Gas station without pumps

2012 September 4

Disappointing gas law demos

Filed under: home school — gasstationwithoutpumps @ 15:04
Tags: , ,

We tried playing with some of the gas-law physics toys I’d bought from Arbor Scientific, with somewhat disappointing results.

Demo 1

Pressure pumper image copied from Arbor Scientific web site.

Strip thermometer image copied from Arbor Scientific web site.

The first toy was an “individual pressure pumper“, a little $3.25 pump for adding pressure to soda bottles, together with a $1.25 strip thermometer for measuring the temperature in the bottle.

The idea is that you pump up the bottle and note the rise in temperature as you add energy, then release the pressure and note the drop in temperature.  We sort of got this effect, though a lot of pumping was needed to get even a small change in temperature. Small amounts of sunlight caused much larger changes in temperature.

We switched to mounting the bottle on a rocket launcher and pumping it up with a bicycle pump.  Pumping up to 60psi raised the temperature from 70°F to 90°F, which was a gratifying demo, but releasing the pressure by holding the bottle and triggering the launcher blew the thermometer out of the bottle and damaged it in the process.  The temperature in the bottle had clearly dropped (as evidenced by condensing water vapor), but the thermometer could not react to that fast a temperature change.

So the demo with the individual pumper sort-of worked and with the bicycle pump worked once, but damaged the strip thermometer.

Demo 2

Fire syringe copied from Arbor Scientific web site.

The second demo of increasing temperature on compression was a fire syringe, a $19 toy. The idea is to put a little cotton lint or paper in the bottom of the cylinder, then press down rapidly on the piston to get a flash of light as the cellulose ignites.  This should have been a really flashy demo.

On the first try, the piston was not perfectly vertical, and the plastic top that holds the piston in alignment split.

On the second or third try, we got ignition.

We were unable to repeat that despite several more tries, as the o-rings sealing the piston to the cylinder were no longer holding air, and the piston traveled freely without compressing the air.  The fire syringe does come with two spare O-rings, but we did not try replacing them.

Basically, this looks like a one-use toy, which is rather disappointing for the price.  Even if the top had not split, the O-rings don’t seem to last long, and in a classroom would need replacing every year (if not more often).

Demo 3

Image copied from Arbor Scientific website.

The one physics toy for gas laws that did work properly was the Elasticity of gases demo, a $13.50 toy.
We did not use this today, as we had used it effectively last spring.  Of the three gas demos we bought from Arbor Scientific, this is the only one that seems to be worth the money, and it is pretty much a one-lab device.

We’ll try to do the homework for Chapter 13 this week (I’ve not even finished reading the chapter yet, though I’ve done the first homework problem) and get into the E&M chapters after next Tuesday.

1 Comment »

  1. Fire pistons are fun, but tricky to use. I ordered mine from Amazon which has several to choose from. And there are links to instructional videos on youtube. I lined the inner piston with vaseline with each attempt. They are popular among survivalists, but I prefer matches.

    Comment by Vida — 2012 September 7 @ 11:33 | Reply


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