• Matter exerts a gravitational pull on other matter.
• The sun and the moon exert a gravitational pull on the earth.
• Liquid water shows the effects of this gravitational pull more than the solid earth.
• The ocean surface rises and falls because of the gravitational pull.
• These daily changes in water level are called tides.
• High tide – the highest level that ocean water reaches on shore.
• Low tide – the lowest level that ocean water reaches on shore.

Tide Patterns – repeat every 24 hours and 50 minutes.

1. Semidiurnal tides – two high tides, two low tides
2. Diurnal tides – one high tide, one low tide
3. Mixed tides – have a mix of diurnal and semidiurnal patterns

Spring tides – occur twice each month. Spring tides have the greatest difference between high and low tides.

Neap tides – have the least difference between high and low tides.