instruction: What is a surf board used for?
response: A surfboard is shaped like a narrow plank.  Surfers stand on the top of the surfboard and use it to surf on the ocean.  They tend to be light and are strong enough to get hit by a large wave without breaking in half.  Surfboards were originally invented in Hawaii and were made using the wood from local trees.  Early surfboards from Hawaii were over 15 feet long and were referred to as longboards.  Surfboards got a lot shorter as surfers had wanted to be more agile with them in the ocean.