i need an example or suggestion for a controlled experiment for a science presentation if you guys can . also don't have it be anything about plants.
! : d

Experiment with what rolls faster by covering one of two planks with a smooth lining like shelf paper and then do the other with a rough lining like carpet or astroturf. Place the planks at an angle and roll a tennis or golf ball down each plank simultaneously. Observe which ball reaches the ground first. In most cases, the ball will move fastest on the smooth surface, demonstrating the effect of friction on an object's acceleration. In this experiment, the controlled variable is the angle of the board and the type of ball you roll.

Put nails in different waters and see which one rusted the most. Btw drop all of the nails in at the same time

Digestion because it removes waste