Saturday, April 28, 2018

Some Science While Mowing the Lawn

I have about 20,000 square feet if lawn to mow and I need to mow it about twice a month during the warm part of the year. So while mowing today, I thought I would do a little science. I used several cellphone apps to get my data and I can see several more opportunities with additional apps.

First, I used my sound meter app to find out the background noise in the front yard is around 43 dB. With the lawn mower running, the noise is 80 dB at my ears' location. An increase of 37 dB appears to be over 5,000 louder in terms of power. I need to double check my results and make sure u am not confusing my units. It appears audio us measured in terms of power amplification, so the online calculator I used may have been the wrong one for my situation.

Next, I used my FFT app to look at the sound of a lawn mower. Below are the results.
Without the lawn mower running, this is the noise present in my front yard. It's scaled way out because the lawn mower is so loud. There's more data visible, when I zoomed into the screen. The one peak is due to The cell phone vibrating when it recorded a screen capture.

With the lawn mower running, this is the FFT app display. The scale is the same as the previous image. 

 Finally, I weighed the bags of grass clippings and counted the number of bags needed to mow the lawn.

Each bag of grass clippings holds 11 pounds of clippings. It took 15 bags of clippings to mow the lawn. That's a total of 165 pounds of grass clippings that I will use to mulch my garden rather than dump into a landfill. Since I need to mow twice a month for seven months, I should be preventing 2,300 pounds from going to the landfill.

Grass, like all plants uses photosynthesis to convert carbon dioxide and water into carbohydrates. The carbohydrates become food and cellulose (among other things). The chemical equation looks as follows,

6CO2 + 6H2O -> C6H12O6 + 6O2.

Converting pounds to grams and grams into moles, I find that 165 pounds of grass required 242 pounds of carbon dioxide and 99 pounds of water. It also generated 176 pounds of oxygen.

Now there are several problems with this calculation, the major being that the grass wasn't dried out. So my 165 pounds actually consists of cellulose and water (and trace other materials). But it's good enough for a first stab at the problem.

What's next? Maybe letting the grass dry out before weighing it. Then calculating the amount solar energy used by the grass to generate thus amount of cellulose. Then, I need to find the solar insolation for the Treasure Valley. With that, I should be able to get an idea of the efficiency of my lawn.

Hey, rather than look up the isolation, I could try measuring it by how fast materials warm up in the sun.

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