Energy vs Power Sustainable Energy Jan 22 2007

Energy vs. Power Sustainable Energy Jan 22, 2007 Lecture by Joel Bettner

The Basics: Force • Force g – Accelerating a mass • What is keeping us on the earth? – Gravity accelerates us – We have mass – Gravity applies a force on our mass m F=mxg

The Basics: Work • Work – Force over a distance (i. e. a force causing something to move) Force Mass distance W=Fxd

Energy • Energy – The ability to do work • Potential Energy – How much potential energy does the mass have? – M x g x d = PE • Kinetic Energy – How much energy does the mass have? –. 5 x m x v 2 • Total Energy Conserved – T. E. = P. E. + K. E. Mass distance v

Energy • Energy – The ability to do work • Other forms of energy – Heat – Chemical – Nuclear

Power • Power is energy per time – Watch each horse – Which horse uses/produces more energy? – Which horse produced greater power? – James Watt (1782) • Coal mine horses lifting buckets of coal #1 d d M d #2 d M

Energy vs. Power • Ready to feel the power? – Break up into your groups • http: //cusustainableenergy. pbwiki. com/Groups – Grab one chair and go into the hall – WALK down the hall pushing a group member in the chair – Next, RUN down the hall pushing your group member

Energy vs. Power • Did you use more energy while walking or running? • Did you have a higher power production while walking or running?

Energy vs. Power • Think about your car – What is in your gasoline, energy or power? • What kind of energy is it? – What does the chemical energy in your gasoline produce • Power! Hence the “Horse Power” rating of a vehicle. • Kinetic Energy • Heat

Units • How do we measure force, energy, and power? Here are some common ways these are measured. – Force • English Units Pounds (lb) • Metric Units Newtons (N) – Energy • English Units Pound-Feet (lb-ft) • Metric Units Newton-Meters (N-m) Joule (J) – Power • English Units Horse Power (HP) 1 HP = 550 ft-lb/sec • Metric Units Watt (W) 1 W = J/sec

Questions and Discussion • Does anyone have any questions? • Can anybody think of common places/applications where the distinction between energy and power is visually evident? – I think of batteries • Battery in my car is MUCH larger than two 9 -volt batteries. However, my car battery is 12. 6 Volts. What do you think that means? • If discharged at the same power, which do you think would last longer? Why?