Planetary Motion and Gravitation PDF

Lesson 1 Planetary Motion and Gravitation  Focus Question What role does gravity play in planetary motion?  New Vocabulary Kepler’s first law Kepler’s second law Kepler’s third law gravitational force law of universal gravitation  Review Vocabulary Newton’s third law: sta...

Lesson 1 Planetary Motion and Gravitation  Focus Question What role does gravity play in planetary motion?  New Vocabulary Kepler’s first law Kepler’s second law Kepler’s third law gravitational force law of universal gravitation  Review Vocabulary Newton’s third law: states that all forces come in pairs and that the two forces in a pair act on different objects, are equal in strength, and are opposite in direction  Early Observations In ancient times, the Sun, the Moon, the planets, and the stars were assumed to revolve around Earth. Nicholas Copernicus proposed that Earth and other planetary objects revolved around the Sun. Tycho Brahe, using instruments that he designed and built, is credited with the most accurate measurements of his time.  Kepler’s Laws Kepler’s first law states that the paths of the planets are ellipses, with the Sun at one focus.  Kepler’s Laws Kepler’s second law states that an imaginary line from the Sun to a planet sweeps out equal areas in equal time intervals.  Kepler’s Laws Kepler’s third law states that the square of the ratio of the periods of any two planets revolving around the Sun is equal to the cube of the ratio of their average distances from the Sun. Thus, if the periods of the planets are TA and TB, and their average distances from the Sun are rA and rB, Kepler’s third law can be expressed as follows:  Newton’s Law of Universal Gravitation Beginning in 1666, Isaac Newton studied planetary motion and concluded that an attractive force must act between any two bodies with mass. The force of attraction between two objects, called the gravitational force, must be proportional to the  Newton’s Law of Universal Gravitation The law of universal gravitation states that objects attract other objects with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them. Law of Universal Gravitation:  Universal Gravitation and Kepler’s Third Law Newton’s law of universal gravitation can be combined with the definition of a period to find the period (T) of an object orbiting the Sun. Period of a Planet Orbiting the Sun Squaring both sides makes it apparent that this equation is Kepler’s third law of planetary motion: The square of the period is proportional to the cube of the  Measuring the Universal Gravitational Constant In 1798, English scientist Henry Cavendish used equipment similar to the equipment shown to measure the gravitational force between two objects. The experimental value of G is: G = 6.67 × 10−11  Quiz 1 According to Kepler’s first law, what do. the orbits of the planets look like? A circles C irregular zig-zags B regular zig-zags D ellipses CORREC T  Quiz 2 According to Kepler’s first law, what. is at the focus of a planet’s orbit? A planet C Sun CORREC T B star D Moon  Quiz 3 In the equation for Kepler’s third law, what. should be in place of the x? A 1 B 2 C 3 CORREC T D 4  Quiz 4 Which two factors is the gravitational. force between two objects dependent upon? A mass, distance CORREC T B weight, force C velocity, mass D acceleration, mass  Quiz 5 This law graph. applies to which law? A Kepler’s first law B Kepler’s second law C law of universal gravitation CORREC D Kepler’s thirdTlaw