MIT Massachusetts Institute of Technology

Recognizing Forces: Does the Floor Know when You Put on Weight?

Aaron Osowiecki
Physics Teacher
Boston Latin School
Boston, MA
Lead Developer, Energizing Physics

Jesse Southwick
Physics Teacher
Boston Latin School
Boston, MA
Co-Developer, Energizing Physics

This beginning Physics lesson introduces students to forces and free body diagrams (i.e. force diagrams).  Rather than modeling forces in abstract situations, this lesson challenges students to develop diagrams that accurately describe the forces acting on them as they participate in the lesson activities.  After introducing the force of gravity and normal force, students build their own free body diagrams using the data provided by a bathroom scale.  Students will build three free body diagrams providing formative assessment opportunities for you and your students.

The lesson confronts the following student misconceptions:

  1. The scale measures the force of gravity.  The scale actually reads the normal force pushed up onto you by the scale.
  2. The normal force always equals the force of gravity.  In fact, they are not always equal, as students will see.

Through this lesson, students will investigate real forces while learning how to develop visuals to represent those forces. The lesson can be completed in one 45-60 minute period, with no materials required other than a bathroom scale. There are few prerequisite beyond a basic familiarity with mass and using units. 

 After attaining a BS in Mechanical Engineering and spending four years as a Naval Officer, Aaron joined the staff at Boston Latin School in 1999. Intent on shifting the classroom towards the students, Mr. Osowiecki led the development of “Energizing Physics’, a progressive physics curriculum used at BLS and other schools throughout the country. He attained National Board Certification in 2011 and was selected as the 2016 Shell Science Teaching Award recipient for 2016. Mr. Osowiecki teaches Physics 1, AP Physics Electricity and Magnetism, and sometimes Environmental Science. He has presented at national and regional conferences for many years. He enjoys playing sports, guitar, reading, hiking, biking, and hanging out with his family. Read about “Energizing Physics” at:

Growing up in the Jamaica Plain neighborhood of Boston and attending the Boston Public Schools, Jesse attended Boston Latin School and then majored in Physics at Princeton University. He returned to his Alma Mater, Boston Latin, in the fall of 1998, where he has taught ever since, with the exception of one year on a Fulbright Teacher Exchange to Istanbul, Turkey. He has most frequently taught Physics 1 and AP Physics C, and contributed as second author to “Energizing Physics.” In addition to teaching, Mr. Southwick has completed an MAT in Physics Education at Northeastern, participated in new teacher preparation programs with Boston University and the Boston Science Partnership, and presented at conferences with Aaron. He lives in Jamaica Plain and enjoys running, reading and traveling with his family. Read about “Energizing Physics” at:

This is the website for the course, Energizing Physics, created by Aaron and Jesse that organizes their teaching of physics around the concept of energy.

This site is a simulation for exploring the Normal Force created by Boston University Physics Professor, Andrew Duffy.

This site, sponsored by the Physics Classroom, provides instructions on drawing Free Body Diagrams, as well as practice situations for applying the instructions.

This site, hosted by Varsity Tutors, provides study concepts, example questions and explanations for AP Physics 1, relating to the Normal Force. 

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