6.3.4 Weightlessness

Suppose the elevator cable breaks and the elevator, along with the man and his scale, plunges straight down in free fall! What will the scale read? When the free-fall acceleration $a_{y} = - g$ is used in Equation 6.10, we find $w = 0$ . In other words, the man has no weight!

Suppose, as the elevator falls, the man inside releases a ball from his hand. In the absence of air resistance, as Galileo discovered, both the man and the ball would fall at the same rate. From the man’s perspective, the ball would appear to “float” beside him. Similarly, the scale would float beneath him and not press against his feet. He is what we call weightless. Gravity is still pulling down on him—that’s why he’s falling—but he has no sensation of weight as everything floats around him in free fall.

A photograph of an astronaut floating inside a spacecraft. Note: Astronauts are weightless as they orbit the earth. — Astronauts are weightless as they orbit the earth.

But isn’t this exactly what happens to astronauts orbiting the earth? If an astronaut tries to stand on a scale, it does not exert any force against her feet and reads zero. She is said to be weightless. But if the criterion to be weightless is to be in free fall, and if astronauts orbiting the earth are weightless, does this mean that they are in free fall? This is a very interesting question to which we shall return in Chapter 8.