Newton's Second Law: Constant Force Applied to a Skateboarder

This activity is designed for students to create an experimental procedure and collect data.
This activity is designed for students to analyze their data and draw conclusions about relationships between force, mass, motion, and friction.
Students will discover that bodies acted on by a constant force tend to accelerate.
Students will qualitatively discover and describe Newton's 2nd Law of motion.

This lab activity can be done with any class grades 9-12 that is studying Physics. It can be done with basic, general, or advanced students if properly modified. It is best done in groups, so any class size will work. The activity should be done during a motion unit while introducing Newton's Laws of motion. It will require approximately 2 regular class periods or 1 block period. Special equipment needed includes skateboards, stopwatches, a graphing program on the computer (optional), and a smooth stretch of floor at least 7-10 meters long.

Students should begin by making and justifying predictions about what type of motion will result from the application of constant force to an object. Next, describe the goal of the experiment to students—they are to produce distance vs. time graphs for various people on skateboards being pulled with a constant force. Within each group, 3 people of different known mass should be used, and at least 2 force values should be used for each person. Describe the uses and locations of the equipment (skateboards, masking tape, stopwatches, scale that measure in kg). Have students get into groups and develop their own methods for conducting the experiment and measuring data. When they are done, have them graph the data and draw conclusions about the type of motion produced (constant speed, acceleration, etc.). Students should also analyze the effects of friction and sources of error. Finish the activity by officially introducing Newton's second law and have students describe how their results show the predicted relationships between mass and force and acceleration.

- There is some risk of injury in this lab, so be sure to stress safety and have each group provide a "spotter" to keep the skateboarder from falling.

- Volunteer to ride the skateboard in one of the trials.

- Some students will want to do tricks and show off on the skateboard, slowing things down and possibly causing damage to the room. You may want to have these students show off in a controlled way for the whole class at the beginning or end of the activity just to get it out of the way.

- This activity can also be done (more precisely) with Vernier motion detectors, if you have enough of them.

- This activity could also be done as a demo to save time.

- Put away all fragile items before doing this activity.

- I have done this with 9th graders, conceptual 11/12th graders, and advanced 11/12th graders. They all enjoyed it.

Students can be given a lab/participation grade based on their involvement in the activity itself.

Students can also be graded based on their completed lab sheet, graphs, and analysis.

Based on Minnesota Academic Standards Grades 9-12 for Science (Draft, January 2004)

I.B.1 Design experiment and analyze data
I.B.3 Apply model to data and support conclusions
I.B.4 Identify sources of error

I.D.1. Use Newton's Laws of motion
I.D.2. Describe effects of friction

I.E.2. Identify dominant forces in a system