Forces Force = a push or pull that results from an interaction between two objects Evidence of Interaction = change in: – Volume-- Sound-- Motion – Shape-- Color-- Tempo – Size-- Pitch-- Brightness – Texture-- Speed-- Temperature – Illumination-- etc.

Two Categories of Force Contact forces When objects physically touch – Applied (push/pull) – Friction/Air Resistance – Normal – Tension – Elastic Non-contact forces Action occurs at a distance – Gravitational – Electrostatic – Magnetic 2

Applied Force When one object pushes or pulls on another Direction: Depends on application

Force of Friction/Air Resistance When one object rubs against another Direction: opposite of motion

Normal Force The force pushing up on an object from the contact surface. Direction: perpendicular to surface

Tension Force The force exerted by a loaded string, rope, wire, cable, etc. Direction: depends on the position of the load

Elastic Force The force exerted by an object returning to its original shape. Direction: depends on the position of the load

Gravitational Force Attraction between two objects (depends on mass) Direction: pulls toward the Earth

Electrical Force The attractive or repelling force between two charged objects Direction: depends on the relative position of objects.

Magnetic Force The attractive or repelling force between two objects with a magnetic field Direction: According to magnetic field (+ is attracted to -)

Representing Forces Drawing Force Diagrams: – Use a dot to represent the center of the object forces are acting on. – Use arrows to represent Direction Relative amount/strength – Label Type of Force (see notations on the next slide) – Label the “on ____, by ____” to give your understanding of how the objects are interacting

Label Notations Contact forces F a : F Applied F f : F Friction F n : F Normal F t : F Tension F el : F Elastic Non-contact forces F g : F Gravitational F E : F Electrostatic F m : F Magnetic 12

Example of a Force Diagram