PHYSICS 20 Work Conservation of Energy Quick lab

PHYSICS 20 Work

Conservation of Energy Quick lab 6 -1 pg 291 – Computer lab Law of Conservation of Energy: Energy cannot be created or destroyed, but it can be changed from one form to another. Can you think of any examples? We will look at the concept of mechanical energy: Which is the sum of potential and kinetic energies

Work – The Transfer of Energy is transferred when a force acts on an object, resulting in its displacement W = Fd So, in physics terms, am I doing work as a physics teacher? What about you as a student in your desks? What if I was holding a 30 kg box standing still? � I’m using energy, but am I doing work? � What is the work being done on in this case? If there is no displacement there is no work!

Work Symbol: W Formula: W = Fd Unit: N*m which is called a Joule (J) So really, work is any force over a certain displacement. The difficult part is, a Force can show itself in many ways.

Types of Work If work is done against gravity F=mg, therefore, W= mgh, h = displacement up. It can also work for the net force on a pulled object or with friction. These are all formulas you have experience with. Remember, always use the net force moving the object and forces can be negative. Let’s do an example: A 15. 0 kg object is lifted at a constant velocity from the floor to a height of 1. 50 m. How much work is done on the object?

Assignment One more example first! A 50. 0 kg box is pulled 11. 0 m along a level surface by a rope. If the rope makes an angle with the surface of 35. 0 degrees, and the force exerted through the rope is 90. 0 N, how much work is done on the box? Reading: Pearson Physics Pg 290 – 294 Questions: SNAP Pg 307 – 308 #’s 2 -7