Whenabigboat，likeacruiseship，goesthroughtheocean，itoftencreateswaves．Thishappenswhenthelargeenginesonthebackofthecruiseshipcausethewaterontheocean'ssurfacemoveupanddownviolently．Thesewavesmoveoutfrom

　　When a big boat，like a cruise ship，goes through the ocean，it often creates waves．This happens when the large engines on the back of the cruise ship cause the water on the ocean's surface move up and down violently．These waves move out from the boat in both directions．If you are captaining a smaller boat，you'd better steer clear of a ship's wake，so that your boat is not surfing on the waves，causing it to overturn

　　A wave is a pattern of motion．When you look at a wave，it may appear as simply water moving across the surface of the ocean．In fact，this is false．The water is actually not moving in the same direction as the wave．While the wave itself--the pattern of motion-is moving across the surface of the ocean，the water is actually moving in a circular motion，which brings the water molecules back to their original position．The water merely gives the appearance of moving forward．

　　If this is confusing，think of the kind of wave you do at a baseball stadium．Viewed from a distance，the wave is clearly moving across the stadium．But the thing that makes up the wave-the people-are not moving across the stadium，they're just moving up and down in their seats．This is just like the water in an ocean wave．A lot of water is moving up and down，which gives water the appearance of moving along with the wave．

　　Surfers pay a lot of attention to waves．If you're not in an area where the waves are suitable for surfing，then you can't surf．Usually，surfers gather in areas known for big waves-waves that rise high off the ocean's surface．If the wave is bigger，then the surfer is often able to surf for longer distances and perform more tricks．The height of a wave is known as its amplitude．If you could make a wave freeze，then you could measure the wave's amplitude by running a tape measure from the ocean's surface to the very peak of the wave．

　　All waves can be measured using amplitude and wavelength．While the waves created by a boat have very small amplitude-som