Physics of Astronomy Tuesday, winter week 7 (21 Feb.06) Math-A: Giancoli Ch.7&8 – Work and Energy Discuss rotational dynamics lab Math-B: Giancoli 11, Raff Ch : Intro to QM HW setup Dr. Neal Hurlburt visits Wednesday – lunch discussion 1:00 here Looking ahead: quiz this Thus.

Relationship between force and work/energy Examples of energy … Work done = force. displacement in the same direction Dot product: product of PARALLEL components of vectors Do Ch.7 (p.171) Forces & Work #4, 6, 7, Dot products # 21, 25

7-3: Work done by a varying force Example: Spring obeys Hooke’s law: F = -kx Do Ch.7 (p.172) F(x) #31-34, 39

7-4: Work & Energy Loss of potential energy→work done→increase in Kinetic energy -  U → W → +  K Ex: falling mass in last week’s experiment Ch.7 (p.173) # 41, 46, 49, 52, (p.175) #65,

Ch.8: Energy conservation Conservative force: Work done doesn’t depend on path taken (curl x F = 0) Net work done around a closed path = 0 potential energy U depends only on x, and F x = -dU/dx E tot = K + U = constant (conservation of mechanical energy) Gravity and F elec are conservative; Friction and F mag are not Ch.8 (p.200) #7,9, 10, 16, 17, (p.202) 32, 36(a), 41, 42-47, 73, 82, 89, 93

Gravitational potential energy and force Near earthfar from Earth Force F Potential energy U

Ch.8-8,9: Energy diagrams and Power Power = rate of change of Energy P = dE/dt Minimum energy = stable state (F=0) Ch.8 (Power, 203) #57, 59, 62, 65, 67, (Diag) 68-71, 94-97

Phys.B: Raff : Introduction to Quantum Mechanics – Blackbody radiation Blackbodies were carefully studied in labs in late 1800s Rayleigh-Jeans theory explained long-wavelength tail: ~ 1/T (Wien’s law) Ultraviolet catastrophe at short !

Planck’s quantization of photon energy Planck’s phenomenological relation fit, but why? Three weeks later, Planck’s revolutionary explanation Probs and 11.8: Long and short- limits of blackbody radiation.

Blackbody radiation: notation Q = energy (joules)energy density u = Q/volume Q = dQ/d (J/m)energy density /wavelength u(T, ) = Q /volume Power = dQ/dt (J/s)emissive power = dP/d / area Luminosity = Power/area Prob. 11.9: Find energy maximum where du/d = 0

Photons as particles: Photoelectric effect Photons can knock electrons out of metal, if they can overcome the binding energy to the metal, or work function W. E photon = KE electron + binding energy: h = KE max + W Brighter light yields more electrons. Shorter wavelength light yields more energetic electrons. Even “weak” light beam of single photons can release e.

Atomic models