 # Chapter 10: Work, Energy, and Simple Machines

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Chapter 10: Work, Energy, and Simple Machines

Work No it’s not your job!
Work is the product of force and the distance an object moves in the direction of force Scalar quantity- no direction Measured in Joules A JOULE is 1 newton of force times one meter of movement The object must MOVE or there is no work, only force

Work Work only occurs if the force and displacement are in the same direction Increasing the force or the displacement, increases the work done on an object FORMULA FOR WORK W = Fd Work = Force times displacement Example problem #1 Practice problems #1-3

Work and the direction of force
Force must be exerted in the direction of motion for work to be done If the force is perpendicular to the motion- NO WORK IS DONE!!! The object that exerts the force does the work

Work and angles of force
What happens when the force is at an angle to the motion? Use the amount of force acting on the direction of motion Use the formula W = Fd(cos) to determine the amount of force in the direction of motion If the work is negative- the object is doing work on another object If the work is positive- work is being done on the object

Work and angles of force
The effect of doing work is the transfer of energy from one object to another Work is the mechanical transfer of energy

Steps for solving work problems
Carefully check the forces acting on the object You may use vector diagrams to do this Determine the displacement and any angle between the force and the direction of motion Check the sign (+ or -) by determining the direction energy is transferred If the sign is positive energy has increased If the sign is negative energy has decreased

Practice Example problem #2 Practice problems #5-7

Power Work does not consider time
Work to move a stack of 10 objects 1m is the same whether you move each object in 2 seconds or 10 seconds. POWER is the rate work is done- more power is required to move the stack of 10 objects in 2 seconds than is required to move the same stack in 10 seconds Power is work done divided by the time it takes to do the work P = W/t Measured in watts or kilowatts 1 watt = 1 joule per second

Practice Example #3 Practice problems 9-11 Lab- Page 204

Simple Machines