The difference between mass, density and weight please.
In: 11
Mass is how much shit
Density is how much shit in a given space
Weight is the effect of gravity on that shit
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!
* **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
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