Physics

# Key Equations

PhysicsKey Equations

### 7.1Kepler's Laws of Planetary Motion

 Kepler’s third law $T 1 2 T 2 2 = r 1 3 r 2 3 T 1 2 T 2 2 = r 1 3 r 2 3$ eccentricity $e= f a e= f a$ area of an ellipse $A=πab A=πab$ semi-major axis of an ellipse $a= ( r a + r p )/2 a= ( r a + r p )/2$ semi-minor axis of an ellipse $b= r a r p b= r a r p$

### 7.2Newton's Law of Universal Gravitation and Einstein's Theory of General Relativity

 Newton’s second law of motion $F=ma=mg F=ma=mg$ Newton’s universal law of gravitation $F=G mM r 2 F=G mM r 2$ acceleration due to gravity $g=G M r 2 g=G M r 2$ constant for satellites orbiting the same massive object $r 3 T 2 = GM 4 π 2 r 3 T 2 = GM 4 π 2$
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