Note on Posted Slides. These are the slides that I intended to show in class on Wed. Jan. 23 , 2013. They contain important ideas and questions from your reading. Due to time constraints, I was probably not able to show all the slides during class.
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[image from http://www.nytimes.com/imagepages/2006/11/28/business/28plug.ready.html]
Two things occur whenever work is done:
Unit of work:
or joule (J)
Unit of power
[Chart downloaded Jan.23 2013 from http://www.ontario-hydro.com/index.php?page=current_rates ]
[image downloaded Jan.23 2013 from http://www.sierraclubgreenhome.com/go-green/appliances/washers-and-dryers/ ]
Stored energy held in readiness with a potential for doing work
Potential energy due to elevated position
mass acceleration due to gravity height
A rectangular solid such as a domino has more gravitational potential energy when it is tipped up on its edge, because its centre of mass is higher
The energy is added to the domino by the work you do in tipping it up on its edge.
[image retrieved Jan.23 2013 from http://www.decodedscience.com/a-quick-explanation-of-mathematical-induction/1420 ]
If object speed is doubled kinetic energy is quadrupled.
Example: Applying the brakes to slow a moving car, work is done on it (the friction force supplied by the brakes distance).
CHECK YOUR NEIGHBOR
The work done in bringing a moving car to a stop is the force of tire friction stopping distance. If the initial speed of the car is doubled, the stopping distance is
A. actually less.
Ef = Ei
CHECK YOUR NEIGHBORSuppose the potential energy of a drawn bow is 50 joules and the kinetic energy of the shot arrow is 40 joules. Then
A. energy is not conserved.
Principles of a machine:
Work input work output
Output force output distance
This arrangement operates like a lever with equal arms— changes the direction of the input force:
This arrangement can allow a load to be lifted with half the input force:
More energy from the Sun hits Earth in 1 hour than all of the energy consumed by humans in an entire year!