1. Free Body Diagrams
A Free Body Diagram (FBD) is a visual representation of all the forces acting on a single object
FBDs are extremely powerful problem solving tools that bridge the gap between qualitative analysis and a quantitative mathematical representation

2. Drawing an FBD…
A simple dot can be used to represent the object in question
Identify the forces acting ON that object only
Draw one arrow to represent each force acting ON the object
All arrows should be drawn from the dot or the center of the object
The arrows point in the direction of the force.
The length of the arrow represents the relative magnitude of the force…ie longer arrows = larger force

3. Example 1 A block of wood resting on a desktop Normal Force FN FW
Weight/Force due to Gravity

4. Example 2
A block of wood moving with a constant velocity across a surface FN FW
Applied Force FA
Friction f

5. Example 3 A block of wood accelerating to the right across the surfaceFN FW FA f

6. Example 4
A block of wood accelerating to the right when pulled by a rope at an angle FN FW
Tension T f

7. Example 5
A tetherball while swinging at a constant speed around a pole FW
Tension T
Notice there is nothing in the original description that says the tetherball is being hit. A diagram for the ball as it is being hit would show an additional force acting on the ball.

8. Example 4
Try it… Draw a FBD and write the 2nd law equations for a lawn mower being pushed at a constant speed