Gravity Continued and Waves

Chapters 9, 11.1, and 11.2

Reminders

• No lab this week.• In-class Quiz #4 will take place on Thursday,

October 23, focusing on Chapters 8 and 9.• No reading quiz prior to class on Thursday as

today’s quiz covered all of Chapter 11.

Gravity - Review

Orbital Velocity

In orbital motion, Fg = Fc, hence

Escape Velocity

Examples

• Force between two objects:

• Orbital velocity:

• Escape velocity:

– G = 6.67x10-11Nm2/kg2

– M = 5.97x1024kg– r = 6,371,000m

Sample Problems 1

• What is the gravitational force between a proton and an electron in a Hydrogen atom? – mp = 1.673x10–27kg

– me = 9.109x10–31kg

– ro = 5.29x10–11m– G = 6.67x10–11Nm2/kg2

• F = Gmemp/ro2

Sample Problems 2

• How much does a 53-kg astronaut weigh on the surface of Earth? Wt = mg

• How much does a 53-kg astronaut weigh 400km up in Earth orbit? Fg = -Fc

• How much would a 53-kg astronaut weigh standing on top of a 400km-hightower? F = Gmame/r2

Sample Problems 3

• What is the orbital velocity of the International Space Station (ISS) whose altitude is 330km? Take the radius of Earth to be 6378.1km. The mass of Earth is 5.97x1024kg

• What is the ISS’s orbital period? Recall that Δx = vt which implies 2πr = vP

• How does Earth’s escape velocity at the altitude of ISS’s orbit compare with the ISS’s orbital velocity?

Key Concepts Chapter 11, Sec 1-2

• Simple Harmonic Oscillator (a pendulum)• Terms: frequency (f), period (T), wavelength

(λ), amplitude (A); note f = 1/T• Wave forms:– Longitudinal– Transverse

• Polarization• Δx = vt implies v = λf