Question

So how do sailboats sail up wind? It is obvious how they move with the wind but definitely not so obvious how they go against the wind. Going along with this, baseballs would still fly even if there was no lift but how do frisbees and boomerangs work?

Answer 1

Sailing into the wind is possible when the sail is angled in a slightly more forward direction than the sail force. In this aspect, the boat will move forward because the keel (centerline), of the boat acts to the water in as the sail acts to the wind. The heeling force of the sail is balanced by the force of the keel.

It seems intuitive that sailboats, powered only by the wind, can travel easily with the wind at their backs, but it may seem impossible that they turn around and come home again, with the wind blowing straight against them.

But this reverse movement is possible because a moving boat's sail is shaped as an airfoil like the wing of a plane. When air moves over a plane's wing, from front to back, wind flowing over the top of the wing has to travel farther than wind flowing under the wing's bottom surface. This creates a pressure difference that lifts the plane.

On a sailboat, wind blowing against the boat at an angle inflates the sail, and it forms a similar foil shape, creating a difference in pressure that pushes the sail perpendicular to the wind direction.

How Boomerangs Work

by Tom Harris

When most of us think of boomerangs, we imagine somebody (quite possibly a cartoon character) throwing a banana-shaped stick that eventually turns around and comes right back to the thrower's hand (possibly after hitting another cartoon character in the head). This idea is simply amazing, and as children, our first reaction to such a device was: This stick is obviously possessed with magical powers! Of course, the person or people who discovered the boomerang hadn't actually found a magical stick, but they had come upon an amazing application of some complex laws of physics. In this edition of HowStuffWorks, we'll break down the physical principles that make boomerangs work, see what happens as a boomerang flies through the air and find out the proper way to throw a boomerang so that it comes back to you. We'll also delve a little into the history of boomerangs to see how they came about in the first place. Boomeranging is an amazing demonstration of scientific principles as well as a terrific sport you can enjoy all by yourself. What is It? When we talk about boomerangs, we usually mean the curved devices that return to you when you throw them, but there are actually two different kinds of boomerangs. The kind we're all familiar with, returning boomerangs, are specially crafted, lightweight pieces of wood, plastic or other material. Traditionally, these are basically two wings connected together in one banana-shaped unit, but you can find a number of different boomerang designs available these days, some with three or more wings. Most returning boomerangs measure 1 to 2 feet (30 to 60 cm) across, but there are larger and smaller varieties. When thrown correctly, a returning boomerang flies through the air in a circular path and arrives back at its starting point. Returning boomerangs are not suited for hunting -- they are very hard to aim, and actually hitting a target would stop them from returning to the thrower, pretty much defeating the purpose of the design. Returning boomerangs evolved out of non-returning boomerangs. These are also curved pieces of wood, but they are usually heavier and longer, typically 3 feet (1 meter) or more across. Non-returning boomerangs do not have the light weight and special wing design that causes returning boomerangs to travel back to the thrower, but their curved shape does cause them to fly easily through the air. Non-returning boomerangs are effective hunting weapons because they are easy to aim and they travel a good distance at a high rate of speed. There is also such a thing as a battle boomerang, which is basically a non-returning boomerang used in hand-to-hand combat. Why Does It Fly? If you throw a straight piece of wood that's about the same size as a boomerang, it will simply keep going in one direction, turning end over end, until gravitypulls it to the ground. So the question is, why does changing the shape of that piece of wood make it stay in the air longer and travel back to you? The first thing that makes a boomerang different from a regular piece of wood is that it has at least two component parts, whereas a straight piece of wood is only one unit. This makes the boomerang spin about a central point, stabilizing its motion as it travels through the air. Non-returning boomerangs are better throwing weapons than straight sticks because of this stabilizing effect: They travel farther and you can aim them with much greater accuracy. The returning boomerang has specialized components that make it behave a little differently than an ordinary bent stick. A classic banana-shaped boomerang is simply two wings joined together in a single unit. This is the key to its odd flight path. The wings are set at a slight tilt and they have an airfoil design -- they are rounded on one side and flat on the other, just like an airplane wing. If you've read How Airplanes Work, then you know that this design gives a wing lift. The air particles move more quickly over the top of the wing than they do along the bottom of the wing, which creates a difference in air pressure. The wing has lift when it moves because there is greater pressure below it than above it. Unlike an airplane or helicopter propeller, which starts spinning while the vehicle is completely still, you throw the boomerang, so that in addition to its spinning propeller motion, it also has the motion of flying through the air.