Gravity and our solar system

What is gravity?

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Gravity- force of attraction
between objects that is due to
their masses and the distances
between them.

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Greater mass= greater attraction

Why is it important?

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Gravity keeps the planets in orbit

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Orbit- path a body follows as it
travels around another body in
space.

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Inertia- tendency of an object to
move in a straight

KEPLER’S Law

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Planets follow elliptical orbits

◼ Aphelion- object is farthest away

from the sun

▫Speed of orbit is slower
▫We are in aphelion during our summer

◼ Perihelion- object is closest to the

sun

▫Planet is moving faster
▫We are in perihelion during our winter

Kepler and Newton

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What Newton said

◼ Force of Gravity between two objects increases as the

mass increases
▫ Something with a larger mass will have a greater pull

◼ Force of Gravity decreases as the distance between

the objects increase (or it increases as the distance
between the objects decrease)

Revolutions vs. Rotations

Revolution

Rotation

▶ The Earth revolves around

the Sun!

▶ Takes 1 year (365.25 days)

◦ Hence Leap Year

▶ Earth rotates on its axis

▶ Causes the seasons

▶ Takes 1 day (24 hours)

▶ Gravity keeps the planets in orbit

▶ Orbit- path a body follows as it travels

around another body in space.

▶ Inertia- tendency of an object to move

in a straight path

Why is it important?

▶ Tides are periodic rising and falling of large bodies of

water.

▶ They are caused by the gravitational pull of the Moon

and Sun. The gravitational attraction of the moon
causes the oceans to bulge out in the direction of the
moon.

▶ Another bulge occurs on the opposite side, since the

Earth is also being pulled toward the moon (and away
from the water on the far side). Since the earth is
rotating while this is happening, two tides occur each
day.

Tides:
How do they relate to gravity?

▶ Very High Tides

▶ Nothing to do with Spring

▶ Occur with the sun, moon,

and earth are in a line

▶ Occur during a new moon

(we see no moon) and a full
moon

Types of tides

Spring Tide

▶ Low tides are higher and

High tides are lower

▶ Occur with the sun and

moon are at a right angle

▶ Occur during the quarter

moons (when we see half
of the moon)

Types of tides

Neap Tide