May the Force Be With You

 Every object in the universe has a mass that exerts a pull (force) on every other mass.  The size of the pull (force) depends on the mass of the object and the distance between objects.

 Example: gravitational pull of the Earth (large mass, strong pull) on molecules of atmospheric gases (small mass, weak pull) keeps the atmosphere close to Earth.  Example: You don’t get pulled from your seat into the sun because the Sun is too far away for its gravitational force to be strong.

Everything. You exert a gravitational force on your chair, the floor, even your classmates sitting beside you. The force you exert isn’t very strong because people aren’t as massive as Earth.

Examples: Mass of Earth = about 6.0 X kg Mass of fully loaded plane = about 7.0 X 10 4 kg Average mass of human = 68.5 kg

 Isaac Newton was a 17th century English physicist who developed three laws of motion and the law of universal gravitation.  These laws explain motions we observe on Earth and motions of planets, stars, galaxies and other celestial bodies.

 Myth: An apple fell on his head causing him to define gravity.  Fact: He watched an apple fall and wondered if all things were governed by this action. He asked questions, experimented and used math to find the answers.

Newton’s law of universal gravitation, states that the gravitational force between two objects is proportional to the mass of each, and inversely proportional to the distance between them.

It is written like this (G is the gravitational constant): F = Gm 1 m 2 /r 2 You will not have to know this equation!

large mass larger mass Close Stronger attraction large mass small mass Far apart Weaker attraction

The attractive force of gravity acts between the center of two objects.

 In the case of the superheroes standing on the Earth's surface, the effect of gravity attracts them towards the center of the Earth.  No matter where they stand on the earth, they don't fall off.

 The Sun’s gravitational pull keeps the Earth orbiting the Sun.  The Moon’s gravitational pull on the Earth creates a swell in sea level causing tides.

 A gravitational attraction between the Earth and the Sun can increase the effect of the Moon on tides; specifically the spring and neap tides.

 Planets are larger than their moons and keep the moons from falling away from the planet.  The moons would travel in a straight line without a force acting on it.

 Because of the force of the attraction of the planet to the moon, the moon’s straight-line fall is pulled into a curve.  The moon revolves around the planet because of the continuous pull of gravity.

 The Solar System is shaped much like an old fashioned phonograph record; most objects of the Solar System stay within the area of a large circular slice of space.

 The Sun, most of the planets, their moons (except for the dwarf planet Pluto and the comets) keeps within this relatively narrow band of space.

 The Sun, Moon and the planets all travel close to the ecliptic: an imaginary line in the sky that runs along the constellations of the Zodiac.

 As the planets travel along the ecliptic they can occasionally form a straight line across the sky which would rarely happen if they were traveling randomly across the entire sky.  A popular myth is that some terrible disaster will occur when this alignment occurs.

 On May 5, 2000 the planets Mercury, Venus, Earth, Mars, Jupiter, and Saturn were positioned in a line with the Sun. Also, the Moon was almost lined up between the Earth and Sun.  There were many predictions of global catastrophes such as melting ice caps, earthquakes, etc.  Nothing happened.

 The distance to the planets is too great for their gravity, magnetic fields, radiation, etc. to have any discernible effect on Earth.  The inner six planets are aligned every fifty to a hundred years or so.

 While unusual, such alignments have happened in the past without any consequences.  The planets are simply too far away to have an affect on anything here on Earth.