What I learned in inquiry 6 is that Friction pushes things back when it goes forward, more mass equals more weight, and that surface area also is a variable of how much friction their is
The way we measured sliding friction is we used a spring- scale to measure the push that friction causes on the block. The push friction causes can be measured 'cause it's trying to stop the block, which causes force which can be measured.
I learned that control variables are variables that you don't change, some examples are: Pull Distance, Pull Speed, and some others you should be able to think of. (But there are MANY more!)