Physics: Energy, Thermodynamics, Fluids, & Solids
1.Energy
Here c is the speed of light = 3 x 108 m/s
Conservation of energy: In a closed system, the initial mechanical
energy (ME) equals the final mechanical energy:
K Ei + P E i=K Ef + P E f
If there is a net external force on the system, energy is not conserved,
instead the final ME could be more or less than the initial ME.
M E i+ W external =M E f
Work (W) and energy are measured in Joules (J)
Energy added: Work is positive
Energy removed: Work is negative
Examples:
Energy conserved: Ball rolls down a hill without friction use mgh=½ mv 2
Energy not conserved: Ball is pushed down a hill (Energy added so +W)
, Physics: Energy, Thermodynamics, Fluids, & Solids
Energy not conserved: Ball rolls up a hill with friction (Energy removed so -
W)
2.Momentum and Collisions
Momentum:
p=mv
Momentum is always conserved so the initial momentum of a system
equals the final momentum of the system:
m1 v 1 i+ m2 v 2 i=m1 v 1 f +m2 v 2 f
Types of collisions:
Elastic: Energy is conserved, momentum is conserved
Perfectly Inelastic: Objects stick together, mechanical energy is
reduced
Inelastic: Objects do not stick together, mechanical energy is reduced
Superelastic: Mechanical energy increases
For perfectly Inelastic collisions use the derived equation:
m A v Ai +mB v Bi =v f (m A +mB )
Remember: Velocity is a vector, so if two
objects are going in opposite directions, one
velocity must be negative.
, Physics: Energy, Thermodynamics, Fluids, & Solids
3.Temperature, Heat, and Thermal Energy
Thermal energy: The sum of all the particles’ energies in an object
(Joules)
Temperature: The average KE of the particles in an object (Celsius or
Kelvin)
Thermal energy increases as number of particles increase; temperature
is not affected by number of particles because it is the average KE while
thermal energy is the sum of energies.
Temperature has two widely used scales: Degrees Celsius or Kelvin
Celsius (C°) and Kelvin (K) are linearly related, so if C° increases by 2, K also
increases by 2.
Relationship between C° and K:
K=° C+ 273.15
C °= K−273.15
Absolute Zero: An impossible temperature at 0 K where matter does not exist
1.Energy
Here c is the speed of light = 3 x 108 m/s
Conservation of energy: In a closed system, the initial mechanical
energy (ME) equals the final mechanical energy:
K Ei + P E i=K Ef + P E f
If there is a net external force on the system, energy is not conserved,
instead the final ME could be more or less than the initial ME.
M E i+ W external =M E f
Work (W) and energy are measured in Joules (J)
Energy added: Work is positive
Energy removed: Work is negative
Examples:
Energy conserved: Ball rolls down a hill without friction use mgh=½ mv 2
Energy not conserved: Ball is pushed down a hill (Energy added so +W)
, Physics: Energy, Thermodynamics, Fluids, & Solids
Energy not conserved: Ball rolls up a hill with friction (Energy removed so -
W)
2.Momentum and Collisions
Momentum:
p=mv
Momentum is always conserved so the initial momentum of a system
equals the final momentum of the system:
m1 v 1 i+ m2 v 2 i=m1 v 1 f +m2 v 2 f
Types of collisions:
Elastic: Energy is conserved, momentum is conserved
Perfectly Inelastic: Objects stick together, mechanical energy is
reduced
Inelastic: Objects do not stick together, mechanical energy is reduced
Superelastic: Mechanical energy increases
For perfectly Inelastic collisions use the derived equation:
m A v Ai +mB v Bi =v f (m A +mB )
Remember: Velocity is a vector, so if two
objects are going in opposite directions, one
velocity must be negative.
, Physics: Energy, Thermodynamics, Fluids, & Solids
3.Temperature, Heat, and Thermal Energy
Thermal energy: The sum of all the particles’ energies in an object
(Joules)
Temperature: The average KE of the particles in an object (Celsius or
Kelvin)
Thermal energy increases as number of particles increase; temperature
is not affected by number of particles because it is the average KE while
thermal energy is the sum of energies.
Temperature has two widely used scales: Degrees Celsius or Kelvin
Celsius (C°) and Kelvin (K) are linearly related, so if C° increases by 2, K also
increases by 2.
Relationship between C° and K:
K=° C+ 273.15
C °= K−273.15
Absolute Zero: An impossible temperature at 0 K where matter does not exist
