1. Work, Power and Energy Chp 10 and 11

2. Some Terms  Work  Exerting a force over a distance  Energy  The ability to do work (or change the world around you)  Kinetic energy  Energy due to motion  Potential energy  Energy due to position or composition  Work-energy theorem  work is required to change KE  Power  The rate at which work is done

3. Work  Must be exerted over a distance  If nothing moves, no work was done on THAT object (could still be done on you)  Need to use the net force to calculate work  All the vector addition rules still apply  SI unit is Joule (J)  Work is a vector, since force and displacement are vectors  Can be negative, which means the work is being done by the object rather than on it

4. Power  If the same amount of work is done more quickly, then more power is exerted  Its harder to do a job quickly than it is to do the same job more slowly  SI unit is Watts (W)  Often we use kilowatts since watts are such a small unit

5. Simple Machines  A device that makes work easier, either by changing the distance or direction that a force is exerted  It doesn’t make the work less  If you increase the distance a force is exerted, than less force is needed to do the same amount of work  The machine imparts no energy of its own

6. 6 Types of Simple Machines  Inclined plane  Ex. ramp  Lever  Ex. crowbar  Wheel and axel  Ex. tire  Pulley  Ex. Well bucket  Wedge  Ex. ax  Screw  Ex. Wood screw

7. Calculating the Benefits of Machines  Mechanical advantage  Compares effort and resistance forces  Ideal mechanical advantage  Compares effort and resistance distances  Efficiency  Compares how much of the input work gets translated to output work  Often work is lost to heat due to friction

8. Compound Machines  Result from a combination of 2 or more simple machines  The resistance force of one machine becomes the effort force of another  Like dominoes  However, the efficiency is less because friction increases with each additional machine

9. Conservation of Energy  Energy can change forms and be passed between objects, but it cannot be created or destroyed  Forms of energy:  Kinetic  Elastic potential energy  Thermal energy  Gravitational potential energy

10. Collisions  2 types:  Elastic  KE is conserved in the collision  Occurs between hard objects  Inelastic  KE is lost in the collision due to deformation, heat and sound  Occurs between soft or sticky objects  Energy is still conserved, its just not all kept at KE