Tides3.5 - Understand the relative effects of the Sun and Moon in producing high and low, spring and neap tides
4.9 - Understand the lunar phase cycle
The gravitational attraction of the Moon and Sun on pulls Earth. The water on Earth's surface is pulled and the water causes tides.
Imagine if you were sat on a beach. You may notice the sea is a long way from the beach. This is low tide. Six hours later, you will find water surrounding you and lashing at your feet. This is high tide.
If the Moon had seas and oceans the tides would be even more dramatic than on earth because the pull of Earth would be much greater.
The Moon pulls water on Earth's surface nearest it and there is a force equal to this on the other side of the Earth.
Tides change at every position on Earth daily for 2 reasons -
1. The Moon orbits Earth
2. Earth rotates and water at the side (and opposite) facing the Moon is attracted to and from it.
There is another variable in all of this - The Sun.
The Sun exerts a tidal force approximately 40% that of the Moon.
When the Sun, Moon and Earth are in line (typically during a New and Full Moon) there are more dramatic tides. High tides are higher and low tides are lower.
These tides are called spring tides (From the Anglo Saxon word meaning 'leap'. They are not connected to the spring season.
When the Sun, Moon and Earth are not in line - when the Moon is at right angles (or quadrature) to Earth then the tides are less dramatic. High tides are lower than at other times. Low Tides are higher than at other times. These tides are called neap (From the Anglo Saxon word meaning 'scanty')
The tides have an effect on Earth's rate of rotation as they act as a brake slowing it down slightly.
Tides are not the same over the world as a lot depends on the depth of sea, channels, shape of land masses and continents etc.
There is a high and low tide twice a day. These are spread about 6 hours each apart.
The Severn Channel has the 2nd largest tidal difference in the world. The Bay of Fundy in Canada has the largest.