Engineering Dynamics

Free Body Diagrams and Fictitious Forces

« Previous | Next »

Session Overview

Covered this week: In week 4, we practice using free body diagrams to help us find equations of motion. We do several example problems. We discuss the concept of a fictitious force as well as the hazards in using them. Computer-generated free body diagrams for a moving elevator. Image courtesy of Waifer X on Flickr.

Assignments

Problems and Concept Questions

Each problem set has concept questions paired with most problems. Answers to the concept questions are handed in before the overall problem set is due. You should therefore answer the concept questions in each problem set while watching the video lectures for the week. Then, use the Concept Question Answer Key (below in the Check Yourself section) to check your work before continuing to work on the problem set.

Please note that if your answer to the concept question is incorrect, it is likely that you may start down an unproductive pathway to a solution. Try to fully understand the answer to the concept question before you begin the regular problem.

• Problem Set 4: Problems and Concept Questions (PDF)

Videos

Lecture Videos

• Watch Lecture 7: Degrees of Freedom, Free Body Diagrams, and Fictitious Forces

  • Video Chapters
    • Muddy card discussion
    • Degrees of freedom and free body diagrams
    • Example 2: Hockey puck
    • Example 3: Rod leaning on a wall
    • Free body diagrams with two bodies
    • Fictitious force in the elevator
    • Fictitious centrifugal force

• Watch Lecture 8: Fictitious Forces and Rotating Mass

  • Video Chapters
    • Reading assignment from Williams on kinematics
    • Concept questions intro showing problems
    • Concept question discussion-spool and string etc
    • Fictitious force: elevator cable breaks
    • Demo of cart on incline with water in container
    • Complete fictitious force discussion
    • Rotating mass demo related to homework 1

Recitation Video and Notes

• Watch Recitation 4: Free Body Diagrams
  • This recitation reviews free body diagrams and covers a problem with a torsional spring pendulum followed by a second problem with a rolling pipe on an accelerating truck.
• Recitation 4 Notes: Torque and Angular Momentum, Pendulum with Torsional Spring, Rolling Pipe on Moving Truck (PDF)
  • These recitation notes were compiled by Prof. David Gossard, another instructor for the course. His notes go over concepts and problems covered during the recitation sections he taught, and may not precisely correspond to the content covered in the above recitation video.

Check Yourself

Concept Question Answer Key and Problem Set Solutions

The solutions are presented in two files, one with the answers to the concept questions, and one with solutions and in-depth explanations for the problems. Work the problems on your own and check your answers when you’re done.

• Problem Set 4: Concept Question Answer Key (PDF - 1.7MB)
• Problem Set 4: Problem Solutions and Explanations (PDF)

Looking for something specific in this course? The Resource Index compiles links to most course resources in a single page.

« Previous | Next »