show #1212

David drops in on an experiment to test weightlessness. Segment length: 9:30


Insights & Connections



Main activity

Try this


Your fuel gauge is below empty. Both engines of the cargo plane you're piloting have just sputtered and gone silent. The nose of the plane points down and you begin a terrifying dive toward Earth. In a panic, you make your way out of the cockpit and into the back of the plane where your parachute is stored. But a 2,000-kilogram crate is blocking your path. What do you do?

No problem! Since the weight of the crate on the plane's floor is actually zero, you would not have to lift it in opposition to gravity or slide it in opposition to its friction with the floor. The force required to overcome the inertia of the crate would be small enough to allow you to move it by pushing hard with your feet braced against a wall. How is this so?

Let's look at the crate under normal flight conditions. The weight of the crate pushes down against the floor of the plane. What you might not realize is that the floor, which is supported by the airplane's wings and the forces that keep the airplane aloft, also pushes up against the crate. It pushes up with a force equal to the weight of the crate, so inside the plane, you're aware of how heavy the crate is.

When your plane goes into free-fall, the crate is still pulled by gravity just as during a normal flight. But the floor is no longer pushing up on the crate, since it and the crate are now falling freely toward the earth. Gravity is still acting on both the crate and the plane, but inside the airplane, without the upward push from the floor, the crate now seems to be weightless. Both the crate and the pilot will float freely inside the airplane until something--like Earth--stops them.

Astronauts in orbit experience weightlessness just like objects in the falling aircraft. A space shuttle in orbit is actually in a state of free-fall as it travels around Earth.

Hard to imagine? Picture yourself in a small spaceship a few meters above the ground. Now face the setting sun and go in a straight line for about 100 kilometers (62 miles). If you go in a perfectly straight line, you should notice that Earth is curving away from you.

A shuttle in orbit goes so fast that Earth curves "away" just as much as the shuttle falls. The shuttle falls, but never hits the ground!


acceleration change in speed during a certain period of time

ascent going up

descent going down

force that which, when acting alone on an object, causes a change in the motion of the object

gravity force on Earth which pulls all objects toward its center

orbit falling around and around Earth

resistance a force opposing the motion of an object or opposing the forces trying to set an object in motion

weightlessness feeling or being observed as having no weight


Additional sources of information

American Institute of Physics
One Physics Ellipse
College Park, MD  20740-3843
(301) 209-3000
(Ask about Operation Physics)
NASA Education Division
Mail Code F
Washington, DC  20546
(202) 453-1000

Community resources


You have probably noticed an empty feeling in your stomach when an elevator starts its descent. That feeling is a result of a decrease of pressure against your feet and a corresponding change in the tightness of the muscles in your abdomen. Your feet feel less pressure, because the floor of the elevator is going out from under you momentarily. Find out how you could measure this feeling in more concrete terms, and learn which elevator has the fastest acceleration.


  1. Divide into small groups of two or three. Choose some elevators located nearby.
  2. Create a data table like the one below for each of the elevators you are going to test.
  3. Record each of your weights standing still.
  4. Take the scale into the first elevator. Then one student at a time should get the maximum reading on the scale when the elevator starts its ascent and the minimum reading when the elevator starts its descent. You must have a quick eye and should be prepared for approximate results.
  5. Have each student record his or her own data for each elevator tried.
  6. Follow steps 2 through 5 for each elevator.


  1. What happens to your weight when you begin your ascent? How long does the change last?

  2. What happens to your weight when you begin your descent? How long does the change last?

  3. Does a person's initial weight have anything to do with the amount of change recorded?

  4. What kind of change would occur if the elevator cable were to snap? This, by the way, could never happen.


Place a half-gallon plastic milk jug upright and punch a small hole 2.5 cm (1") up from the bottom. Placing your finger over the hole, fill the jug with water. Go to a playground with a friend as an observer. Find a high place and make sure nobody is standing directly below. Take your finger off the hole and drop the jug. What does the observer see happening to the flow of water during the drop?


Sky divers are in a state of free-fall only at the beginning of the jump. Think of ways in which a sky diver could speed up or slow down the descent. Which body positions would be best for speed? Which would be best for hanging in the air?


Does the weight of objects affect how fast they fall? Take 14 pennies. Make two piles of seven. Tape one pile together. Hold one pile in your right hand and the other in your left. Reach both hands up high and cleanly drop the two piles at the same time. The taped pile is at least seven times the weight of each penny in the other pile. Any conclusions?


You know that water falls downhill. What if the whole waterfall falls? Place a half-gallon plastic milk jug upright and punch a small hole 2.5 cm (1") up from the bottom. Place your finger over the hole and fill the jug with water. Go outside and remove your finger to watch the water flow. Now, gently toss the jug up and down without completely letting go. What happens?

Newton's Apple is a production of KTCA Twin Cities Public Television. Made possible by a grant from 3M. Educational materials developed with the National Science Teachers Association.