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SPH4C: Physics, Grade 12, College Preparation

Unit 1: Motion and Its Applications

Activity 4: Force, Free-Body Diagrams, and Net Force

Content


Free-Body Diagrams

To help visualize and solve problems involving forces, it is useful and often necessary to draw free-body diagrams.

Free-body diagrams are diagrams in which the forces acting on an object in a given situation are drawn on the object, free of its surroundings.

Points to remember when drawing a free-body diagram:

Example Icon Example

As you are sitting on a chair, there are two forces acting on you. There is the force of gravity acting downward and the force of the chair upward on you, e.g., the normal force. These forces are shown acting on the lady sitting on a chair below. The free-body diagram (FBD) is shown to the right.

This is a diagram showing the forces acting on a girl sitting on a chair and the appropriate free-body diagram for this situation.

Practice Icon Check Your Understanding

Draw free-body diagrams for the red book in each of the following situations. Check your answers by holding your mouse over the image to see the correct FBD.

  1. a falling book

    This image shows a FBD for a book in free-fall.


  2. a book sitting on a desk (FBD is for the book)

    This image shows a FBD for a book resting on a desk.


  3. a book being pushed (and accelerating) across a desk

    This is a sketch of a book being pushed across a table.

Resources Icon Resources

  1. Shockwave Physics Video – Free Body Diagram Activity
  2. Free Body Diagram Tutorials/Quizzes at the University of Guelph

Unless otherwise indicated, all images in this activity are from the public domain or are © clipart.com or Microsoft clipart and are used with permission.
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