Gravity is the force that governs motion in the solar system.
Newton's law of universal gravitation states every object in the universe attracts every other object.
The force of gravity is measured in units called newtons.
Factors Influencing Gravity
Mass: Objects with more mass have more gravity.
Weight: Weight is the force of gravity pulling on an object.
Weight changes based on location, while mass remains constant.
Weight = mass * gravity
Distance: As distance increases, gravitational force decreases
Inertia
Inertia is the tendency of an object to resist a change in motion.
Newton's first law of motion (law of inertia): An object at rest stays at rest, and an object in motion stays in motion with constant speed and direction unless acted upon by a force.
Orbital Motion
Gravity and inertia keep the moon in orbit around the Earth.
Without Earth's gravity, the moon would move in a straight line.
The sun's gravity keeps Earth in orbit, and Earth's inertia prevents it from crashing into the sun.