Forces and Free Body Diagrams

1. Forces and Free Body Diagrams

2. Kinematic Forces

3. Example 1 Draw a FBD of the following scenarios: • A pen sitting on a table. • A rope connected to a crane raising a piano vertically upward at a constant speed. • A suitcase being rolled across the floor at a constant velocity with a force applied at 20° above the horizontal. • A dresser that is being pulled to the right up a ramp into a delivery truck by a cable parallel to the ramp; the ramp is 14° above the horizontal.

4. Example 2 Draw three FBDs depicting the forces of an object as it changes from free-fall to terminal velocity.

5. Net Force • Often there is more than one force acting on an object. To describe the effect of all the forces acting on an object, physicists determine the net force. Sometimes the net force is referred to as the total or resultant force. Fnet = Σ Facting on object Where ΣF1 = F1 + F2 + F3 + … • Where F1 , F2 ,F3 are all the forces acting on a body. • Remember that an appropriate vector method will be required to solve this force problem. • Note that if the net forces acting on an object equals zero, we say that the object is in static equilibrium

6. Example 3 Two tractors pull a large rock on a construction site with a net force of zero on the rock. Tractor 1 exerts a force of 1.2 x 104 N [E 120 N] on the rock, and tractor 2 exerts a force of 1.2 x 104 [E 120 S]. Calculate the force of friction acting on the rock. Assume the rock is at rest.