水手英语 水手英语 How do Tides Work.pptx

How do Tides Work?What are Tides?Tides are the daily rise and fall of Earth’s waters on its coastlines. As the tide comes in, the level of water on the beach rises, and as the tide goes out, the level of water on the beach goes down. What Causes Tides?Tides are caused by the interaction of the Earth, the Moon, and the Sun. Gravity is the reason for tides. Moon’s Gravity – Tidal BulgesThe Moon pulls on the water on the side nearest to it more strongly than it pulls on the center of the Earth. This pull creates a bulge of water, called a tidal bulge on the side of Earth facing the the Moon. The water on the side of Earth facing away from the Moon has a less strong pull. This water is “left behind” and forms a second bulge. Tidal Bulges – High TideIn places where there are tidal bulges, high tide is occurring along the coastlines. High TideHigh TideHigh TidesHigh tides are when the water reaches its highest point. Tidal Bulges – Low TideIn places between the bulges, low tide is occurring. Low Tide Low Tide Low TidesLow tides are when the water reaches its lowest point. Sun’s Gravity and TidesThe Sun is so large that its gravity also affects tides. At times, the Sun and Moon pull together on Earth’s waters in the same direction. At other times they pull in different directions.Spring TidesSpring tides occur two times a month, during a full and new moon when the Earth, Sun, and Moon are lined up. Spring tides have the highest high tides and lowest low tides. Neap Tides Neap tides occur at the first and third quarters of the Moon when the Sun and Moon pull at right angles to each other. Neap tides have the lowest high tides and highest low tides . 主讲人：薛俊洁