Energy
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Energy
Energy is the capacity to do work or produce heat.
Types of Energy
1. Kinetic Energy (KE)
Energy possessed by a body because of its motion.
KE =
1 2
mv2
2. Potential Energy (PE)
Energy possessed by a body because of its relative position.
PE = mgh
m: Mass of the body
g: Acceleration due to gravity. For Earth, g = 9.8 m/s2
h: Height of the body
3. Internal Energy (U)
Total kinetic energy and potential energy of all the molecules in the body/system.
ΔU = Q - PΔV
Q: Heat transferred to the body or system
P: External Pressure applied on the body or system
V: Volume of the body or system
Total Energy (E)
ΔE = ΔKE + ΔPE + ΔU = Q + W
ΔU: Change in Internal Energy
ΔKE: Change in Kinetic Energy
ΔPE: Change in Potential Energy
Q: Heat transferred to the system
W: Work done by the system
For a stationary process: ΔE = ΔU = Q + W
Law of Conservation of Energy
Energy can neither be created nor destroyed; energy can only be transferred or converted from one form to another.
ΔEsystem = -ΔEsurrounding
If energy is lost by the system, then it is absorbed by the surroundings. If energy is absorbed into a system, then that energy was released by the surroundings.
Esystem: Total energy of the system. System is the body/environment under study.
Esurrounding: Total energy of the surrounding. Surrounding is everything other than the system.
Types of Kinetic Energy
1. Translational Kinetic Energy
Energy possessed by a body because of its linear motion.
2. Rotational Kinetic Energy
Energy possessed by a body because of its rotational or spin motion.
3. Vibrational Kinetic Energy
Energy possessed by a body because of its vibrational motion.
Types of Potential Energy
1. Gravitational Potential Energy (Ug)
Energy possessed by a body because of its position in a gravitational field.
Ug = −
GMm r
G: Gravitational Constant = 6.67 × 10-11 m3/kg·s2
m: Mass of the body
M: Mass of the attracting body
r: Distance between their centers
2. Elastic Potential Energy (Ue)
Energy possessed by a body because of its stretched or compressed position.
Ue =
1 2
kx2
k: Spring Force Constant
x: String Stretch Length. It will be negative if compressed.
Heat Energy
Energy transferred due to temperature difference between the systems.
It causes temperature changes in the system.
Work Energy
Energy transferred due to force applied on the system. It is the energy transferred other than heat.
It causes displacement of the system.
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