When you launch your model sailing boat, you can get an idea of how it is propelled by the wind. To sail in the direction they want to go, sailors must be aware of wind direction, so that they can adjust the position of the sails to make best use of it. If sailing boats face straight into the wind, the sails flap uselessly, and the boat is in a "no-go zone." They can, however, sail into oncoming wind by taking a zigzag course. This is called tacking. The wind blows against one side of the sail to propel the boat diagonally upwind. When the boat changes tack, the wind blows against the other side of the sail, and the boat goes forward on the opposite diagonal. If the wind is blowing from behind the boat, the sail is set at right angles to the boat like an open wing, so that it is filled by the wind.
Pencil, ruler, thick card, scissors, tape, plastic sheet, stapler, bradawl, nonhardening modeling material, thin garden canes, colored paper, plastic straw, small plastic bottle, string, paper clip, sheet of paper.