Paint Parabolas

In my small math class (only 4 kids on this day), we rolled marbles in paint and then rolled them to make parabolas.  This idea is from Alex Overwijk @AlexOverwijk and his website: Slam Dunk Math

I didn't have too many details but I knew I wanted to use it as an activity to culminate our lesson on quadratics.  We would bring together what we knew about the properties of a quadratic graph and then do systems and regression with it using Desmos.

I tried the activity at home by rolling the marble in paint and making it roll on paper.  It didn't go very smoothly or in a parabolic shape.  I tweeted @AlexOverwijk for help.  He told me I should add a little water to the paint, perfect!

I had the kids pair up (all 4 of them) and practice rolling the marbles. 

Then, we went to the good paper - the big grid paper I bought so they could roll for real.  The first person rolled theirs and the other person had to roll it in the other direction so it would intersect twice - ah the pressure.  They didn't work out perfectly in one shot, but we went with it.  The kids could see the grids below but you may not be able to.

They did great and it went more quickly than I anticipated.  The whole lesson was one hour.

After they rolled for real, we cleaned up and took out the computers.  They need to find 10 good points on each of their lines and create a table of values.  Then, we turned to Desmos to do the regression.  They found the equations of each of their lines and then entered both into Desmos so they could find the point of intersection and "solve the system".  They had to continue and tell me each of the properties of their graphs as well - the vertex, the y-intercept, the x-intercepts, and the axis of symmetry. 

They did a great job and I thought it wrapped up the unit nicely.  Thanks Alex!