Work

Spring 2015, Prof. Mason

5 March 2015

We started the day with an experiment. By connecting a syringe to a isolated flask, we want to find the pressure on the syringe when temperature increases. When the flask is placed in the heated water in the beaker, the syringe end is pushed up by the expanded gas and increasing the volume in the syringe. This shows the work done in the syringe.

Next, we want to know the relationship between work and pressure. Work that we have known from our past physics class was W= Int of F.dx and Pressure was F/A. By combining these two equations together, we found the Work to be int. of PA*dx.

Thus, we know that the graph of Force vs. distance will give us Work as well as the graph of Pressure vs. Volume by calculating the Area of the graph.

We have known from our past physic classes about Newton's first law; Energy can't be destroyed nor created, it can only transform to a different type of Energy. We chose to explain this law by using the example of skidding tire. When tire is skidding, we can hear and see the energy in a form of sound and smoke. That's because energy from the skidding tire transform.

From this law, we found the equation to be E=Q-W. From this equation, we derive them to find work, heat, pressure, kinetic energy, and relationships between them. The velocity in x direction is x/delta t of x and in y direction is y/delta t of y. To find velocity total we use 3D-Pythagorean theorem. Given than Vx square, Vy square, and Vz square equal to each other, we know by the Pythagorean theorem, total v square equals to 3 Vx square. We know that when the molecule bounces back on the x direction, it will be 2 delta t of x.

We found the pressure to be NmVx(square)/x(square), but we know that Vx (square) is Vt(square)/3 and x(square) is volume. By replacing this we get MVt(square) in the numerator, which is the same as 2KE; thus, we can replace this and found the relationship between pressure and kinetic energy.

Next we want to find the relationship between Temperature and root mean square velocity. We know that PV=NKbT. From there, we found T= 2/3 K/Kb. By replacing the K into its rquation that we know, we found the Root mean square velocity.










Given that the system is isothermal (temperature is constant), we then know that change in internal energy is also zero.

Given that the system is adiabatic (Heat is constant), we then set change in heat to be zero, and find the internal energy to be equal to negative work. From earlier, we have found change in internal energy to be 3/2 NKbT, and Work is int. Of PdV. Replacing the variables with this, we found the relationship between temperature and volume, which Temperature is -2/3 of Volume in ratio.

Last experiment, we are using the fire. We want to change volume without changing the pressure. By pressing the platform very quickly, we are going to avoid change in pressure as seen in the video below. The temperature increase very rapidly when doing this. First, we collect the data before doing the experiment. Then, we make some calculations to predict the final temperature. The ignition point of cotton is about 210*C or 483K. We found the final temperature to be 2860.8K. Thus, the cotton did light up as shown in the video as well.