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Wednesday, November 5, 2014

Math is Real Life: Watts Up?

Today I am linking up with 

A monthly REAL WORLD math blog link-up hosted by

In the last several months, my local electric company has seriously upgraded their technology.  They have installed smart meters and made huge updates to their website.  I can now pay my bill online and generate graphs and statistics for my power usage by the month, week, day and even hour.  As I was playing with all of these graphs and statistics, I started to think about how important it is for folks to understand how their choices will effect their bill.  Bringing this into the classroom would be a great lesson for all!

I think this lesson is best done in upper elementary through high school.  It is an important real life skill and could be incorporated into a lesson on decimals, proportions, graphing or measurement conversion.  I spent some time analyzing my electric bill with a group of sixth graders.  

This lesson took about 20 minutes but gave kids a real look into how electricity consumption is measured and billed. 

Here is how the lesson unfolded

1) I had kids pair share and then share as a whole group their ideas around how electricity bills work and how you know what you have to pay each month.  There were a few kids with surprising amounts of knowledge about this but many kids had no idea.

2) I signed into my online account for my house.  We played with the graph generator looking at electricity usage over the last month

When we originally did the lesson with started with a graph of electricity usage over the past month.  Here is an example I generated recently.  

Looking at my usage for a month led kids to questions what was happening on the days were usage was very high and what was happening on days where usage was lower.  This led to looking back through a calendar to figure out what days of the week each date fell on.  They were quickly able to see that more power was being used in my house on weekends.  This led to some great discussions about why this was happening.  As these discussions took place, they wanted more details about certain days.  Using the graphing tool, I was able to get an hourly look at power usage for any day I chose.

A look at the hourly usage on an average day

A look at the hourly usage on a very high day.   Because I was graphing a recent day both during my original lesson and again for you today, I can tell you exactly why the power usage jumps so high on this day.  I was doing laundry and used my dryer for 2 loads.  It is very obvious from the graph how much electricity my dryer uses!
 Looking at these graphs led to a great discussion about why power usage is so high or so low.  Many kids thought it was just because more people were in the house but others argued that what we were doing was more important.  This led to discussions about why power was being used every hour even when we were not home.  I asked them to think about that for a minute and then showed them a graph of our power usage when we were on vacation.  Some kids were shocked that power was being used even when we were out of the house for an entire week.  

As we were having these discussions and talking about what in our homes uses power, I clicked on a link to our state's energy efficiency collaborative.  On their homepage, we saw a picture of a power meter and learned that one of their services was to lend these things out for a month at a time.  The students thought this sounded like a great idea.  They wanted to know what was using all the power in my home and report back to them.

My efficiency collaborative sent me a Watt Meter and I got to work following the directions.  Anything that cycles on and off like a fridge or freezer has to be plugged in for at least 24 hours to get a good view of power usage over time.  The meter has settings and modes galore and you can easily see how many watt-hours you are using and the estimated monthly cost of that appliance.  You can also use it to plug in things that don't cycle on and off like toasters, tvs and such that are either on or off and get a reading on how much power they are using if they are on and what they are using when they are off. 

I wrote down all the numbers I got in kilowatts.  I brought my results into school and had kids help me figure out how manykilowatt hours I was using and how much each appliance was costing.  This fancy meter actually does all kinds of conversions and cost analysis for you but that takes all the fun and math out of it!  The students brainstromed a huge list of ideas that I could try to save power.  Then we plugged the watt meter into various things around the classroom and did out own analysis of how we could save power at school.  A huge aha moment for kids was how much power is used by things that are not on.

Since doing this lesson with students and having these discussions, I have made some changes to the way I use power in my house and we have made some changes at school.  My favorite change is the new power strips I am using for things like my TV and computer.  It is called a smart strip and really reduces the amount of power being used by things that are off.

  There is a lot of math in power usage and paying for power and analyzing usage is a great real life math skill.

Any ideas about how I could continue this "powerful" education with my students?  Let me know in the comments below!
I am also linking up with Middle School Math Moments for Workin' on it Wednesday!


  1. I did a similar project with my physics students. I think it was really useful. How exciting that power companies are beginning to provide this information!

  2. I love the idea of taking the graphs in for your students and having them make connections to how their choices can affect money being spent! Thanks so much for linking up!

    Jamie aka MissMathDork

  3. I, as well, love to do real world math w/my students. A lesson called harvest.pdf uses math from the Department of Agriculture. I found this math activity for fall harvest at on the TEACH link.

  4. This was an awesome idea for connecting math to the real world. I bet your students will never think about using electricity in the same way again. Bringing in the graphs of your electricity usage was a great conversation tool, and I found in interesting how much more aware of what might be causing the increase in electricity use after just one time of exposure and discussion! You might could see if some of the other teachers would allow you to bring in graphs of their usage and your class could have a comparative analysis topic of discussion

    1. Great ideas! Since we all have the same utility company I know they can all access their graphs online. I bet I will find a bunch of teachers willing to share. Thanks for the suggestion!