The difference between mass, density and weight please.
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* **M**ass is an unchanging feature of matter. (measured in kg or a similar unit)
* Weight is the **F**orce caused by gravitational attraction on that object. (**F**orce = **M**ass x **A**cceleration)
* **D**ensity is a measure of mass per volume. (D=M/cm^3 or similar units)
If you measure the weight (tendency to fall towards a high mass object), the weight will change depending on the gravitational properties of that object.
Different big objects will have different numbers for gravitational acceleration. (See chart below for numbers for different planets)
Lets take an example from daily life.
If I have a [10 kg dumbbell for weight training](https://contents.mediadecathlon.com/p1248562/b30a1da767cb801ee9cc906030c3d13d0dfb2e95059f5ffc8d266ee233bdf297/weight-training-dumbbell-kit-10-kg-22-lbs.jpg) at the gym . . .
I can put it on a [spring scale appropriate for that item](https://sc04.alicdn.com/kf/H359cc590539442e68dfacdf69a20b6fbe.jpg) and it will tell me it weighs 10 kg.
If I take those dumbbells and scale to the moon, the exact same procedure would not show as 1.65 kg.
**Note that the scale is calibrated for earth**. It is not telling us that the dumbbells have magically changed to be only 1.65 kg of mass. It is telling us that the force on (stretching or compressing) the spring is the same as if we had 1.65 kg on the scale on earth.
**Our big problem** in understanding this is that we forget that our assumption that weight = mass applies only in very specific situations.
Acceleration due to gravity:
g(Sun) = 274 m/s²
g(Mercury) = 3.7 m/s²
g(Venus) = 8.87 m/s²
g(Moon) = 1.62 m/s²
g(Earth) = 9.80665 m/s²
g(Mars) = 3.71 m/s²
g(Jupiter) = 24.79 m/s²
g(Saturn) = 10.44 m/s²
g(Uranus) = 8.87 m/s²
g(Neptune) = 11.15 m/s²
g(Pluto) = 0.62 m/s²
Mass is fundamental to physical objects. Density is how close that stuff is packed. Weight is how gravity plays with the stuff we call mass.
Some atoms pack different amount of stuff, mostly protons and neutrons. Atom’s electron fields make some take up more space. More stuff in less space=dense, like lead. Spreading stuff out over greater space is less dense, like Styrofoam.
Cool experiment: sink Styrofoam ball 10 meters under water & it will be half the size, but still the same amount of stuff. The pressure made it more dense than at sea level by 1 additional atmosphere of pressure!
Mass is how much shit
Density is how much shit in a given space
Weight is the effect of gravity on that shit
Mass: getting hit by a bus hurts just as much on the moon as on Earth.
Density: dropping a 5 kg rock on your head hurts more than dropping a 5 kg bag of feathers.
Weight: if someone is going to drop a rock on your head, it hurts a lot less if you’re on the moon.
Say you have a sandbox you play in, in your backyard.
Mass: How much sand is in the sandbox, doesn’t matter if you’re in space or on the moon it doesn’t change the actual quantity of sand
Weight: How heavy that sandbox is to lift if you want to move it. Weight will decrease on the moon, or increase on the surface of the sun.
Density: How much space the sand occupies. You could melt the sand, and it would take up less space making it more dense
Mass: How much there is (atoms) of something.
Density: How tightly packed the mass is. (atoms within a given space)
Weight: How strong the force of gravity is pulling on something. This is directly correlated with Mass of both the planet and the object, but not density.
Example: A rock vs a pebble of the same composition. Rock is bigger, so it has more mass, but they will have the same density. The rock will also weigh more than the pebble.
If we somehow squeeze the rock so it shrinks to the same size as the pebble it’s mass hasn’t changed, but it is now very dense, more dense than the pebble (more atoms in a smaller space).
Its weight, however, has not changed. The earth is still pulling on the rock the same as it had before, because the number of atoms in the rock hasn’t changed. The only way to change the rock weight would be to add or remove mass (atoms) from the rock OR move the rock to another planet with a different mass
Mass is a measure of how much matter there is
Density is a measure of how much mass there is per unit volume
Weight is the measure of how hard an object is pulled (force) by a gravitational field
If I have two 100 g objects (mass) and one is 10 cm^3 and the other is 100 cm^3 (volume), then they have two different densities. The 10 cm^3 one has a density of 10 g/cm^3 and the 100 cm^3 object has a density of 1 g/cm^3 . These are two different densities even though they both weigh 100 grams. 1 g/cm^3 is the density of water, and 10 g/cm^3 about the density of silver. Silver sinks in water because it has a higher density.
Weight only applies when you’re in a gravitational field (like here on Earth). Weight is simply mass times gravitational field (g=9.8m/s^2 here on Earth). If I have a 1kg object, it weighs 9.8 N (Newtons, a unit of force). On the moon (g=1.6m/s^2 ), that same 1 kg object will weigh 1.6 N. If you’re out in space (g = 0 m/s^2 ), all objects would be weightless (0 N)
mass – you have a specified unit or Kg, Lb, grams in an object and dosnt change based on location.
density – you have a specific amount of mass of stuff in a define volume of space. this is standardized in things like specific gravity grams/ml or ppg, pounds per gallon major one in my industry.
weight – weight is a factor of gravity, meaning the same mass here and a different planet have a different weight on a scale due to gravitational effects.
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.
“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.
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