PHYS1001 Lecture Notes - Lecture 4: Circular Motion, Mass, Equivalence Principle
Lecture 4- Newton's law of gravitation
• The center of mass is the point in an object which behaves like a particle with the mass
of the object
• The force is directly proportional to their mass and inversely proportional to the square
of their separation
◦ F= -Gm1m2
▪ r^2
◦ Newton’s gravitational constant- least accurate number in physics
▪ 6.67384(80) x 10^-11
• Gravity is the weakest of the fundamental forces (its just that planets and stars are
really big)
◦ On earth a 1kg mass gives:
◦ m1= 10^25kg m2= 1kg
◦ r- 1000km
◦ F- 10N
• Gravity is always attractive
• The equivalence principle- initial mass and gravitational mass are equivalent
◦ Implies all objects in a gravitational environment fall at the same rate- all
objects fall with the same acceleration
◦ a = g
◦ If the same property of matter (mass) measures both inertia and gravity
◦ center of mass determine show quickly it will fall
◦ g=.81ms^-2- near the earth’s surface
◦ Moon pulls tide by gravitational pull
Orbit
• Consist free fall
◦ Moon around earth, earth around sun
• Generally elliptical
• Uniform circular motion
• F= ma= -m
• a is called centripetal acceleration
Pendulums
• Oscillators
• If theta is small then the pendulum’s motion is harmonic (evolves as a sin/cosine), and
determined only by its length, and local gravity
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Document Summary
F= -gm1m2 r^2: gravity is the weakest of the fundamental forces (its just that planets and stars are. Newton"s gravitational constant- least accurate number in physics. On earth a 1kg mass gives: m1= 10^25kg m2= 1kg r- 1000km. F- 10n: gravity is always attractive, the equivalence principle- initial mass and gravitational mass are equivalent. Implies all objects in a gravitational environment fall at the same rate- all objects fall with the same acceleration a = g. If the same property of matter (mass) measures both inertia and gravity center of mass determine show quickly it will fall g=. 81ms^-2- near the earth"s surface. Orbit: consist free fall, generally elliptical, uniform circular motion, f= ma= -m, a is called centripetal acceleration. Pendulums: oscillators, if theta is small then the pendulum"s motion is harmonic (evolves as a sin/cosine), and.
