1. Energy and Power We think about it all the time…

2. Work  Work = Force * Distance  Units: Force  Newtons Distance  meters  Hence Work units  Nm  A Nm is defined to be a Joule.  Work is a form of energy.

3. James Prescott Joule  James Prescott Joule (1818 –1889) was an English physicist and brewer.  Joule studied the nature of heat, and discovered its relationship to mechanical work.  This led to the theory of the conservation of energy.  The unit for energy, the joule, is named after him.  He worked with Lord Kelvin to develop the absolute scale of temperature and found the relationship between electric current through a resistance wire and the heat dissipated, which is now called Joule's law.

4. Conservation of Energy  Joule’s work led to the discovery of the  conservation of energy.  To say that energy is conserved is to say that it may change form, but I cannot be created or destroyed.  Well, OK… uh, let’s qualify that.  Energy cannot be created or destroyed “by ordinary means.” Yeah, that should cover it.

5. Power  Power = Work/Time  Units: Work  Joules Time  seconds  Hence Power units  J/s  A J/s is defined to be a watt.  Power is the rate at which work is done.

6. Kinetic energy  KE = ½mv 2  Units: Joules of course, since it is energy of motion.  Calculate the KE of a 2 kg ball moving at 5 m/s. (White boards)  KE = ½mv 2 = (½)(2kg)(5 m/s) 2 = 25 Joules

7. Potential energy  There are many types of “potential energy,” which is the potential to do work.  Gravitational PE is energy of position. As we raise an object above the earth it gains the gravitational potential to do work.  If we then “drop” it from that height, it converts to KE.  PE = mgh  Units: Joules of course, since it is energy of position.  Calculate the PE of a 2 kg ball raised to a height of 5 m. (White boards)  PE = mgh = (2kg)(9.8m/s 2 )(5m) = 98 Joules