Gravity Terms Gravity Orbits Inertia Ellipse How do

Gravity Terms • Gravity • Orbits Inertia Ellipse

How do the planets remain in their orbits ? • What two factors keep the planets in their orbits? • What is gravity? • What is inertia? • What two factors does the strength of the pull of gravity depend upon?

Gravity • All objects, from the atom to the largest family of stars, possess gravity. • Gravity is a force that attracts all objects towards each other. • The strength of the pull of gravity between two objects depends on two factors. • These two factors are the product of the masses of the objects and the distance between them.

Gravity • As the product of the masses increases, the pull of gravity also increases. • If the distance between the two objects increases, then the pull of gravity between them decreases. • All objects in our solar system travel around the sun in paths called orbits. • Planets orbit around the sun, and moons are in orbit around planets.

Gravity • Scientist Sir Isaac Newton discovered 3 Laws of Motion. • His 1 st Law of Motion states that an object in motion will tend to stay in motion at the same speed and direction unless acted on by an outside force. • The tendency of objects to keep doing what they were doing is called inertia.

Gravity • Inertia tends to lead planets to follow a straight path at a certain speed unless acted on by an outside force. This outside force is the gravity of the sun. • While the gravity of the sun pulls the planet towards it, the speed and direction (inertia) of the planet pushes it forward. • When the forces of gravity and inertia are balanced, the planet follows a curved path around the sun.

Quick Check • What force keeps Earth in orbit around the sun? • A. a pull by one object that is in contact with another object. • B. a push by one object that is in contact with another object. • C. mass • D. gravity

Quick Check • What affects the force of gravity between two objects? • A. the product of their masses and the distance between them • B. only the distance between them • C. only the sum of their masses • D. the mass of the larger object

Quick Check • In what direction does an object in space tend to move? • • A. in a curved path B. inward C. in a straight line D. backward

Quick Check • How would the force of gravity between Earth and the sun be affected if the mass of Earth were greater than it is? • A. The force of gravity would be unchanged. • B. The force of gravity would be greater. • C. The force of gravity would be less. • D. There would be no force of gravity.

Quick Check • If the force of gravity between Earth and the sun were greater than Earth’s inertia, what would happen to Earth? • A. Earth would escape into space. • B. Earth would fall into the sun. • C. Earth would remain in its orbit around the sun. • D. Earth would stop moving.