4.2 A Short Catalog of Forces

Drag

(Resistive Force) The force of a fluid on a moving object (points opposite the direction of motion) (*Neglect air resistance unless you are asked to include it*)

Normal Force

A force exerted by the surface on an object in a direction perpendicular to the surface of contact

Thrust

A force opposite the direction in which the exhaust gas is expelled

Friction

A force that opposes motion between two surfaces that are in contact (*parallel to the surface*)

Kinetic Friction

Acts as an object slides across a surface, opposes motion, points in the direction opposite the direction of the object's motion

Spring Force

Can either represent a push (compressed) or pull (Stretched)

Static Friction

The force that keeps an object stuck on a surface and prevents its motion relative to the surface, points opposite the direction in which the object would move if there were no friction

Weight

The gravitational pull of the Earth on an object on or near the surface of the Earth. (Agent is entire Earth pulling on an object) (*Always points vertically downward*)

Tension Force

When a strong or rope or wire pulls on an object (direction of tension force is always in the direction of the string or rope) (contact force)