Chapter 6 Lesson 3: Gravity and Orbit

What is gravity? Gravity is the force of attraction, or pull between any two objects Each planet is drawn toward the sun by gravity Gravity is affected by the total mass, and distance between the two objects An object’s mass always stays the same Your weight depends on mass, as well the force of gravity wherever you are located

Weight and Gravity Mass on Earth = 100 Weight on Earth = 100lbs Earth’s gravity =1 Mass on Jupiter = 100 Weight on Jupiter = 236lbs Jupiter’s gravity = 2.36 Mass on Moon = 100 Weight on Moon = 16.5lbs Moon’s gravity = .165

What keeps objects in orbit? An orbit is a path an object takes around another Planets orbit the sun Moons orbit their planets

Inertia Inertia is the tendency of a moving object to keep moving in a straight line. All objects have the property of inertia. Inertia alone would cause Earth to move in a straight line. Gravity and inertia together make Earth follow its path of orbiting the sun. The effect of gravity and inertia make the planets move in a circular orbit called an ellipse.

What causes the tides? Both the pull of gravity from the moon and sun affect Earth Moon is closer to Earth than the sun Sun’s pull of gravity is less than the moon’s pull of gravity Tide is the rise and fall of the ocean’s surface Most oceans have two high tides and two low tides

As the moon orbits around the earth, its gravity pulls water on the side nearest to it away from the land. This causes low tide About twice a month, the sun and the moon line up and both pull in the same direction. This causes higher tides and lower tides called “spring tides” Neap tides are tides with the smallest range which occur between spring tides, caused when the sun and moon pull in different directions

Review Questions Jupiter is about 320 times larger than Earth, but its gravity is only 2.36 times larger than Earth’s gravity. What might cause this difference? Suppose you have a dog that weighs 50lbs. How much would it weigh on a planet that had 3.45 times Earth’s gravity? Why dies food float in the space vehicle of the astronauts don’t hold onto it? Why do stronger tides occur when the sun and moon are lined up? Why do spring and neap tides occur twice a month? How is the gravity between two objects affected by their masses? The rise and fall of the ocean’s surface is the _____________. How are mass and weight different? What force keeps earth in its orbit around the sun? What tide occurs twice a month when the sun and moon pull in different directions?