Work is the product of an applied force and the displacement of an object in the direction of the applied force.- Work is a scalar quantity
- The SI unit of Work is Joules (J)
- If there is no applied force, there will be no work done
- If there is no displacement there will be no work done
We then proceeded to do some example problems.
A boy pulling a wagon is exerting a force of 20.0 N at an angle of 35 deg to the horizontal. If he pulls it 100.0 m along the ground, calculate the work done.
Cos35 = Fax W = Fd
20.0N W = (16.38 N[fwd]) (100.0m[fwd])Fax = 16.38 N [fwd] W = 1600J
We also learned that work can be calculated from an applied force vs displacement graph by finding the area underneath the graph. However, estimation is sometimes needed when a graph is curved.
We continued with the day's lesson by learning about Energy (E)
- Energy is the ability to do work
- When work is done, energy is transferred from one object to another
- Unit is Joules
- An increase of Energy of an object means that the work done on it will be positive and vice versa
- Not all Energy is used when it is converted from one form to another
- Energy efficiant products minimize lost Energy
What is Power (P)?
- The rate at which work is done
- The rate at which energy is used
- SI unit is the watt (W)
- Power = work
- time
- The more time it takes to complete a task, the less power is had.
Ex:
A man does 120 J of work in lifting a box from the floor to the table. If it took 2.0 s to perform the task what is his power?
W = 120 J P = W P = 120 J P = 60. W
T = 2.0 s T 2.0s
P = ?
And thus concludes the class that took place on Monday May 14th, 2012
<-- work done!
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