Gravity 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. What is Gravity?

❖ 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. What is Gravity?

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

Examples: Mass of Earth = about 6.0 X kg (move the decimal 24 spaces to the right) 6,000,000,000,000,000,000,000,000 kg Mass of fully loaded plane = about 7.0 X 10 4 kg Average mass of human = 68.5 kg What Does Gravity Attract?

❖ 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. Law of Universal Gravitation

❖ 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. Isaac Newton

❖ 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. Law of Universal Gravitation

Law of Universal Gravitation Illustrated Large Mass Larger Mass Close Stronger Attraction Large Mass Small Mass Far Apart Weaker Attraction

Why Don’t They Fall Off?

Gravity Pulls toward the Center The attractive force of gravity acts between the center of two objects.

❖ In the case of the figures 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. Gravity Pulls toward the Center

❖ 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. Effects of Sun & Moon

❖ A gravitational attraction between the Earth and Sun can increase the effect of the Moon on tides. Effects of Sun & Moon

❖ 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. Planets & Moons

❖ 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. Planets & Moons

❖ Because of the Earth’s gravity, satellites, the space shuttle (previously), and the International Space Station (ISS) orbit the Earth. ❖ Astronauts appear to be weightless because the Earth’s gravity is constantly pulling the vehicle out from under their feet. The vehicle has a much larger mass than their bodies. Earth and Objects in Space

❖ The solar system is shaped much like an old record; most objects of the solar system stay within the area of a large circular slice of space. Sun & Solar System Objects

❖ The Sun and most of the planets and their moons (except for the dwarf planet Pluto and the comets) keep within this relatively narrow band of space. Sun & Solar System Objects

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

❖ 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. Sun & Solar System Objects

❖ 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. Planetary Alignment

❖ The distance to the planets is too great for their gravity, magnetic fields, radiation, etc. to have any noticeable effect on Earth. ❖ The inner six planets align every fifty to a hundred years or so. Planetary Alignment

❖ 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. Planetary Alignment

❖ What is gravity? ❖ How does gravity affect objects? ❖ How do the objects in our solar system stay in their respective orbits? Reflection Questions

On a loose sheet of paper, 3- List 3 ways that gravity affects objects in our universe 2 - List 2 factors that affect the magnitude (amount) of the force of gravity acting on an object. 3 - List 1 way that our universe would be different without gravity