You are quite a long way off with your estimate, though you're right that the effect would be small.
One mole of lead is 207 grams so the energy you are talking about would cause a 1 K rise in only (207 * 2 * 10^12) / (6.02 * 10^23) or 6.9 * 10^-10 grams of lead.
That's less than the mass of a human ovum. Orders of magnitude (mass)
And the heat capacity (by mass) of water is about 32 times that of lead so you could heat up even less than that - just over 2 * 10^-11 grams of water.
If someone drives an X-ray emitter past me they are going to find my boot up their ass.
Though the detectors are perfectly capable of detecting boots, due to the low penetrability of the electromagnetic waves I think you should be reassured your boot will remain well hidden.
Same reason everyone uses *zilla to describe something big. Its part of modern culture.
The use of *gate is so common now, perhaps the phenomenon should be called gatezilla.
Here's a better graph of sea ice. It's actually greater now than it has been than in the past 30 years.
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/global.daily.ice.area.withtrend.jpg
+1 informative for the posting the link, -1 interpretation for implying the opposite of what the graph shows.
I'm almost done reading them all!
That's my next challenge - once I've finished reading the web.
Actually, come to think of it, a well-trained dog is probably one of your better security options.
A well-trained dog would be good, but I reckon having an un-house-trained dog would deter most unwelcome visitors.
Why do conquerers conquer? Resources!
And to snuff out perceived current or future threats.
Given mans' penchant for war and the recent development of space travel, another race might have good reason for seeing us as a future threat, particularly if they think we're close to having the technology for developing WMADs (Weapons of Mass Alien Destruction).
More than likely, they would be explorers, observers, teachers, or all the above.
Or weapons inspectors?
Really? Because when I look around at everything around us, I see the evidence of such incredibly intricate and complex systems that I am further convinced in the existence of some kind of creator.
Intricate and complex systems often result from surprisingly simple causes e.g. iteration of z(n+1) = z(n) + c (where c is a complex number), gives rise to the Mandelbrot Set.
Carbon dating has been proved time and again an inaccurate measure of age so we can only theorize how old something really is (best educated guesstimate) unless there is very clear documentation as to the age.
Carbon dating is never used to data dinosaur fossils - its half-life is far too short. Other isotopes with much longer half lives are used to date rocks and fossils.
There's a good description of the science behind radiometric dating and some of the misconceptions regarding its accuracy here: Radiometric Dating - A Christian Perspective
These comments! There should be a Law.
Yes, a law administered by circuit judges.
In clarification, don't confuse work with energy. They aren't quite exactly the same thing. What is correct to say, is a force does no work if it does not cause a displacement of the object along the vector of the force. This says nothing about the expense of energy though other than to say, an appropriate amount of energy expended will accounted for in the work done. It does not mean that that is the only energy expense nor that for energy to be expended work must be done.
It's a long time since I was really up on physics and maths and I may have been imprecise with terminology etc. I agree that the vector components of the force need to be considered - particularly important for the string-rock system under discussion where the force on the rock along the tangent is 0, hence the KE does not change (assuming string is attached to a fixed point, frictionless system etc). I'm not sure I understand your last sentence - are you thinking about systems with friction etc?
I've enjoyed reading these posts - it's good to get back up to speed with some of the basic concepts I used to be familiar with as a student. I've found a couple of the links here useful.
Yes you will have burned calories but you will have done no work on the wall. The work performed will have been within your body caused by the contraction of muscles. The energy expended will have been converted to heat, presumably now lost to the environment through your skin if you're still alive
If you want to consider all forces and energy transfers within a human body when pushing against a wall, there's a lot to consider - it's far simpler to assume the body is rigid and has no internal structure that you need to be concerned about - in your example perhaps think of a rigid body leaning against a wall, which will impart a force but does not expend energy. In this case we would only need to consider mechanical properties of the system rather than the thermodynamic properties that apply to all real-world systems.
Of course if you are a biologist it might be valid to look at the the energy expended pushing against a stationary wall for an hour. In this case they might want to consider the the source of the energy (chemical), how forces act on the skeleton, the mass of limbs etc - not very useful though if you want to understand fundamental concepts of physics.
Reading through the discussion above and below, it's clear that posters are talking about different systems - this is why the first thing an applied mathematician or physicist does is to draw a diagram, and to state any assumptions. For example I think gbutler69 was talking about a system with the "hand" moving in a circle to impart a force to maintain the kinetic energy of the rock, where KE was being lost to air friction, and the responders were assuming a frictionless system with a rigid, fixed "hand".
To prevent a similar flamewar I should mention that in my example above, the rigid post is attached to the ground, which is also rigid and has infinite mass
Now, what are all the FORCES? What's that tug I feel on my hand that I have to exert energy to overcome? Oh, that's the CENTRIFUGAL FORCE my hand is experiencing.
Perhaps I'm going off the original point of the discussion a bit, but since this is all about understanding physics I thought I should point out that you do not need to exert energy to "overcome" a force. It's only if that force does work that energy is expended. Replace your hand with a rigid post and it will still experience a force, though it clearly doesn't expend energy.
Remember, UNIX spelled backwards is XINU. -- Mt.
