What is Energy?
Energy is the ability to do work, usually against some force.
When you climbed the stairs to this class, you had to do work
against gravity to get up here. That required an expenditure
of energy.
But, you only borrowed this energy. You can get it back if you
jump back down to the atrium floor (not recommended).
Energy comes in many forms, kinetic, potential (stored), heat,
etc. Energy is always conserved. It is not created or destroyed
but is just transformed from one form to another.
Common Types of Energy |
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Type of Energy | What it is |
- Kinetic Energy (KE)
- Gravitational Potential Energy (GPE)
- Chemical Potential Energy (CPE)
- Elastic Potential Energy (ELPE)
- Thermal Energy (H)
- Electromagnetic Radiation (ER)
|
energy associated with motion
energy associated with position in a gravitational field
energy associated with the bonding of molecules in
a chemical
"spring energy" - a form of stored energy
heat dissipation
release of photons
|
Kinetic and Potential Energy:
Throwing a ball into the air represents a situation in which the total
energy is fixed and there is a continous transformation from kinetic
energy to potential energy.
- When the ball is on the ground there and not moving there is
no potential energy or kinetic energy
- when the the ball is tossed into the air it will reach a maximum
height which is determined by how much kinetic energy it has (air
resistance is important however)
- when the ball reaches its maximum height its velocity is 0 and
all of the energy in the system is potential energy
- as the ball falls to the ground that potential energy is
converted to kinetic energy
- Some amount of energy is loss due to air friction which then
heats up the air (just a tiny bit).
Most Energy loss is via heat. This
is generally not released. Heat loss is usually irrecoverable.
This is a principle feature of the field of thermodynamics that
we will discuss later.
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But what is heat? Heat is infrared radiation.
How do you measure heat?
Temperature is a measure of heat indirectly but does directly measure
the energy loss of some thermodynamic system.
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