Refer to the following caption.

Four Forces of Flight

Force 1: Gravity

Sir Isaac Newton, an English scientist, observed the force of gravity when he was sitting under a tree and an apple fell on his head!

The force of gravity attracts things towards the center of the earth. For things to fly, they need to have lift (Force #2) more than the force of gravity.

New Words:

  • Force - Putting something into motion or changing its motion.
  • Gravity - Force that tends to draw all bodies in the earth's sphere to the center of the earth.

Activities:

  • Jump up into the air - and stay there! What happens? Do you know of any place that does not have gravity or much less gravity? (Hint: There's a picture on this page that tells you where.
  • Drop a pencil, rock and a ball. What happens? What does this mean for bigger and heavier airplanes?
astronaut

Force 2: Lift

Daniel Bernoulli, a Swiss scientist, observed that the faster that a fluid (and air is a fluid!) travels over a surface, the less time it has to push on the surface.

Airplane wings are designed with a higher top, that makes the air travel faster over it. This creates lift.

The force of lift makes things rise. For things to fly, they need to have lift (Force #2) more than the force of gravity (Force #1).

New Words:

  • Force - Putting something into motion or changing its motion.
  • Lift - Force that brings strength to raise or to try to raise something.

Activities:

  • Walk over to a wall. Push on it. Now turn and walk alongside the wall and try to push on the wall at the same time. What happens? Walk faster, now what happens?
  • Hold a piece of paper just under your lower lip. Blow hard across the top of the paper. What does it do? (As the air moves faster across the paper it can't press as hard down on the paper.)

Force 3: Thrust

Whenever you push or move something, you are using thrust. Different kinds of engines (jets, rockets, pedals, your arm) create thrust.

The force of thrust moves items away from their current position.

For things to fly from place to place, they need to have thrust (Force #3) more than the force of drag (Force #4).

New Words:

  • Force - Putting something into motion or changing its motion.
  • Thrust - Force that moves things forward.

Sir Isaac Newton, an English scientist, observed that every action has an opposite and equal reaction.

In these activities, you’ll also get to see "Newton's First Law of Motion"!

Activities:

  • Blow up a balloon and hold the opening tight. Now release it. What direction did the balloon go? What direction did the air go?
  • Make a paper airplane, and fly it. What supplies the thrust to the airplane (or power)?

Force 4: Drag

When you push or move something, it can be easier or harder if you are pushing it over carpet, a hard floor, grass or dirt. When you ride in the car, to stop the driver puts on the brake. In a boat, to stop someone throws out an anchor. All of these things that stop motion are forms of drag.

For things to fly from place to place, they need to have thrust (Force #3) more than the force of drag (Force #4).

When surfaces move against each other, that causes friction. Air is one surface and the airplane’s skin is another, so this creates friction. Friction is the most common kind of drag in flying.

New Words:

  • Force - Putting something into motion or changing its motion.
  • Drag - Force that works against motion, like a brake.
  • Friction - Resistance of motion against of two moving things or surfaces that touch.

Activities:

  • Take a closed umbrella and hold it behind you and run. Now open the umbrella, hold it behind you and run. What happens?
  • At the same time, drop two identical sheets of paper, one flat and one crumpled into a ball. What is the difference? What does this mean on how we design an airplane?