Agroup of students is investigating whether the force of friction depends on the nature of the surfaces in contact. the students push two pieces of wood each with the same force on a table. one piece of wood is smooth and the other is rough. the distance traveled by each piece of wood is shown. experimental observations student 1 student 2 student 3 student 4 distance traveled by smooth piece of wood 20 cm 18 cm 16 cm 19 cm distance traveled by rough piece of wood 15 cm 12 cm 10 cm 11 cm what was the outcome variable (dependent variable) in this experiment? distance traveled smooth wood rough wood number of students