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

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

Example 1 Normal Force F N F W Weight/Force due to Gravity A lab cart resting on a desktop

Example 2 A lab cart moving with a constant velocity across a surface FNFN FWFW Applied Force F A Friction f

Example 3 A lab cart accelerating to the right across the floor FNFN FWFW FAFA f

Example 3 A tetherball while swinging at a constant speed around a pole FWFW 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.

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