# The difference between mass, density and weight please.

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The difference between mass, density and weight please.

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Mass: how much stuff there is.
Density: how tightly packed that stuff is.
Weight: force exerted by that stuff due to gravity.

Mass = density/volume

Density = mass/volume

Weight = mass x gravity

Not exactly eli5 but just think about these equations for a minute and it’ll click

Mass is a measure of how much “stuff” something has.

Weight is a measure of how much *force* gravity is exerting on the “stuff”.

If you got on a rocket and flew to the moon, your *mass* wouldn’t change; you’re still made up of the same amount of stuff. But your *weight* would decrease, because gravity on the mood is weaker than it is on the earth.

Density is a measure of how much “stuff” something has compared to it’s volume. If we blow up a balloon, the amount of “stuff” that makes up the balloon doesn’t change, but the *volume of space* that stuff occupies changes. Objects with low density have a big physical size, but not as much “stuff” and objects with higher density.

“Weight” assumes a certain gravity. The “Weight” of an object changes depending on whether you’re on the Earth, the Moon where it’s lower, or in orbit where it’s always 0.

“Mass” takes what “weight” is supposed to mean, but without the gravity context. A cube of water 1 meter on each side has a mass of 1000 kg, regardless of gravity. Even in orbit where everything is “weightless”, a big barrel of water still feels heavy if you tried to bench press it. A car has high mass, which means rolling it down a level road is hard to do by pushing it even in neutral, vs a small child’s wagon which has much less mass on the same road. Gravity isn’t involved in this situation.

“Density” is the fraction of mass divided by volume of space occupied. From our cube of water, we have a density of 1 gram per cubic centimeter, or 1 tonne per cubic meter, which are both the same number. Air is much less dense, weighing a few grams per cubic meter. Lead is much more dense, and even a ball of lead the size of a baseball would weigh many many pounds.

Mass is, essentially, how many protons, neutrons, and electrons something contains. It’s how much physical matter is present.

Density is a function of volume and mass – how much physical matter is present in how much space. 10 pounds of physical matter in a one inch cube is far denser than 10 pounds of physical matter in a one foot cube, for example.

Weight is a function of mass and gravity (acceleration to be more precise). Because we developed all our measurements on earth one pound of mass is more or less equal to one pound of weight, because it’s based on earth’s gravity. Using the same unit (pound) for both is confusing, but for the average person in a day-to-day context mass and weight are functionally identical.

But one pound of mass is only about 1/6th a pound of weight on the moon, because there’s less gravity up there.