Work with syringe and fire syringe

Work with a Syringe     

For the first experiment, connected a practically frictionless syringe to a tube that was connected to a flask.  The flask was put into a hot water bath and as we watched, the syringe moved up.  This was because the syringe is at a constant pressure, so in able for the pressure to stat constant, the volume had to increase.  Also, when gas molecules increase in temperature, they move and bounce around more and in turn push the plunger upwards.

As the syringe was moving up, Professor Mason placed his finger on the syringe and applied some type of force to the system meaning the system is applying a force on his finger and doing some work. When this happens, the gas molecules are forced into a smaller volume and the energy that the added because of the force is stored in pressure and temperature.  When the syringe is let go, it moves upwards more because of the stored energy.


He then placed the flask into a colder beaker of water and the syringe began to fall because not only are the molecules moving slower now because of the decrease of temp resulting in a decrease in energy, but for the system to stay at a constant pressure, the syringe must decrease in volume as the temperature decreases.







We derived an equation for work that showed the relationship between pressure, force, volume and work as can be seen in the image to the left.  We stated that work is the integral of force times some distance moved dx. It is also known that force is equal to the pressure times some area.  So if you replace F=PA into the work formula you can see that work is also related to pressure times some volume changed dV.  We also began to explain the first law of thermodynamics as how the change in internal energy is equal to the amount of heat put in (like placing the flask into the hot water) minus the amount of work done (professor mason pushing down on the flask) which would create a change in internal energy.  If we were to explain this concept to a child, i would start by telling them to rub their hands together when they are cold.  The result in the change of temperature they made to their hands was the amount of heat they put in minus the amount of work they did to get that heat there!

The Fire Syringe

For the fire syringe we took a plunger, some cotton, and some muscle to set a piece of cotton on fire.  We began with measurements.  We measured the initial length of the tube, the final length on the tube, and the radius of the tube.  We the used the calculation V1T1^(5/2)=V2T2^(5/2) and solved for the final temperature that the cotton would burn at.  We knew right off the bat that the cotton should at least burn at 451 degrees Fahrenheit because that is the temperature that paper burns at.  Our initial trial didn't set the cotton on fire because it didn't create enough energy to heat the surroundings to 451 Fahrenheit.  Although, our second trial did catch a successful fire.

After solving for T final we determined it to be 849.9 K or 1070.3 degrees Celsius.  We then propagated uncertainty (below) because we had a lot of systematic error in our values especially with guessing the temperature of the room to be 20 degrees Celsius. We found our uncertainty to be +/- 29.66 K and even with our uncertainty subtracted from our final answer, our fire still did not burn at 451 Celsius, but this makes sense.  Because there is now less volume in the syringe (because we pushed down on the plunger very fast) the collisions between the particles because much more frequent and faster causing the temperature to rapidly increase with the movement of the particles rapidly increasing.  So as the syringe goes down, the area of syringe and the space for the particles to move around decreases so there is many more collisions in a short amount of time.