Motions of the Earth

….it’s what moves us

Two motions of the Earth

Rotation- Circular movement of an object around an axisRevolution-The movement of an orbiting object completely

around another object

Rotation of Earth

• 1 complete rotation = 24 hours = 1 Day• Angular velocity at equator = 1000 mph• Earth rotates around an axis (23 ½ degrees)• Earth’s rotation is slowing by 2.2 seconds

every 100,000 years

Earth’s Revolution

• 1 complete orbit around sun = 365 ¼ days• Travels 940 million km in 1 year.• Average speed of 67,000 mph

What is an orbit?

• An orbit is a regular, repeating path that an object in space takes around another one.

• An object in an orbit is called a satellite. A satellite can be natural, like the moon, or human-made.

Orbit picture

Orbits continued…..

• In our solar system, the Earth orbits the Sun, as do the other seven planets.

• All travel on or near the orbital plane, an imaginary disk-shaped surface in space.

• All orbits are circular or elliptical in shape. • In addition to the planets' orbits, many planets

have satellites which orbit around them.

Ellipses vary in shape from very broad and flat to almost circular.

Circle vs. Ellipse

Circle- A circle is a closed curved shape that is flat.- All points on the circle are equal distance from

the center

Ellipse- A closed curved shape that is flat. - Any two distances from two points inside the

ellipse always add up to same number.

Orbits are Ellipses

• Though most orbits are very nearly circular, they are all elliptical, or circles that are slightly flattened.

What causes orbits to happen?

• Orbits are a perfect balance between the forward motion of a body in space and the pull of gravity on it from another body in space

What causes orbits?

• Continuous tug-o-war between moving object and the pull of gravity from another object

Forces of orbit

Inertia and Gravity

• Inertia and gravity have to be perfectly balanced for an orbit to happen.

• If the forward movement (inertia) of one object is too strong, the object will speed past the other one and not enter orbit.

• If inertia or momentum is much weaker than the pull of gravity, the object will be pulled into the other one completely and crash.

Inertia and Gravity Pics

Gravity

• Force pulling together all matter

• The more matter, the greater the gravity.

• Mass is how we measure amount of matter

How does my gravity measure up?

• As we walk on the surface of the Earth, it pulls on us, and we pull back. The Earth is much more massive than we are, so the pull from us is not strong enough to move the Earth, but the pull from the Earth can make us fall flat on our faces.

Force of gravity depends on…

Mass- The more massive an object, the greater the

gravity

Distance- The closer an object

is, the greater the gravity.

*This is why we are stuck on Earth and not pulled away to the sun even though the sun is much more massive than the earth

Movement in Space

• Objects in space follow the laws of physics, just like objects on Earth do.

• Things in space have inertia. That is, they travel in a straight line unless acted on by an outside force

• The movement of things in space is influenced by gravity.

• Gravity can change the course of bodies in space or pull them off course, or cause them to crash together.

How does Gravity work in Space?

• Every object in space exerts a gravitational pull on every other.

• It is the glue that holds together entire galaxies, keeps planets in orbit, makes it possible to use human-made satellites and to go to and return from the Moon.

• It makes planets habitable by trapping gasses and liquids in an atmosphere.

• It can also cause life-destroying asteroids to crash into planets.

Object Distance from the Sun

Distance traveled in one year

Amount of time for one complete orbit of the Sun (one "year.")

Mecury 36,800,000 miles 57,900,000 miles 3 Earth months

Venus 65,100,000 miles 108,200,000 miles 7 Earth months

Earth 93,000,000 miles 149,600,000 miles 1 Earth year (365.25 days)

Mars 139,500,000 miles 227,900,000 miles 23 Earth months. Almost 2 Earth years.

Jupiter 483,600,000 miles 778,300,000 miles 142 Earth months. Almost 12 Earth years.

Saturn 883,500,000 miles 1,427,000,000 miles 354 Earth months. (29.5 Earth years)

Uranus 1,785,600,000 miles 2,869,600,000 miles 1008 Earth months. (84 Earth years)

Neptune 2,790,000,000 miles 4,496,600,000 miles 1978 Earth months (almost 165 Earth years)

Pluto 3,627,000,000 miles 4,913,500,000 miles 2976 Earth months (248 Earth years)