and one of the experiments was using the Isreali Dust storms Experiment camera to try to take picture of Red Sprites (to put it simply a form of upwards lightning) and to help orient themselves on the storms the made use of the World Wide Lightning Location Network (WWLLN - pronounced "woollen" as in made of wool) which was started by a now retired member of my research group and is a project that we are still much involved in. So I hade multiple connections to this tragedy

So like I mentioned February 1 she broke up on re-entry, killing all seven of the crew, so if we could take a moment to remember Brown, Husband, Clark, Chawla, Anderson, McCool, Ramon. And please give me a moment to mourn my shuttle.

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Friday's Physical Law - Reflections

In the first two weeks of this series I started out with simple motion as my fundamentals and then built from there, and I do intend to continue in that vein but every now and then I am going to feel like something different and this week is one of those times.

Today I am going to discussing some thing that is part of my PhD research and is also something that merits a comment when talking about Climate change. That is reflection.

To begin with we must have a wave travelling along that interacts with an object (or the boundary between two media - ie water and air). Now when this wave (and for the most part I will be dealing with electromagnetic (EM) waves such as light, radio waves etc., although this applies to all types of waves) interacts with an object any of three things can happen:

1. Reflection
2. Transmission
3. Absorption.

Which of these occurs depends on the properties of the object and the wave. And in most cases two or even three of these things happen together.

Reflection is where the light strikes the object and bounces off. Transmission is where the light passes through the object. Absorption is where the light is ... well ... absorbed.

If we start of with a wave intensity of 1 then:

• R + T + A = 1

where R, T, and A are the amounts of the wave reflected, transmitted and absorbed respectively.

The obvious examples are a mirror for reflection, a window for transmission, and a black object for absorption.

And you will notice that I mentioned a colour specifically for the absorption, in fact it is due to reflection and absorption that we see colour. Light shines on an object and if red light is reflected and the green and blue light absorbed then we see the object as being red.

Now what does all this have to do with my research, well, I study the electrical interactions of the upper atmosphere (more about this another time) and the main tool we use is by using the ionosphere and ground as a mirror (albeit and imperfect ones) and sending radio waves long distances between these two "surfaces" and so the reflective properties of particularly the ionosphere are very important. And by looking at the changes in the signals we receive we can determine the changes in the reflections along the way and hence the local (or global) changes that has caused them.

And of course I also mentioned that reflections can affect climate change, if you have snow, ice or tundra then the sunlight reflects of this quite well, as any one who has gone skiing can attest to. But as these melt less of the sunlight is reflected and hence more is absorbed (since the Earth is not very transparent). This leads to more heat being trapped in the Earth-atmosphere system leading to more warming (even if only locally) which will lead to more melting which will lead to more absorption and so on. In other words it is a positive feedback loop for the warming which is not a good thing, especially since we can quite easily measure the amount of ground covered by snow, ice and tundra and it is decreasing.

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How to... yo yo diet

If you are at all conscious about your body, and lets face it most of us are (not as much with the guys but still), then at one point or another we have been at least tempted to try some sort of fad diet.

The idea behind most of these (apart from making lots of money for their creators) is that be eating only certain things (ie no carbs, or no fats) or eating in certain ways (only raw food) or by substituting "supplement shakes" for meals one can lose weight.

Of course there is one other method by which people often try to lose weight and that is simply by starving themselves. And it is this rather than the others that I want to focus on today.

Our bodies are wonderful mechanism - in times of plenty we store the food for times where food is rather scarce, however one other thing is that in times of scarcity our bodies will also slowdown so that the stores we have can be made to last as long as possible, this is especially useful if you do not know when more food will be available again.

So what happens when you try to lose weight by cutting calories alone:

1. Your body thinks (rightly) that it is a time of scarcity of food
2. So your metabolism slows down to conserve your food stores -fats, glycogen (stored carbs) and protein
3. Since you are still not taking in enough food to subsist, even with the reduced metabolism you body starts to burn its stores.
4. Your body is used to operating mainly of carbohydrates since these are the easiest to use so you store of these, glycogen, is used first.
5. This leads to a quick loss of a couple of kilos since the break down of glycogen releases a lot of water.
6. Once the glycogen is used up the weight loss slows, and the body now must turn to an alternate fuel.
7. The blood-brain barrier is impermeable to fats, so either that stored fats have to be broken down (a difficult task) or instead protein can be used (what actually tends to happen)
8. The primary weight loss now is muscle wastage as the proteins from the muscles are used in respiration (which is the process of releasing stored energy not the process of breathing in and out, which is a small part of the former).
9. If this continues for some time important muscles such as the heart can begin to degrade, which as you can imagine causes no end of life threatening problems.
10. If at some point you do stop fasting, you body suddenly goes into "time of plenty" mode (which it is at least relative to the fasting) in which the main aim is to restore the used body stores of energy (and of which fat is the most efficient).

