# PHYS 2211 Module 5.7

## Drawing Free-Body Diagrams 5.7 Drawing Free-Body Diagrams

### Learning Objectives

By the end of this section, you will be able to:

• Explain the rules for drawing a free-body diagram
• Construct free-body diagrams for different situations

### Tactics for Drawing a Free-Body Diagram

• Identify all forces acting on the object.
• Draw a coordinate system.  Align one of the axes with the acceleration of the object.
• Represent the object as a dot at the origin of the coordinate axes. This is the particle model.
• Draw vectors representing each of the identified forces. Be sure to label each force vector.
• Draw and label the net force vector Fnet. Draw this vector beside the diagram, not on the particle. Then check that Fnet points in the direction of the acceleration. Or, if appropriate, write Fnet = 0. Discuss!

Consider how you would answer these questions. Then bring this to class for a group discussion. When you apply an upward force of magnitude F to a block of mass 2.00 kg, the block accelerates upward at 3.00 m/s2. You can ignore any forces exerted on the block by the air. Rank the following forces in order of their magnitude, from smallest to largest.

• the force F
• the net force on the block
• the gravitational force on the block Practice!