What variables affect how far a ball rolling down an incline will cause a box to slide?
Board or ramp, collection of various types of objects that roll, cardboard milk carton with the top cut off or other open box.
Release a ball from the top of the ramp so it rolls down the incline and into the milk carton. Observe the distance the carton moves along the floor.
List several variables you think may affect how far the carton moves along the floor.
Design and conduct experiments to determine whether or how your suggested variables affect the distance that the carton slides. Record your observations in an organized manner and tell what you have discovered.
In this activity the students measure if how far the milk carton slides is directly related to the energy that the rolling object transfers to the carton. The energy transferred to the carton is found by pulling the box by a spring scale to determine the force required to push the carton the measured distance. It is not necessary, nor even desirable, to have the students calculate the energy transferred to the carton. They should use the distance the carton slides as the dependent variable.
Allow them to explore the variables they think would affect the distance the carton would slide. One would hope they would explore, among others, the height of release and the mass of the rolling objects. Students can explore many interesting variables such as length of incline, release height, angle of the incline, size of ball, mass of ball, shape of rolling object, weight of carton, surface of carton, etc. Will a cylinder (like a pop can) filled with water have a different effect than a solid cylinder or one filled with sand? As a slight diversion, ask the students to predict which can would roll down the incline the fastest. The carton could be replaced
by a heavier box or block. The skate carts would work well to roll down the incline.
Don't attempt to have the students reach closure on all the variables. Hopefully they
recognized that the more energy the object had because of it's mass or weight and it's position the more energy it had to transfer to the carton. If students have questions whether a certain variable will affect the sliding distance, ask them to conduct an experiment or a test to find out the answer to their question.
Make careful observations of how students are conducting the experiment. Are they changing only one independent variable at a time? For example when they change the angle of the incline do they keep the height or length of ramp constant? Until students are formal in their cognitive operations, they may not control all the variables. Don't give them advance warnings, but rather, ask questions of what they will learn by a particular procedure or what they would do to test a certain hypothesis.
After discussing the summing up questions, challenge the students to condense their list of variables so they understand that other than friction, only the mass of the ball and the height of release affect the distance that the carton slides.