Energy is a property that enables something to do work
Energy has various forms (kinetic, potential, rest energy)
Kinetic energy is the energy of a moving object
KE = ---------
It takes ~1000 N (or ~ 225 lbs) to hit a nail and drive it 5 mm into a surface.
Potential energy is a capacity of doing some work
Potential energy is the energy of position
Gravitational Potential Energy
W = Fd = mgh = PE (potential energy)
PE is relative!
PE of a 1000-kg car at the top of a 50-m multilevel parking lot is:
mgh= (1000 kg)(9.8 m/s2)(50 m)=490 kJ
Mass and Energy are related to each other and can be converted into each other.
The rest energy of a body is the energy equivalent of its mass.
E0 = m0c2
E0 (m=1 kg) = 1 kg x (3 108)2 (cm/s)2 ~ 1017 J
PE (m=1 kg, h=9 km) = mgh = 1 kg x 9.8 m/s2 x 9000 m ~ 105 J
Many mechanical processes involve interchanges between KE, PE, and work.
Energy exists in some other forms: chemical energy, heat energy, radiant energy, etc.
Energy cannot be created or destroyed.
It can only be changed from one form to another.
The above statement is called the law of conservation of energy
Light and Atomic Structure
Light and its properties
Interaction between Light and Matter
Light is a form of energy, radiative energy
1 Watt = 1 Joule/sec
Light has color
A prism split light into a spectrum (rainbow of colors)
Light travels with a speed of c = 300,000 km/s
Transmission (passing through)
Light behaves as both a particle and a wave
Light particles are called photons, which can be counted individually.