NOTES 3: Drawing a Force Diagram (AKA Free body Diagram) Force & Motion NOTES 3: Drawing a Force Diagram (AKA Free body Diagram)

WHAT IS A FORCE DIAGRAM? A simple, labeled diagram that shows the forces acting on an object as arrows that indicate the magnitude and direction of the force. 2N 5N

Newton Balanced forces Unbalanced forces VOCABULARY Force diagrams require a knowledge of the following: MAGNITUDE DIRECTION NET FORCE And a review of… Newton Balanced forces Unbalanced forces

MAGNITUDE The amount of force applied to an object; the higher the force, the greater the magnitude

DIRECTION Um, duh? The place towards which an applied force is pushing or pulling an object On a force diagram, the direction is indicated by an arrow. The arrow points in the direction the force is moving the object.

The combined force (magnitude and direction) acting on a object. NET FORCE The combined force (magnitude and direction) acting on a object.

the SI (standard international) unit for force Equal to: 1 kg x 1m/s2 NEWTON (N) the SI (standard international) unit for force Equal to: 1 kg x 1m/s2

BALANCED FORCES When the magnitude and direction of more than one force acting on an object results in a net zero force

UNBALANCED FORCES When the magnitude and direction of more than one force acting on an object results in a net force unequal to zero

HOW TO DRAW A FORCE DIAGRAM Draw a square, rectangle, or circle to represent the object the force will be acting upon. Label the object!! Draw ONE arrow for each force that is acting upon the object. The size of the arrow reflects the magnitude of the force. The direction of the arrow shows the direction that the force is acting. Label each arrow you’ve drawn with the magnitude of the force.

PRACTICE 1 A book is resting on a tabletop. The book sits on the table with 5N worth of force.

PRACTICE 1 What is the net force? Does the book move? 0 (zero) No (the book is at rest)

PRACTICE 2 Marissa and Nadia are playing tug of war. Marissa pulls the rope with 3N of force and Nadia pulls the rope with 4N of force.

PRACTICE 2 What is the net force? rope 4N 3N What is the net force? 1N to the right (the 3N of force in opposite directions cancel other out leaving only 1N to the right) Who wins the tug-of-war? Nadia

ALRIGHTY THEN… IF MORE THAN ONE FORCE ACTS ON AN OBJECT ALON G A STRAIGHT LINE, THE FORCES WILL REINFORCE OR CANCEL EACH OTHER OUT – DEPENDING ON THE DIRECTION AND MAGNITUDE OF THE FORCES.

UNBALANCED FORCES In which examples were their nonzero net forces? Unbalanced forces result in nonzero net forces that will cause a change in speed or direction (or both) of the object’s motion. In which examples were their nonzero net forces? What happened to the speed/direction in those examples?

REINFORCE 10N NET FORCE : 15N to the right 5N The net force is twice what either force would be alone. They combine forces (Ha Ha!) because they are acting upon the object in the same direction.