9/11/2014

Physics is Awesome and Physics is Weird

The first law of thermodynamics

by Mike Eats

When a candle is placed into a graduated cylinder, it becomes extinguished. When a candle is placed into a graduated cylinder and then another cylinder is placed inside, it creates a cycle. In this cycle the CO2 produced by the reaction from the flame and burning wax rises due to the heat and outside of the cylinder oxygen is pulled through by the raised temperature, causing a cycle which will keep the candle lit.

a Candle that is lit, inside of a large jar is then dropped, what will happen to the flame?
My group said it would burn more brightly.
We were wrong.
Because the static heat of the flame is lost when the candle is in free fall, The flame can no longer rely on convection for heat to speed up the chemical reaction. It must rely on diffusion which is not as fast a reaction for burning.

The spring is an example of a negative work reaction. Alone the spring does no work and just sits in equilibrium, only when work is applied to the spring to contract it is the spring able to do work.
Similar to a spring is a cylinder of gas at standard temperature and pressure. If work is applied to it, like a spring it can do work in return; likewise, if it is heated it can also produce work. 

This a review of the relationships between pressure, volume and temperature.
This shows the direct relationship between volume and temperature and between temperature and pressure.
This also shows the inverse relationship between pressure and volume.

These equations reflect the previous graphs. These two equations reflect the relationship between volume and temperature (#4) and also pressure and temperature (#5).  Using the ideal gas law and treating all the other portions of the equation as constant, this is an introduction to processes in which either the volume, temperature, or pressure is constant.

This final equation is using the relationship between pressure and volume when temperature is constant. This is a difficult situation as both pressure and volume must change without temperature changing, which though may be negligible is not necessarily constant.

This equation is calculating  work in a system without knowing temperature. In this case it is a water tower and it is lifting water using a change in pressure due to the heat. In this cause the equation for work is delta U. Because temperature is unknown the equation for work is P1V1 multiplied by the natural log of V2/V1. Much physics very wow.

This is the total work, it includes the work done by the the gas and work done by the fluid and finally work done by the mass of the water lifted.
The work done by the mass of the water is equal to mgh
the work done by the gas is PairVtln4
The work done by the air is 1/4PairVt
as the work  done by the mass is positive and the work done by the gas is in the same direction, it is the sum of those two subtracted by the work done by air.
air is the fourth derivative of displacement.

These are the graphs of pressure vs volume, and they identify the four processes that make up a heat engine. When temperature is constant and delta U is zero; it is an isothermal process. When pressure is constant the graph is a horizontal line and it is called isobaric. When volume is constant and W=0 the graph is a vertical line is called isobaric. The final equation is when Q is 0 and that is called adiabatic, the word is similar to Diablo, which is Spanish for the devil.

An example of a heat engine. It is important to recognize that in this engine it is only made up of isobaric and isochloric processes. Next the W and the Q and the delta U is all calculated for each step as well the energy for each step is looked at in each step. In this case energy is 3/2PV.

This board is the culmination of all the findings as well as the equation for efficiency.

This is the equation for efficiency, Conceptually it is the amount of work you get done by the amount of heat you put into the system. that being said the perfect engine would be rated at 1. This is the rating on the engine of the 2006 Chevy Colorado.

This is the practical application for a common efficiency of a heat engine.

This gas law apparatus is creating an environment with constant temperature. Because constant temperature is difficult to achieve, the experiment is not done tracking the pressure and volume over time, but at instantaneous moments.

This is using the previous device to calculate work. Because work is equal to the integral of P with reference to Volume, then pressure must be defined with regards to volume. This becomes the integral of nRT over V. nRT is all constant so it just becomes the natural log of the final volume divided by the initial volume.

#physics.
This is an example of a cycle and the idea of using heat to contract rubber and then allowing it to cool to expand.