Grades 3–5 · Machines
How can a sailboat travel toward the wind?
A sailboat can reach a place that lies toward the wind, but it cannot sail straight into the wind using ordinary sails. Instead, it follows a slanting course on one side of the wind, then turns to follow a slanting course on the other side. This zigzag travel is called tacking.
In the diagramA sailboat travels toward the wind in slanting legsWind comes downTacking routeForces on one slanting legKeelAirWaterForwardKeel limits sideways drift.Arrows show directions; real forces and boat speed vary.
On a useful slanting course, air flows around the sail and changes direction. The air pushes on the sail. Part of this push acts forward along the boat, and part acts sideways. Beneath the boat, a fin called a keel moves through the water. The water pushes against it and limits sideways drift. A smaller boat may use a board with a similar job.
The sail and keel work with two different surroundings: air and water. Together their forces allow forward movement, while water resistance also holds the boat back. Each slanting leg can take the boat closer to its upwind destination. Pointing directly into the wind removes this useful arrangement, and the sails may flap instead of driving the boat forward.
About this explanation
Starting knowledge: Recognize wind as moving air and a push as having a direction.
Sources
- University of New South Wales, School of Physics — The physics of sailing