BoxSand's Resources

Introduction

This is a picture of two scenarios with the same person in the same elevator. In the first scenario, the man, a scale that the man is standing on, the elevator and the rope are all part of the system and there are arrows depicting the various forces present and its direction. In the second scenario but with the system of interest only drawn as a circle around the man which does not include the elevator or the scale. This is to show that the problem can be made simpler if we only take into consideration the forces of interest. On the right, there is a depiction of the free-body-diagram of the object of interest as well as the y and x axis.

Free Body Diagrams (FBDs) are a pictorial representation of all of the external forces on an object. It starts as a simple dot representing your system. Then all of the forces are drawn, including relative size and direction. An axis must also be included to indicate which direction(s) are positive. Also, if a tilted axis is appropriate, such as in Inclined Planes then the tilted axis should be included as well as all relevant angles.

 

This picture depicts the steps that should be taken to create a free body diagram. The image shows a stop light held up by two poles on the left and right side with ropes attached to the stop light. First, sketch the image that the problem poses. Second, draw all of the possible forces acting on all of the objects which would be the stoplight and the two poles on the left and right side. third, draw a circle around the system of interest and erase all other forces that do not act on the object of interest. Fourth, break down each of the forces into its x and y components including the kind of force and the angle that it is acting on the object.

 

Translating FBDs is the most important tool you have for solving any problem involving forces. Translating a FBD involves using a FBD to break up all of the forces into their respective x and/or y components, identifying which components are going to be positive or negative, and summing up all the components in each given direction separately. You create an algebraic expression that is Newton's 2nd law with the aid of the FBD. This basic step will be the same for any force problem that we will ever do.

Videos

Pre-Lecture Videos

What is a Force? (5 min)

What is a Force? (5 min)

Types of Forces? (8 min)

Types of Forces? (8 min)

Steps to solving mechanics problems

Mechanics Steps (7min)

Free Body Diagram Fundamentals (15 min)

Free Body Diagram Fundamentals (15 min)

Web Resources

Text

 

Here is a chapter from the OpenStax textbook related to free body diagrams;

 

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This is a concise description of free body diagrams;

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Follow along in this interactive tutorial by W.W. Norton & Company about FBD;

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Here is a slide show demonstrating how to use free body diagrams with examples

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Other Resources

This link will take you to the repository of other content related resources.

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Videos

He shows you how to make a Flipping FBD (free-body diagram).

https://www.youtube.com/watch?v=pA9Uc_rJNiA

This video is very clear and discusses how to set up an easy to use free body diagram.

https://www.youtube.com/watch?v=BuPfDI7TyL0

Three part video series from the people at physics help.

https://www.youtube.com/watch?v=jHCsMXpYGAc

https://www.youtube.com/watch?v=eniPc9gUMy0

https://www.youtube.com/watch?v=8AcjOJAb8qA

Other Resources

This link will take you to the repository of other content related resources.

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Simulations

 

This PHet simulation allow you to view changing magnitudes of the force vectors in a FBD;

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This is a nice tool that will help you understand how to construct free body diagrams

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Here is a simple interactive to help you understand how to properly arrange force vectors,

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For additional simulations on this subject, visit the simulations repository.

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Demos

 

For additional demos involving this subject, visit the demo repository

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Practice

Fundamental examples

Draw the free body diagrams for the following systems.

1. The system of a picture of 2 cats in a box hanging from 1 vertical string in the center.

A representation of a system with two cats hanging in a box from one vertical string in the center.

 

2. The system of a picture of 2 cats in a box hanging from 2 strings at the given angles.

A representation of a system with two cats hanging in a box from 2 strings on the top two corners at two different angles denoted by theta one and theta two.

 

CLICK HERE for solutions.

Short foundation building questions, often used as clicker questions, can be found in the clicker questions repository for this subject.

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Practice Problems

BoxSand's Quantitative Practice Problems

BoxSand's Multiple Select Problems

BoxSand's Conceptual Problems

Recommended example practice problems 

Physics Classroom FBD w/ answers

For additional practice problems and worked examples, visit the link below. If you've found example problems that you've used please help us out and submit them to the student contributed content section.

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