Physics 9/20

Physics 9/29

Open Ended

Journal - Chop Wood, Carry Water

Free-Body Diagram

a physical representation that shows the forces acting on a system.

Guidelines for drawing Free-Body Diagrams

• The free-body diagram is drawn separately from the sketch of the problem situation.

• Apply the particle model, and represent the object with a dot.

• Represent each force with an arrow that points in the direction the force is applied. Always draw the force vectors pointing away from the particle, even when the force is a push.

Guidelines for drawing Free-Body Diagrams (cont.)

• Make the length of each arrow proportional to the size of the force. Often you will draw these diagrams before you know the magnitudes of all the forces. In such cases, make your best estimate.

• Label each force. Use the symbol F with a subscript label to identify both the agent and the object on which the force is exerted.

• Choose a direction to be positive, and indicate this on the diagram.

Example 1

• What represents the system?

• Is it a balanced or unbalanced force?

• Notice the positive direction is noted

• .Notice the how the vectors are labeled.

Example 2

• What is the system?

• How many agents are acting on the system?

• 
  

• 
  

Combining Forces

What happens if you and a friend each pus a table and exert 100 N of force on it?

Combining Forces

• Scenario 1 - Both push with 100 N in opposing directions

• Scenario 2 - Both push with equal force of 100 N in the same direction.

• One pushes with a force of 200 N and the other pushes with a force of 100 N in opposite directions.

Net force

This image also shows us the net force, or the vector sum of all the forces on an object.

Open Ended

Exit Ticket - What is a free body diagram?

Practice Problems

Go to Google Classroom and work on the practice problems for today.