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The Big Idea
Over 2500 years ago Aristotle proposed two laws of physics governing motion. One for ‘Earthly bodies’ (objects on Earth) that states objects naturally go in straight lines and one for ‘Heavenly bodies’ (objects in space) that states objects naturally go in circles. This idea held steady for 2,000 years, until Isaac Newton in a triumph of brilliance declared that there is one law of physics that governs motion and he unified “earthly” bodies and “heavenly” bodies with the The Universal Law of
Gravitation. Newton used the universal law of gravity to prove that the moon is accelerating towards
Earth just as a body on Earth is falling towards Earth. The acceleration of both the moon and the object on Earth is calculated using the same formula. This theory is so well regarded that it has been used to hypothesize the existence of black holes and dark matter, later verified by observation. The search to unify the laws of physics into one theory continues today and is often referred to as the yet undiscovered Grand Unified Theory (GUT).
Key Equation: The Universal Law of Gravity
FG = Gm1m2 / r 2
; the force of gravity between an object with mass m1 and another object of mass m2 and a distance between them of r.
G = 6.67 x 10-11 Nm2/kg2 ; the universal constant of gravity
g = Gm / r 2
People’s Physics Book
; gravitational field strength or gravitational acceleration of a planet with mass m and radius r. Note that this is not really a separate equation but comes from Newton’s second law and the law of universal gravitation.
Ch 12- 1
Key Concepts
•
•
•
•
•
When using the Universal Law of Gravity formula and the constant G above, make sure to use units of meters and kilograms.
Newton invented calculus in order to prove that for a spherical object (like Earth) one can assume all of its mass is at the center of the sphere (thus in his formula, one can use the radius of Earth for the distance between a falling rock
Over 2500 years ago Aristotle proposed two laws of physics governing motion. One for ‘Earthly bodies’ (objects on Earth) that states objects naturally go in straight lines and one for ‘Heavenly bodies’ (objects in space) that states objects naturally go in circles. This idea held steady for 2,000 years, until Isaac Newton in a triumph of brilliance declared that there is one law of physics that governs motion and he unified “earthly” bodies and “heavenly” bodies with the The Universal Law of
Gravitation. Newton used the universal law of gravity to prove that the moon is accelerating towards
Earth just as a body on Earth is falling towards Earth. The acceleration of both the moon and the object on Earth is calculated using the same formula. This theory is so well regarded that it has been used to hypothesize the existence of black holes and dark matter, later verified by observation. The search to unify the laws of physics into one theory continues today and is often referred to as the yet undiscovered Grand Unified Theory (GUT).
Key Equation: The Universal Law of Gravity
FG = Gm1m2 / r 2
; the force of gravity between an object with mass m1 and another object of mass m2 and a distance between them of r.
G = 6.67 x 10-11 Nm2/kg2 ; the universal constant of gravity
g = Gm / r 2
People’s Physics Book
; gravitational field strength or gravitational acceleration of a planet with mass m and radius r. Note that this is not really a separate equation but comes from Newton’s second law and the law of universal gravitation.
Ch 12- 1
Key Concepts
•
•
•
•
•
When using the Universal Law of Gravity formula and the constant G above, make sure to use units of meters and kilograms.
Newton invented calculus in order to prove that for a spherical object (like Earth) one can assume all of its mass is at the center of the sphere (thus in his formula, one can use the radius of Earth for the distance between a falling rock