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Lesson: Get a Lift!

In this lesson, adapted from Smithsonian Education and TeachEngineering.com, you’ll introduce your students to the four forces of flight — drag, lift, thrust, and weight — through a variety of fun flight experiments. Students will “fly” for short periods and then evaluate factors that might either increase or decrease their “flight” duration. They also will discover how air moving at different speeds over a wing keeps planes aloft.

Learning Objectives

At completion of these activities, learners will:

1. Understand the principles of flight.

2. Create, observe, and describe situations where air moves across different surfaces

3. Use prior and newly acquired knowledge to draw conclusions about why planes fly.

Standards

Standard A: Science as inquiry.

Standard B: Physical science; forces and motion.

Standard E: Abilities of technological design.

Standard G: Science as a human endeavor.

Vocabulary:

Air Pressure: The force exerted by air on an area.

Bernoulli’s Principle: The law that pressure exerted by a fluid decreases as the rate of flow increases.

Drag: The resistance caused by the shape of an object and its movement through the air

Fluid: Any substance where the molecules move around freely. Fluids are gases or liquids.

Force:  A push or pull on an object. See NASA’s Forces on Aircraft.

Lift: The upward force created by a difference in air pressure above and below the wings that causes the aircraft to move upwards. Moving air creates this difference as it flows around a wing.

Thrust: The force developed by a propeller or jet engine that drives an airplane through the air. (In the jumping activity, studentss’ leg muscles provided thrust.)

Weight: A measure of the heaviness of an object.

BERNOULLI BRAIN TEASERS

To pilots, lift means the way that air holds up airplanes and other flying objects. These activities will show you how this force works–and they don’t require a pilot’s license.

Worksheet: Have the students record measurements and follow along with the activity on their worksheet. After students have finished their worksheet, have them compare answers with their peers. Discuss as a class.

Class Discussion: Have the students engage in open discussion to suggest solutions to the following problem:

  • Given what we have learned, how does the Bernoulli Principle relate to airplane flight? (Answer: If air moves faster on one side of an object, the air pressure decreases and the object will move in the direction of the faster moving air. This is how wings create lift and why the objects in this experiment move in the direction of the faster air.)

1) USE YOUR LIPS TO LEVITATE

Materials: Paper                   

Hold a piece of paper between your thumb and forefinger, as shown in the picture. Now blow over the paper. What happens?

2) BALLOONS THAT BOGGLE

Materials: Balloons, String, Water

Try this activity with a friend. Blow up two balloons and tie each one to a string. Hold the balloons a few inches apart and try to blow them together.
Can you do it? What happens?
Try different ways of blowing on the balloons to see what happens.
(Hint: Squirt a little water into the balloons before you blow them up. This will help steady them.)

3) HUFF, PUFF, AND BLOW DOWN A PAPER TENT

  1. Have the students fold a piece of paper (lengthwise) in half and make a paper tent.
  2. Ask the students to predict what will happen when they blow into the tent. Will it appear to get larger, will it remain unchanged, or will it bend down toward the table? (Alternately, have students turn their paper tents upside down and blow through the V shaped paper.)
  3. Make sure the students notice that the tent flattens. This is because the air moving through the inverted V has less pressure, so the higher pressure on the outside of the paper tent flattens the paper.
  4. Have the students experiment with their paper tents, answer the relevant worksheet questions, and discuss their results

What’s Going On — The Simple Explanation:

Air never pulls or sucks; it pushes. Air is pushing on you right now from every direction. We’re so used to air being around us that we often don’t notice it. This constant push of air is called air pressure.

Now think about what was happening in the activities you just finished. Why did the balloons come together when you blew between them? Why did the paper lift up when you blew over it? Air must be pushing these things, but how?

Even before you blew at the balloons, they were surrounded by air pressure. If you tried blowing between them, you disturbed this push in a very special way. Either the air between has stopped pushing as hard or the air on the outer sides is pushing harder. Which do you think happened? Which air did you disturb, the air between the balloons or on the outer sides of the balloons? Can you figure out what happened with the paper? How did you change the air when you blew over the paper? Remember, air can’t suck up anything, but it can push. Did you change the push of air on the top or the bottom of the paper?

Okay, enough questions! Here’s what was going on:

In both the balloon and paper activities, air lost pressure and stopped pushing as hard. This happened because you blew the air, and it had to “squeeze” between or around the objects. As it “squeezed” through, it sped up, lost pressure, and stopped pushing as hard.

The Advanced Explanation...

Now that you know about push and lift, can you see how these forces might relate to airplanes? If we can make air speed up over a wing, the pressure of the air over the wing will drop. The higher pressure air below the wing then pushes the airplane up. How would you shape a wing so that the air moves more quickly over the top than under the bottom?

—-THE WRONG EXPLANATION———————————

Many books state that air speeds up over a wing because it has further to travel than air moving under the wing. This explanation implies that air separates at the front of the wing (point A) and rejoins behind the wing
(point B), but this isn’t true. Air moving over the top of a wing speeds up so much that it arrives at point B sooner than air that travels beneath the wing.

—————————————————————–

Air is a fluid, too, and it behaves like water when it moves through a narrow channel or around an object: It speeds up. When air moves faster, its pressure drops and it pushes less. When an airplane flies, it pushes air out of the way. That air must go somewhere so it “squeezes” between the wings and the surrounding air. The wings are shaped and tilted so that the air moving over the top has less room than the air moving below the wings. Because it has less room, the air moving over the top must speed up more than the air below the wing. As it moves faster, the air on top of the wing also loses pressure and push. The slower moving air below the wing maintains more of its pressure, which pushes the wing, and the plane, up.

An airplane wing affects moving air much like a rock in a stream affects moving water. Remember that the space around the wing is already jammed full of air, so there’s no empty space for more air to move into. As oncoming air hits the wing and moves either over or under it, it speeds up and “squeezes” between the wing and the surrounding air.

One Response to “Lesson: Get a Lift!”

  1. […] Want to build on to this lesson by including more about the forces of flight? Click here. […]

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