Now some people go through this process and are quite pleased with their weight loss, which is why the get to step 10, unfortunately this leads them to put on weight and quite often this is more than they lost so they start again. So it becomes a bit of "Lather, Rinse, Repeat"and of course this can go on and on and on ... Hence the "yo-yo diet" moniker.

Of course the observant of you will have noted that no where did I mention using the stored fats, this is where exercise comes in to the equation, you can only burn fat through prolonged aerobic exercise - ie long and relatively slow (and steady) exercise such as jogging, swimming, and walking that sort of thing

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Fridays Physical Law - Force and Accelleration

As we saw last week a change in motion of an object requires a force to act on the object. Of course with change in motion we mean that an object can speed up or slow down or simply change the direction of motion - all of these acts are covered by the term acceleration.

Technically acceleration is the rate at which the motion changes, or the change in motion divided by the time it takes for the change. So like velocity is how fast you are moving (changing position) acceleration is how fast you are changing your motion (velocity).

So when ever we have a force acting on an object we get an acceleration. Of course multiple forces causing multiple accelerations could also be acting to reinforce or cancel out each other. Two people pushing a car (from the same end) make it twice as easy to get going, whereas if one was pushing forwards and the other pushing equally backwards then these would cancel out.

If we increase the force then we increase the acceleration, but what else effects this relationship? The answer to that is mass, the heavier an object the more force is required to get the same acceleration as a lighter object. This is described in Newton's Second Law F = ma.

A force in the direction of motion increases the speed, and a force counter to the direction of motion will decrease the speed. A force at an angle to the motion will cause a change in direction of motion as well as an increase/decrease in speed.

We also have the interesting case of a force at right angles to the motion, this will not cause any change in speed only in direction. And if this force is always at right angles to the motion then the object will continue at a constant speed the changes in direction will cause it to move in a circle. In this case we call the force a centripetal force, meaning center-seeking, but more about that another time.

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How to ... Get cancer from a Cellphone

The energy in individual RF (radio frequency) photons (individual photons interact with individual electrons in atoms) is far to little to cause ionisation (when the electron is completely removed from the atom) or any other known mechanism for causing cancer. So if you want to get cancer from your mobile phone or your wifi network or your microwave (outside of 24/7 use) I will outline a method as follows

1. Take your favourite RF device
2. Open up the device and remove the circuitry
3. Depending on the method of oscillation, you will need to alter the capacitance/inductance or the resistance of the oscillator circuit, or by reprogramming the chip.
4. The frequency of oscillation was probably in the range of 10 - 1000 MHz (million of cycles per seconds) this will need to be increased to 100-1000 THz (million million cycles per second) ie from radio/microwaves to visible light.
   
5. This causes an increase of photon energy by a factor of 10 million or so, enough to now ionise some matter and hence be a possible cause for cancer.
6. Put device back together and turn on.
   

OK so a lot of people have concerns about RF radiation, for the most part these fears are unfounded in science, however this does not affect those that are worried. Of course this is not mean that a mechanism may be found in which this frequencies could have a detrimental effect outside of heating.

On the note of heating, as long as the RF radiation is not continuous (ie you have breaks from having you cell phone next to you ear) then the heat rapidly dissipates and is not an issue.

If anyone wants more information about recommended limits that were discussed at the last International Union of Radio Science (URSI) General Assembly, I can provide links to abstracts etc. It was actually a very food and informative session.

Also I would like to thank Jennifer Oullette of Cocktail Party Physics for the inspiration

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Please, Your Tshirt is a Security Threat

A passenger has been barred from an International flight from Melbourne to London for wearing a tshirt which calls Bush "The worlds #1 Terrorist" on the basis that the T-shirt could have upset other passengers.

And to make matters worse:

Qantas issued a statement saying comments made verbally or on a T-shirt which had the potential to offend other travelers or threaten the security of aircraft "will not be tolerated."

Now how on Earth does this threaten the security of the aircraft? Is the Tshirt going to spontaneously combust in mid-air?

Still it is good to know that America's allies are standing proudly along side the USA as they fight the "War on Liberty" all over the globe.

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Schrodinger's Cat

Ok the other day I was standing in the kitchen cooking dinner for the family and looking out the window I could see our cat lying on the concrete by the washing line, and then looking again i could see another very similar cat lying on top of the compost bin. Looking closely I could not make out any differences between them, nor on either cat could I see our cats bright yellow refelective collar (which proves very usefull on an all black cat at night).

To this day I have never seen another lithe black cat in the neighbourhood, and our cat has never been what you would call friendly to other cats (many late night fights are started below our bedroom window).

My wife went down to see the cats and by the time she had gone down the stairs to the yard the cat by the washing line had disappeared and our cat was lying relaxed on the compost bin.

Maybe what I was seeing was the famous Schrodinger's cat, well not exactly (since that had to do with whether the cat in the box was alive or not) but certainly the parallels to quantum mechanics are abound.

Obviously the "catfunction" was a superposition of two states and when my wife went out to make an "observation" the catfunction collapsed to the compost bin state.

Maybe? Or could it be something else?

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