For the high school physics class I asked the students to watch the following video on speed and velocity before class.

I also sent them the link to this video by Smarter Every Day on ice skating, since the textbook we’re using, How Things Work: The Physics of Everyday Life, uses ice skating to start talking about motion and forces.

I started class with an inertia demo and I had 5 of them so they could all try it while waiting for everyone to arrive. All you need is a bit of cardstock (or file folder) cut and taped into a loop, a narrow mouthed jar, or water bottle and a lego block, nut or other small object. I got this idea after browsing Steve Spangler’s website where you can actually buy the inertia challenge as a kit. By putting a finger or two inside the loop and moving them quickly to the side you knock the paper loop away and the lego will fall into the bottle. The lego falls straight down because you are only exerting a force on the loop of paper and once its gone there is nothing to hold up the lego and it falls into the bottle. This is similar to pulling the table cloth out from under dishes, but not quite as messy if you do it wrong.

After a discussion on speed, velocity, scalars and vectors, I showed the students how to use the Video Physics app to record the motion of objects. Since we were interested in constant velocity I set up the air track and glider and had an air-powered soccer disk (basically a small hovercraft which glides across the floor) which they could use.

The meterstick in the movie is used so you can set a scale in the Video Physics app. You can also set the origin for your coordinate system. The app can then graph distance as a function of time with the correct units (if you did it right). Data can also be exported to Graphical Analysis app where you can tweak the graphs and make them look nicer for printing. I had the students make one graph by hand so they could learn how to do it.

If the object is moving with a constant velocity the data points will fall on a line. Students used a ruler to draw the best line through the data points and can calculate the velocity of the object by finding the slope of the line.

Below is a frame grab from a movie of the glider moving with constant speed on the air track. The red dots indicate the position of the glider at equal time intervals (each frame of the movie) and since they are roughly equal distant from each other we can conclude the glider is moving at constant speed. For a more detailed description of this set up please see my post from the first time I taught this lab, Homeschool physics 003. Next week we’l doing 1.2 in the text, falling bodies.