Wednesday, 11 March 2009
All about Heat ♥
9:06 pm
In class today, we discussed about dynamic equilibrium. According to wikipedia, "a system in dynamic equilibrium is a particular example of a system in a steady state. In a steady state the rate of inputs is equal to the rate of outputs so that the composition of the system is unchanging in time. For example, a lake is in a steady state when water flows in at the same rate as water flows out. The term dynamic equilibrium is used in thermodynamics for systems involving reversible reactions. It is said that the rate of the forward reaction is equal to the rate of the backward reaction. Both reactions do in fact occur, but to such a minuscule extent that changes in composition cannot be observed." (http://en.wikipedia.org/wiki/Dynamic_equilibrium)
So, we can see that dynamic equilibrium is where a system includes some reactions that can be reversed.
Now,this brings us to the topic of static equilibrium.
We have seen that objects do not move when the sum of the forces acting on them is zero. We can use this fact to find the conditions for "static equilibrium": the condition an object is in when there are forces acting on it, but it is not moving. The conditions for static equilibrium are easy to state: the sum of the (vector) forces must equal zero, and the sum of the torques must equal zero:
S F = 0
and
S t = 0.
(http://www.rwc.uc.edu/koehler/biophys/2h.html)
Hence, static equilibrium occurs when the clockwise moment=the anti-clockwise moment.
Another interesting question came up during our class. Why do penguins stay at the south pole while polar bears stay at the north pole? Well, my answer during class was that maybe penguins originated at the south pole while polar bears originated at the north. Since neither can survive in a tropical climate, both are stuck at their respective poles. You see, to cross from the south pole to the north pole and vice versa, one would definately need to cross the equator, where there is a tropical climate. So, the penguins have to stay at the south pole as they would die if they tried to cross the tropical countries. The same goes for the polar bears.