CHAPTER
5
Work and Energy
http://www.physicsclassroom.com/Class/energy/energtoc.html
Units
•
Work Done by a Constant Force
•
Work Done by a Varying Force
•
Kinetic Energy, and the Work-Energy Principle
•
Potential Energy
•
Conservative and Nonconservative Forces
•
Mechanical Energy and Its Conservation
•
Problem Solving Using Conservation of Mechanical Energy
•
Other Forms of Energy; Energy Transformations and the Law of Conservation of
Energy
•
Energy Conservation with Dissipative Forces: Solving Problems
•
Power
Work Done by a Constant Force
The work done by a constant force is defined as the
distance moved multiplied by the component of the
force in the direction of displacement:
•
This gives no information about
–
the time it took for the displacement
to occur
–
the velocity or acceleration of the object
•
Work is a scalar quantity
•
The work done by a force is zero when the force is perpendicular to the displacement
–
cos 90° = 0
•
If there are multiple forces acting on an object, the total work done is the algebraic sum of
the amount of work done by each force
•
Work can be positive or negative
–
Positive if the force and the displacement are in the same direction
–
Negative if the force and the displacement are in the opposite direction
In the SI system, the units of work are joules:
As long as this person does not lift or lower the bag of groceries, he is
doing no work on it. The force he exerts has no component in the
direction of motion.
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