Air Pressure

Air Pressure

Air Vent valve for Solar Water Heater Pressure Relief valve size1 2 copper
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How to find the air pressure in the gap of a pop can?

In a pop can, there is usually a small gap between the actual soda and the can. With only the basic science equipments (ex: graduated cylinder, beaker, weighing scale), how could the air pressure in the gap be found?

The first respondent is wrong about shaking the can making the pressure go up. That doesn't happen unless you believe thermodynamics is wrong. Shaking a can of soda doesn't increase the pressure, the soda will explode after that when opened not because the pressure is higher, but because you have entrained bubbles into the soda, which rapidly expand when you open the can. Anyway ...

The following method assumes that your weighing scale is precise enough to measure very small changes in mass. It also assumes that the can volume doesn't change when you depressurize it. I'm not sure this last assumption is valid to the limits you need, but I don't see a way to do it otherwise.

1. Weigh he can *before* you open it. Record the weight.

2. Open the can but do not drain any soda out of the can. Let it stop bubbling and the weigh the can again. It should weigh just a little less than before. That difference represents the mass of CO2 (carbonation) lost to the atmosphere when the can was opened.

3. Pour out the soda into the graduated cylinder and measure the volume of the soda. You have to make sure you get every last drop of soda.

4. Use the graduated cylinder to measure the total volume of the can by adding water back into it until it is totally full.

5. Calculate the headspace volume (gap size) by subtracting the volume from 3 from the total volume from 4.

6. You now know the total mass of gas lost and the volume of the headspace. From the mass lost you can calculate the number of moles. Then use the ideal gas law:

P*V = n*R*T

to calculate P (pressure) as nRT/V where n is the number of moles of CO2, R is the gas constant (0.082057 L-atm/K-mole), and T is temperature in Kelvin. Add this P to the 1 atm of pressure and you will get the total pressure of CO2 in the soda can gap. You should come out with a number in the range of 2-3 atm.

edit: Shaking a can of soda does not increase its internal pressure. If you believe that then tyou do not understand thermodynamics. The internal pressure of a can of soda is determined by Henry's Law and the concentration of CO2 in solution. Shaking the can does nothing, nothing, to change anything related to those two things. Similarly, mechanical agitation, so long as it does not disrupt the integrity of the can, cannot cause the can to rupture. When a can is dropped it may burst, but that is from a shock wave propagating through the can and is a transient phenomenon. There is no increase in equilibrium pressure in the can. What shaking does is entrain many small bubbles into the can of soda. But no more CO2 comes out of solution. See reference below if you won't listen to common sense from me and stop pontificating wrongly about stuff.

Keep yourself informed about air pressure in the tires with Tire Pressure Monitoring System

Cars in Unites states were not equipped with Tire Pressure Monitoring System till September 2008, however after that all the cars and light trucks were sold for the purpose of installing Tire Pressure Monitoring System in them.

Tire Monitoring Pressure System is also referred to TPMS. This system alerts the driver about the air pressure level in the tires, thereby preventing any severe damage. Therefore, make every possible effort to ensure that TPMS works effectively with the tires of your vehicle.

Basically, Tire Pressure Monitoring System is classified into two categories: Direct TPMS and Indirect TPMS. Both the systems differ from each other on the basis of their functionality. TPMS consist of a sensor which is located on either sides of the vehicle and a receiver attached to the vehicle's computer. The sensor in the vehicle transmits the signal to the computer in case of low tire pressure.

You do not need to worry while changing the vehicle. While installing new wheel, simply transfer the sensor from the factory setting. In some vehicles, sensors are allied to valve stem whereas in some cases sensors are attached directly to the center of the wheel. So, take all the precautionary measures to mount and dismount the tire. Apart from that, installing new sensors in the wheels is not a big deal.

While installing new sensor in the tires, ensure that sensors does not interfere with the design of the wheel. In case, sensors are interfering with the design, you can purchase a valve stem to hold the sensor.

Tire Pressure Monitoring System requires proper servicing to work effectively. Get a good service manual and take a note of all the details such as resetting and reprogramming the sensors, etc to get the most. Moreover, there is Tire Pressure Monitoring System tool which helps to test the sensors for the proper functioning. So, contact a good supplier and select the sensor that suits your needs.

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Air Pressure - Science Theater 4