Transcript What is Energy?

What is Energy?
• Physics Definition: The ability to do work
• Work: Force applied over a distance (W =f*d)
• Force: From Newton, force is the product of a
mass and its acceleration (F=ma) also known
as Newton’s second law.
• But this applies mostly to mechanics, the
study of the physics behind an object’s
motion
What is Energy?
• Thermodynamics: the study of the conversion
of heat energy into other forms of energy.
• Very important in the production of energy as
we will discuss it
• In themodynamics, work is defined as the
quantity of energy transferred from one
system to another without a change in its
amount of order (called entropy)
Units of energy
• Joules:
– The work done by a force of one newton (kg*m/s2)traveling
through a distance of one meter;
– The work required to move an electric charge of one coulomb
through an electrical potential difference of one volt; or one
coulomb volt, with the symbol C·V;
– The work done to produce power of one watt continuously for
one second; or one watt-second (compare kilowatt-hour), with
the symbol W·s. Thus a kilowatt-hour is 3,600,000 joules or 3.6
megajoules;
– The kinetic energy of a 2 kg mass moving at a velocity of 1 m/s.
The kinetic energy is linear in the mass but quadratic in the
velocity, being given by E = ½mv²
Everyday examples of the Joule
• the energy required to lift a small apple one meter straight
up.
• the energy released when that same apple falls one meter
to the ground.
• the energy released as heat by a quiet person, every
hundredth of a second.
• the energy required to heat one gram of dry, cool air by 1
degree Celsius.
• one hundredth of the energy a person can receive by
drinking a drop of beer.
• the kinetic energy of an adult human moving a distance of
about a hand-span every second.
• 100 joules are used by a 100 Watt light bulb every second
Power
• Power: the rate at which work is performed
– Or, the rate at which energy is transmitted
– Or the amount of energy expended per unit time
• P=E/t
• Measured in Watts:
• Other units:
– HP or horse power
– BTUs