For his science fair experiment, cole decided to determine how different types, of surface material , affect how fast a matchbox car will go. he chose to use a tile floor, concrete patio and carpet. he used the same car for each of the 20 trails. he measured the distances the car went after riding down a 1 meter-ramp. what is cole's test ( independent) variable? what is cole's outcome ( dependent) variable) ? what must be kept constant ( the same) for every trail? what do you predict will happen and explain why.