Mass explanation: I’ve always been told that mass was not the same as weight, and that grams are the metric unit of mass. But grams are a measurement of weight, so am I stupid, was it was explained to me wrong, or is science just not make sense?
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Mass is a measure of how much “stuff” there is. Everything is made from protons and neutrons and they the more of them an object has the more mass it has. (Approximately, I am igboring electrons (very light) and energy, because Einstein told us energy is also mass)
The more mass something has, the harder it is to change the objects velocity. It’s much easier to push a 1 kg rock than a 1000 kg rock. This resistence to the change of velocity of an object is known as its “inertial mass” and is the mass in Newton’s famous equation F = ma
It also happens that how hard gravity pulls on an object depends on how much stuff there is to pull on. (And conversely, how hard something pulls on something else, that is how much gravity an object “creates” also depends on how much stuff it is pulling with) and thus it’s mass. How hard gravity pulls on an object is known as the “gravitational mass” It may seem logical and intuitive but it’s actually quite difficult to explain why the inertial mass and gravitational mass are exactly the same, it’s an advanced topic. But they are exactly the same. This is part of the reason there is such a great deal of confusion about mass, it’s playing two different parts!
The other reason is that if you want to measure the mass of an object it is very simple to do. You could measure exactly how hard you’re pushing something and how fast it then moves, but this is quite complicated. We also know that gravity pulls more massive things harder. If I put two rocks on a table the heavier rock will push on the table below it with more force because gravity pulls on it harder. And it is very easy to measure forces! And thus if I know that force I can do a little calculation and know the mass of the rock. This practice has become so common that the measurement devices (scales) don’t even tell us the force they measure, they immediately convert it to kilograms. They tell us how many kilograms would produce that force they measure. That force is thus not exactly the same as the mass, that is the weight.
Importantly, weight is the force measured that is produced by an objects mass in gravity. This weight is thus different in places with a different strength of gravity. On Jupiter your mass would be the same as on earth, you are still made from the same stuff, but gravity would pull on you more strongly, thus you would weigh more.
So weight and mass are different things, but for most things it’s the same. A weight of 1 kg is the force exerted on a surface by a mass of 1 kg under Earth’s gravity
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