Variables
What is a variable? A variable is a thing that always changes e.g If you are rolling a marble with your left hand then you roll it with your right you have changed a variable.
What were the variables we changed? We changed everything about our ramp. We also changed a variable on where we were testing.
How many variables should you change at once and why? You should only change one at a time unless you are making a different ramp/object because you might change a lot of things at once and it might make a little difference but you might not know what change made the biggest impact.