Whenever I teach a new group of students I always like to start with a nocussing unitsmeasurement lab to get them thinking about how they measure something and what it means when right down a measurement.  We talked about units a bit and how metric units are easier to work with then units like feet and inches (width of your thumb) and I put my poster about forbidden 4-letter words (inch, mile, etc) back up on the wall.  I didn’t make this poster but I love it.

I asked the students (8-12 years old) to estimate the length of my kitchen table (if I was in a classroom I use the length of the chalkboard).  The chalkboard or something longer like a fence or the side of the house works a bit better because they really have to think about how many meter sticks would fit across it, while the table was pretty clearly near 1.5 meters which is what they all estimated.

hand spanThen we measured the length of the table in hand spans – length from pinky to thumb with your hand stretched out. If you’ve read my other physics posts this might all seem familiar, like I said, I do this in the beginning of most of my science classes. The kids counted how many hands it took to go down the length of the table and answers varied between 8 and 13.  We discussed why the answers were so different – different sizes of hands, some kids actually used their hand in a different orientation, miscounting, etc.  We also talked about why its important to put units on a measurement,  saying the table is 10 long doesn’t tell us anything, 10 ft? 10 inches? 10 cm?  Units are important! I also asked them how sure they were of their measurement.  Would they bet $50 that if we brought in another kid and they measured the table they would say it was 10 hands long?  They all said no, and that they didn’t have that kind of money to begin with.  But then we measured the table with meter sticks to the nearest mm and they were willing to bet $50 that someone else would measure the table and find its length to be between 1.62 and 1.63 meters long.  I told them when scientist report measurements they also put an uncertainty on their measurements so we can tell how precisely they measured it.

Then we moved on to Weighing In Around the Solar System from the Real Science Odyssey Physics curriculum.  We talked about the difference between mass and weight and they seemed to have a pretty good grasp on weight and knew it was caused by the force of gravity, one kid even knew that his weight on the moon was going to be 1/6 of his weight on Earth.  We then watched the following Veritasium video on mass vs weight.

We also talked about the vomit comet (plane which flys in a parabolic orbit to simulate free fall – zero g)  for awhile when one kid mentioned zero gravity, so I had to show this amazing music video by OK Go which was filmed entirely in a vomit comet with no special effects except PHYSICS.

I didn’t show this in class, but its a nice explanation of the vomit comet and weighlessness.

For the lab the kids just had to measure their weight using a scale and then calculate their weight on different planets.   We talked about how the bathroom scale was measuring the force of gravity pulling you towards earth and that it would give a different answer if we were to use the same scale on the moon or another planet.  I also showed them a balance and how it measures mass by comparing the unknown mass to known masses and how it would give the same answer anywhere.

When they were done filling out the table they were a bit wowed by the fact that they would weight around 2000 lbs if they could stand on the surface of the sun and that their weight would not be all that different on Saturn, which is huge, but its not very massive.  The Exploratorium has a nice website , Your Weight on Other Worlds, where you can type in your weight on earth and it shows you your weight on the other planets, moons and even stars!

We had a few extra minutes at the end of class so we watched the Brainpop on Measuring Matter. If you have kids younger than 13, you really should invest in a subscription to Brainpop, my kids loved it when they were younger.  The videos are great and they have them on all kinds of subjects. My youngest used to watch a few brainpop videos every night before bed, for years!  You can watch them on ipads, or if you use a desktop you can watch the videos, play games and find activities/labs to do as well.  Well worth the $100 a year.