The Earth in Space The Earths Gravity Gravity

The Earth in Space

The Earth’s Gravity ► Gravity – force of attraction between all matter. ► Law of Gravitation – the force between two objects depends upon their masses and the distance between them Isaac Newton

► Are weight and mass the same? § No! ► Mass = the amount of matter in an object ► Weight = strength of the pull of gravity ► Weight is measured in NEWTONS ► Weight depends on: § An object’s mass and § The object’s distance from the Earth’s center

►Knowing this, and that the Earth’s true shape is an oblate spheroid, where on Earth would you weigh the MOST…at the Poles or at the Equator?

. 3% more at the POLES

Movements of the Earth A. Rotation – the spinning of Earth on its axis § This takes 24 hours

B. Revolution ►Earth’s orbit around the sun. ►This takes 365. 25 days § Perihelion – Earth is the closest to the sun (January 3 rd) § Aphelion – Earth is the furthest AWAY from the sun (July 4 th)

►What causes Earth’s seasons?

The Seasons 1. Summer Solstice – first day of summer (in the Northern Hemisphere)! § June 21 st or 22 nd § Northern hemisphere is tilted TOWARDS the sun § Sun’s rays are directly over the Tropic of Cancer § 24 hours of sun at the Arctic Circle § 24 hours of darkness at the Antarctic Circle

2. Winter Solstice – first day of winter (in the Northern Hemisphere) § December 21 st or 22 nd § Northern Hemisphere is tilted AWAY from the sun § Sun’s rays are directly over Tropic of Capricorn

3. Autumnal Equinox § September 21 st or 22 nd § Sun is directly over the Equator § Equinox – EQUAL day and night everywhere

4. Vernal Equinox § March 21 st or 22 nd § Sun is directly over the Equator § Equinox – EQUAL day and night everywhere