CHEM H90 Lecture Notes - Lecture 4: Roygbiv, Electromagnetic Spectrum, Heat-Ray
Lecture #4
• outline
o classical physics
o planetary motion and Newton’s laws
o light is a wave
• classical worldview
o particles (or planets)
▪ energy
▪ skateboarding
▪ solar system
▪ bound and free
o light
▪ waves
▪ wavelength and frequency
• Newton’s world: classical mechanics
o classical = 19th century
o if you know forces and initial conditions, can calculate what happens forever after
o for gravity, F= G m M/r^2
o m is mass of one body, M is other
o G is universal gravitational constant
o r is distance between bodies
o gravitational force is always attractive
▪ force is positive
▪ always brings things together
• better way to think about it
o if no outside forces act, total energy is conserved
o 2 types of energy: kinetic and potential
o kinetic energy is mv^2/2, always positive
o for gravity between two bodies, potential energy is –GmM/r, always negative
o total energy = kinetic energy + potential energy
• kinetic energy
o energy due to motion of particles
o KE = kinetic energy = mv^2/2
o if I double the mass, KE changes how?
▪ KE doubles
o If I halve the speed, KE changes how?
▪ KE reduces by 1/4
o KE is never negative
• gravitational potential energy near Earth’s surface
o for small objects near Earth’s surface,
o PE = mgh
▪ m is mass of object
▪ g is acceleration due to gravity, about 10 m/s^2
▪ h is height above surface
o how does PE change with height?
▪ PE increases
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