Newton's Third Law describes lift in terms of the reaction of the wind's air particles to the mainsail and jib. The law states that every action has an equal and opposite reaction. As the wind hits the sails from an opposing direction (remember, you're sailing upwind to tack), it generates drag, or backward pull. Drag is parallel to the original wind current  and occurs naturally when something is moving against a fluid or gas. Swimmers wear specialized suits and caps to reduce drag as much as possible in the water.

Examining lift through the Newtonian lens, the air particles' movement creates an equal, opposite reaction -- or forward pull. It can also be applied to the interaction of the sails and the keel, described in the previous section. The sails and the keel create equal and opposite reactions to focus the boat's energy forward rather than sideways.