 # AIM How does gravity affect the movement of

• Slides: 13 AIM: How does gravity affect the movement of planets? Gravity • Gravity: the force of attraction between objects that can act across great distances. • The Sun’s gravity keeps the planets in their orbits around it. • The Earth’s gravity keeps the Moon in its orbit. • The gravitational attraction between two objects depends on two things: 1. Distance between objects 2. Mass of the objects Why don’t planets just fall into the Sun? • British mathematician, Isaac Newton, explained how gravitational forces and inertia interact to produce orbital motion. 1. Universal Law of Gravitation: • As the mass of objects increases, gravitational attraction INCREASES. • As the distance between two objects increases, gravitational attraction DECREASES. 2. Newton’s first law of motion: An object at rest will stay at rest, and an object in motion will stay in motion, unless something acts on it to change that motion. – Inertia: the tendency of an object to remain in motion along the same, straight path. Animation As mass of two objects increases, the gravitational force between them ____. As the distance between two objects increases, the gravitational force between them _____. How does gravity cause tides? • Tides: the cyclic rise and fall of ocean waters. Local Tides for Kings Point, NY   Why does Earth have Tides? • Tides are a result of the gravitational attraction between the Earth, the Moon, and the Sun. • The Moon has the greatest effect because it is about 400 times closer to us than the Sun. • As Earth rotates, the low and high tides follow the alignment of Earth and the moon. • The time between two high (or two low) tides is ideally about 12 hours and 25 minutes.