okay all right now mass let's talk about mass okay and by mass what I mean is the total amount of material contained in a planet okay the total amount of material contained in a planet and this could either be small or large okay a high mass or a low mass right so which group of planets would you guess probably have more material inside would you guess that the jovian planets have more material inside or would you guess that the terrestrial planets have more inside you'd probably guess Jovian right because they're bigger and we typically think of bigger things having more inside now I'm not gonna say if that's right or wrong let me ask you this is the amount of mass something has something you can see is the matte the amount of material inside of something something you can see by looking at it yes or no so it turns out it's it's not something you can see right it's not something you can see let me let me put it this way check me out look at me look at me my mass would be how many kilograms I am right it's the amount of material inside of me you can't know that right you can't know what's going on inside of me you don't know how much in here is is is is fact or how much is straight muscle right here's a hint it's mostly fat it's mostly fat in here there's not a lot of ripped Ness there's no there's no definition here but technically you can't know what my mass is just by looking at me right so what would you have to do to figure out how many kilograms I am what would you have to do what you to do with me to figure out what my mass is yeah you're gonna have to figure out some way to measure it you're probably you're gonna yeah you're probably gonna put me on a scale right you're probably gonna put me on a scale in order to measure my mass because here's the thing why can't you just know the mass from looking at something well we said that the mass is the amount of stuff contained in that object but what's the only part don't overthink this what's the only part of an object you can see when you look at it any object what's the only part you can actually see yeah the outside the outside right you could only see the outside the outer parts of any object so when you're looking at me you see my skin and like my shirt right you don't see what's inside I could be totally hollow inside maybe I'm a fake person maybe I'm just a hollow shell of a human being and it's all air inside of here that wouldn't look any prynt then if I was just an actual human being right as long as you made the outside look right right so we can't tell what's inside from looking at it so we have to figure out a way to measure it okay so check this out so somebody says they're behind in the stream I'm sorry about that but just keep on following along you're okay now check this out if you wanted to find my mass you'd put me on a scale can we put Jupiter on a scale can we put Jupiter on a scale no just way too big it would take way too much money to make a scale that big and when you get that big things are gonna get weird we're trying to put it on that actual scale so we got to figure out some other way to indirectly figure out the mass of these planets and luckily for us there is a way okay because mass causes a force which force does mass cause if something has mass somebody's on the right track here somebody's on the right track if something has mass what force does that mass create gravity and somebody said Kepler's third law essentially we're using Newton's law which which is again a more complete way to describe Kepler's laws so you're on the right track but we can use the gravity of a planet to determine how much mass it has because let's see if we can put this together if a planet has more gravity does it have more or less mass if a planet has a stronger gravity than the earth does it have more or less mass than the earth more okay so basically if we can figure out how strong the gravity on a planet is we can figure out how much mass it has because more fati means more mess okay and there's a few ways we can do that we can uh we can drop things on the planet so that we can measure how fast they fall and by looking at how they fall we can figure out how much gravity they have and we can just look for things that are already orbiting the planet so what's the thing that could orbit a plant what do we call big balls then orbit these planets will we look at how many objects orbit we'll talk about how many how many moons each of these has eventually we'll get there but moons if we look at the moons of these planets not all the planets have moons but if a planet has a moon the speed of the orbit of your moons is determined by how much gravity you have the more gravity that planet has the faster those planets will orbit at the same distance as from other planets so in terms of gravity it turns out here we go the jovian planets have a higher gravity than we do let me put that on here so relatively high gravity and terrestrial planets are considered to have low gravity so a planet like Earth earth is considered to be a low gravity planet we don't typically think of this as being low gravity because this is the gravity we're used to right this is a gravity the gravity here is strong enough to kill a human being but that's still considered low compared to the amount of gravity that the jovian planets have at the same distance right so putting that together were we right that jovian planets have more mess yes or no we're based on this information were we correct that jovian planets have more mass that's what that was our guests yes we were correct right we were correct here okay so jovian planets because of their high gravity means they have a high mass whereas terrestrial planets because of their low gravity they have a low mass okay my point though instead of just going straight from the guess at saying a we're right is pointing out that just because something is bigger doesn't mean it necessarily has more mass that's not gonna always be the case but in terms of the planets the bigger ones are a higher mass okay so we were right now some of you guys did guess that the terrestrial planets have more mass and I saw a lot of people talking about that and they're like oh but the terrestrial planets have a lot of rocks and a lot of you guys were saying the jovian planets have a lot of gas okay but here we're not talking about what kind of mass you have we're talking about how much of it you have okay so what you were thinking of instead of mass was density okay density when we're talking about the density of something what are we basically talking about if you say something is very dense what are you saying about it if something is very dense what does that mean like what does that mean in like a normal how could you explain that to a little kid what does it mean to be dense it restart this while you guys are answering that compact that's a good way to put it that's a good way to put it if something is dense it is packed tight right and if something is low density it is not packed tight it's very very spread out so your density has less to do with the total amount of material you have and more to do with the type of material you have okay it's very very thick you can sort of think of thick but yeah it's just really really packed tight that's what being dense means so density depends on - thanks okay it depends on two things one of them is your size and one of them is your mass okay your size and your mass combined give you your density okay to help you understand what I mean let's say I had them put this aside for a second let's say I had two buckets okay two buckets that were the exact same size okay and they were identical buckets and in one of those buckets I put let's say I put three rocks in that bucket but in this one I packed in that one so in this area I only have three rocks but in this one I have a lot more than three rocks so which one of these let's call this a let's call this B which bucket has a higher density right now they're given there that they have the same area they have the same size but B has more rocks so B would be denser so if I pack more mass into the same volume the same size then that would make the density go up so in general if we're if the size is the same more mass would make your density higher right because your you would have to pack it in tighter to get the higher mass in that size right but on the other hand size also matters here when you're talking about distance or is it density right if you were to take an object let's say you were take to take one and you were to puff it up to a much bigger size if you took one object without changing what it's made out of and you just blew it up to a much bigger size what's going to happen to the density if you take that object and spread it out is the density going up or down yeah the density is going down or lower right so in terms of size bigger size means lower density okay so if we put these together bigger mass would mean a higher density as long as the size was the same increasing size though brings your density down and the reason that those are both related is another way to say this density is to say it's the amount of mass you have per size mass over volume okay so here we go if we go back to our list OOP this is not our list if we go back to our list if we were just looking at mass we said higher mass gives you a higher density in general if they are the same size but are the terrestrials and the Jovians the same size are the terrestrials in the jovian planets the same size no right no so if they were the same size if they were the same size then Jovians having higher mass would mean that they have a higher density because if they were the same size that higher mass would mean more stuffs packed into the same area right but Jovians are also much much bigger and in fact the difference in size is so large that even though Jovians have more material than us they are spread so far out that their density is low okay so let's add that onto here this is the first thing that the terrestrial planets get to win at jovian planets are low density whereas terrestrial planets are high density and again it's because of the kind of material that these planets are made out of what kinds of material are terrestrial planets made out of let's see if you guys can throw me out some types of stuff what kind of stuff is a terrestrial planet mostly made out of that gives it such a high density I don't need an exact type of material but what kinds of stuff what's a terrestrial planet like Earth made out of rock yep terrestrial planets have a lot of rock up ground that makes sense you're basically saying rock rock metal all of these things we can think of a terrestrial planet as mostly solid and we have some liquid rock inside of our planet but even that liquid rock is actually very close to being pretty solid okay for most of it a lot of it so mostly solids terrestrial planets mostly solid