Mechanics Mania
Engineering Connection
Engineers of all disciplines use their knowledge of forces to design machines, structures and appliances. Aeronautical engineers build on their understanding of lift, weight, thrust and drag to design jets, helicopters, wind turbines, wind surfers and spacecraft — vehicles that move in air or space. Other engineers apply the same concepts to objects that travel on land and in water. Engineers design the shape of vehicles to be more aerodynamic to reduce drag force and thus reduce fuel consumption.
Introduction/Motivation
Have you ever wondered what makes things move? What makes a huge, heavy airplane fly in the air? Why do swings work when you pump your legs? Why do parachutes slow things down when they're falling? Why do trees sway in the wind? Why does wind happen, even?
The answer to all these questions is: forces. Engineers use physics to study forces, and then apply what they learn about forces to solve problems. Forces can make things speed up, and balanced forces can make things stay still or move at a constant speed.
In this lesson, we will learn about forces by examining airplanes and parachutes. We will learn that more than one force acts on things that fly, and we will see what we can do to change forces. In other words, we'll learn why airplanes can fly! Refer to the associated activities Heavy Helicopters and Blow-and-Go Parachute to help illustrate how these forces affect air craft flight!
After a winter of experimenting with an air tunnel (an enclosed space with a stationery object surrounded by moving air) to learn more about the forces of flight, Wilbur and Orville Wright flew the first airplane that could be controlled in the air in 1903. Today, more than 4,000 public airports in the U.S. provide convenient travel and exploration around the world. People ride in hot-air balloons and jump out of airplanes with parachutes for fun, trusting that a balance of forces will keep them from hitting the ground too hard. An understanding of forces allows aeronautical engineers to design all the different kinds of airplanes, hot-air balloons, and parachutes that have ever flown!
The SR-71 Blackbird was a high-altitude reconnaissance aircraft developed in the 1960s.
The Wright Brothers First Flight
Pay attention to the wing shape and the way the plane took off
SR-71 Blackbird
This thing is a BEAST!
Aerodynamics, the study of flight, is founded on four basic forces — lift, weight, thrust and drag. The interaction of these forces explains the movement of objects as they soar through the sky. What seems like magic — a several ton object flying, like an airplane flying through the sky! — is actually based on the laws of physics and these four forces.
The first force, lift, pushes up on things that fly — airplanes, birds, helicopters and rockets. The shape of the wings on an airplane and the whirling blades of a helicopter create lift as they move through the air.
The second force is weight — the force of two masses being attracted to each other. Weight is the force that pulls us towards the center of the earth, and why things fall down.
The third force is thrust. Thrust is created by the jet engines or propellers of an airplane. Birds create thrust (and lift!) with their wings. Thrust pushes things that are flying.
The fourth force is drag. Drag pushes against things moving through the air. It is caused by air particles bumping into the object. An object that is going faster bumps into more air particles, and so experiences more drag. Similarly, an object with a large surface area bumps into more particles, and experiences more drag.
When the forces are not balanced, flying objects speed up, slow down or change direction. This is called acceleration. For example, when the thrust force is bigger than the drag force, an airplane speeds up. When the lift force is bigger than the weight force, the airplane goes up faster.
When forces are balanced, objects do not accelerate. An airplane that is flying in a straight line at a certain speed has balanced forces. An airplane can even be going up or down and have balanced forces. As long as the airplane is not turning, speeding up or slowing down (in any direction, even up and down!) the forces are balanced.
Sometimes, two of the forces may be the same thing. For example, a rocket engine pushes a rocket straight up, providing both lift and thrust. A parachute could be caught in an updraft, and then the drag force could also provide lift. Not all four forces need to be present, either — if there is no wind, a hot air balloon would not have any thrust acting upon it, only lift, drag and weight. This may seem confusing, but that's okay. The important thing to remember is that the interaction of forces (whatever they're called) is responsible for everything that speeds up, slows down, stays still or moves at a constant speed.