Physics Works

We began the class of May 14th by reviewing the concept of Work(W). The key ideas of this concept are:

• 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.

ex.

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

***Time does not change the amount of work done, it does however tie into POWER***

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!