Milk production at a diary farm was low so the farmer wrote to the local university asking for help from academia. A multidisciplinary team of professors was assembled and two weeks of intensive on-site investigation took place. The scholars then returned to the university, notebooks crammed with data, where the task of writing the report began. Shortly thereafter the farmer received the write-up, and opened it to read on the first line: “Consider a spherical cow …”

What is ‘the ability to do work’? To DO anything, energy is required. BUT, the point to grasp is Energy isn’t so easy to define. Other definitions: - Measure of ability - Capacity to produce heat - E=mc 2 Energy

Definitions  Work  Force acting over a distance.  A measure of accomplishment.  Doing.  Power  Rate of energy use – energy/time  units: Watts (W), horsepower (hp)  Efficiency  (what you get out)/(what you put in)  Potential energy – stored energy.  Kinetic energy – energy associated with motion.  There are an incredible number of overlapping classifications of energy. Units of energy: Joule (J), btu, Calorie

More definitions  Thermal energy - kinetic energy of molecules  We think of this as heat.  Radiation (electromagnetic energy)  This includes X-Rays, light, radio waves, cell phone communications, microwaves, and more  This stuff is very cool.  Electrical energy – kinetic energy of charges  Mechanical energy – energy associated with moving parts  Chemical potential energy – energy stored in molecular bonds  Nuclear energy – energy stored in the nucleus of atoms

Energy ‘Laws’  Conservation  Energy can be created or destroyed, it can change forms but it always exists.  1 st Law of Thermodynamics E earth E in E out E in + E earth – E out = constant ThermalMechanical+ Thermal Mechanical Thermal  Conversion of thermal energy to mechanical energy  Can’t be 100% efficient  2 nd Law of Thermodynamics

Mechanical vs. Muscular Energy  The incredible increase in economic and technological advances of the ‘modern’ world were brought about by humankind’s switch from muscular to mechanical energy.  How do they compare?  Let’s look at an example that may give us all a better grasp of energy.  Example – my daily commute  Niwot to CU

Muscular Energy (in honor of bike week)  If I bike, I am using muscular energy.  How much?  260 kJ  Where does the muscular energy come from?  Food (potential energy of food molecules)  Our bodies convert food energy to muscular energy with ~20% efficiency.  SO, I need to input 1300kJ to get to work on muscular energy.

Mechanical Energy  If I drive to work, I am using mechanical energy.  How much?  Let’s skip this step and directly calculate the amount of energy in the amount of gasoline that I consume.  I use ~1 L to get to work.  So, I use 48,000 kJ of energy to drive to work.  I use 37x more energy driving than biking.  BUT, when driving, I get there faster (3x) and I can carry more stuff.

Another example: How does my toaster do work?  Coal is mined in Wyoming and shipped via rail to Cherokee Station in Denver.  The chemical potential energy in coal is converted to thermal energy and other less energetic molecules. (We call this process combustion.)  The thermal energy is converted to mechanical energy in a steam turbine.  The mechanical energy is converted into electrical energy in a generator.  The electrical energy, which is easy to move, is sent to my house on wires.  The electrical energy reaches my toaster through it’s cord and is converted into thermal energy via a big resistor.  The thermal energy warms my toast.

Last points  Net energy use:  I have also heard this concept called ‘lifecycle energy’.  There is ‘other’ energy involved with me driving or biking to work.  Energy required to build my bike.  Energy required to build the paths that I bike on.  Energy required grow and process the food that I need as fuel.  Energy required to process and get water to me so I can ride my bike.  All the energy required needs to be included when developing comparisons.  In any energy conversion process, what happens to the energy that is converted to the useful form?  Combustion  What happens to molecules with lower internal energy?  What happens to the thermal energy not converted to mechanical energy?  Metabolism of food