1. GRAVITY & Tides

2. Just to Review…
As we talked in the previous class, gravity (gravitational force) is an attractive force between two objects. It is affected by:
Mass of the objects
Distance between the objects
Gravity pulls in all directions. But, the pull from the Earth’s gravitational force is stronger than any other object on the planet. This is why we see gravity pull objects down to the Earth.

3. Not Just the Earth…
Other objects in the universe also have their own gravity.
Moon
Sun
Their gravitational force has an impact on the Earth.

4. Everything Revolves Around…
Let’s start with the Sun. The Sun is at the center of our Solar System.
Everything revolves around it.
This is due to the large gravitational force of the star.
This model was first proposed by Copernicus in the 16th century. It went against the current beliefs that the Earth was at the middle of the Universe.
Two more scientists, Galileo and Kepler, would come later to support his theory, using Newton’s Law of Universal Gravitation to explain why planets orbit the Sun.

5. Everything Revolves Around…
The Earth is held in an orbital motion around the Sun by the Sun’s intense gravitational pull.
Like swinging a ball on the end of a string.
There is a gravitational force between the Moon and the Earth as well. This causes the Moon to orbit the Earth like a satellite, similar to the relationship between the Earth and the Sun.

6. Rise and Fall of the Tides
However, there is another effect from the gravitational force between the Moon.
The pull of the gravitational force from the Moon, combined with the force from the Sun is what creates tides here on Earth.
There are two types of tides:
Spring tide
Neap tide

7. Rise and Fall of the Tides
In a Spring tide, the Moon and the Sun work together, creating larger waves.
There is more force pulling on the water since they are working together.
These occur when there is a straight line formed between the Moon and the Sun
happens 2 times per month, during full moon and new moon phase
During a Neap tide, the Sun partially works against the Moon, creating lower waves.
There is less force pulling on the water.
These occur when the Moon is at a right angle (90°) to the Sun.
happens 2 times per month, during first quarter and last quarter moon