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172

mass and weight

OLogy Series
physics
card
172

mass and weight

OLogy Series
physics

Mass and weight may seem like the same thing, but in fact these two measurements are very different. Mass is the total amount of matter, or "stuff," in an object. Weight is the force of gravity on an object. Mass always stays the same, but weight can change depending on how much gravity is acting upon an object.

Astronauts on the space station are weightless because they:

are far away from Earth

exercise a lot

are in orbit

Are you right?

### Correct!

When an object like the space station is in orbit, it's actually falling towards Earth without ever hitting it. The orbiting station and the astronaut are in a free fall together, so the weight of the astronaut can't be detected.

What is the same on the Earth and on the Moon?

weight

mass

both

Are you right?

### Correct!

If you were standing on the Moon, your mass -- or the amount of stuff you're made of -- wouldn't change. However, your weight would change because the gravity on the Moon is much weaker than it is on Earth.

In deep space, you could lift up an 11,000 pound Asian elephant with one finger!

or
?

### Fact

An elephant that weighs 11,000 pounds on Earth will weigh virtually nothing in space because of the lack of gravity. But it's mass will stay the same.

You would weigh slightly less standing on a mountaintop than you would at sea level.

or
?

### Fact

You would weigh slightly less on a mountaintop than you would on the ground. The Earth's gravitational pull decreases as you move farther away from its center.

Mass: how much matter, or stuff, something has inside it
Weight: the amount of gravity that is pulling on
an object
How they're measured: mass is measured in kilograms and weight is measured in newtons
Cool fact: Any two masses have a gravitational attraction for one another, and the greater the mass, the greater the pull.

Image credits: Eric Hamilton.