# Work. Hard Work? True or false, did you do work on the object listed? True or false, did you do work on the object listed? You hold a book in one hand.

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Work

Hard Work? True or false, did you do work on the object listed? True or false, did you do work on the object listed? You hold a book in one hand while standing for 10 minutes.You hold a book in one hand while standing for 10 minutes. You start a resting ball rolling across a level table.You start a resting ball rolling across a level table. You move a heavy box from one desk top to another of equal height.You move a heavy box from one desk top to another of equal height. You carry a pen up a flight of stairs.You carry a pen up a flight of stairs.

Force over a Distance In physics, work is the force acting on object over a distance. In physics, work is the force acting on object over a distance. Forces acting on objects at rest do no work. Forces acting on objects at rest do no work.

Creating Motion Work is force acting over a distance. Changing motion requires a force: F = ma. Force is applied over a finite distance. Forces that change motion may do work. F v = 0 v > 0

Work in a Direction The force must act in the direction of the displacement to be work. The force must act in the direction of the displacement to be work. Force acts in this direction The object moves in this direction Not all the force is in the direction of motion.

Beginning and End Only the force acting in the direction of displacement counts towards work. Displacement considers the beginning and end points. Forces acting perpendicular to an objects motion do no work. Linear motion with perpendicular forces Uniform circular motion FGFG FGFG FNFN FNFN

Scalar Product Finding the component of a vector in the direction of another vector is called the scalar product. Finding the component of a vector in the direction of another vector is called the scalar product. AB A ||

Scalar Product Properties Perpendicular vectors always have a scalar product of zero. Perpendicular vectors always have a scalar product of zero. Scalar products can be found with unit vectors and components. Scalar products can be found with unit vectors and components. Scalar products can be mixed with vector addition. Scalar products can be mixed with vector addition. AB A || =0

Individual Force Work can be done by individual forces, or by a net force. Constant velocity has net force of zero. A net force of zero may include forces that are not zero. Force acting through a distance applies to separate forces. next F x FgFg F fr FNFN

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