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wait V mass why go on a diet when you could go to the moon okay ladies and

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gentlemen we're here today to talk about a new revolutionary diet plan that is [People working out]

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sweeping the nation want to take some pressure off of those aching joints well

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this new plan is the answer you've been looking for you can eat whatever you

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want and there's no exercise required all you have to do is go to the moon now

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you might be asking yourself why do we weigh less on the moon while the answer [Astronaut floating on space station]

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gravity the moon is less massive than the earth so the pull of gravity is

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weaker but our mass hasn't changed a bit we're still made up of the same amount

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of stuff the difference between weight and mass can be a little confusing so

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even though weight versus mass isn't the usual topic of a weight loss infomercial [Man wheeling a whiteboard]

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now let's talk about it anyway in day-to-day life we think of mass and

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weight interchangeably if you go to the doctor's office they don't ask you how [Woman appears in doctors office for weight check]

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much mass you contain no they put you on a scale and you get your weight end of

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story but weight and mass are very different

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things biggest difference while weight depends on gravity mass does not mass is

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measured in units of pounds or kilograms weight will call you the folks in charge

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of SI units weight is measured in Newtons but good luck finding a scale [Man stood on a scale]

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that'll tell you your weight in Newton no we'll take a much closer look at the

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universal law of gravitation some other time but let's just be clear on the

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basics the force of gravity is dependent on two things the masses of the objects

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attracted by gravity and the distance between them increase the masses and you

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increase the attraction of gravity on the other hand if you increase the

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distance between the objects you'll decrease gravity's pulled between the

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objects got it so while absence may make the heart grow [Planets collide]

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fonder distance will make gravity's effect weaker gravity is also why

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astronauts float around in the Space Station or lack of gravity it's not the [Astronauts floating]

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force of gravity isn't acting on the astronauts in fact they're in freefall

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the whole space station is in freefall but its horizontal velocity is so fast [Spacestation orbiting earth]

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that as the earth pulls it toward the planets center the space station is able

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to use that downward pull to maintain its horizontal motion and it needs a

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whole lot of velocity to maintain its orbit the space station is traveling at

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about 17,000 miles an hour which means it travels all the way around the earth

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about 16 times in a 24-hour span so instead of falling down to the planet's [Space station travelling around Earth]

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surface it's falling around the planet well the space station is only about 250

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kilometers off the ground if that distance gravity hasn't changed all that [Man performing star jumps]

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much but the astronauts are weightless because they're falling at the same

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speed as the whole space station think of it like this have you ever ridden a [People sitting on a rollercoaster]

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roller coaster well when you're at the top of the first big hill everything

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feels normal except for maybe your bladder but as you start to go down that

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hill it feels like you're floating you feel yourself pushing up against the [Rollercoaster pushes downwards]

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harness and you feel like you're coming off of your

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well the rollercoaster car and the seat you're sitting on is falling at the same

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rate you are remember normal force occurs when an object's weight like that

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of your toughest deforms a solid surface like a roller coaster seat but if that

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roller coaster seat is also in freefall then you're not going to be deforming [Rollercoaster begins freefall]

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its surface and without feeling that pushback from the seat it feels like

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you're floating so the space station is in freefall and everything in the space

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station is also in freefall which means that there's no normal force to [People working out in class]

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counteract gravity everything's moving the same speed which allows everything

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to float or here's another way to think about it

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imagine you go skydiving everything is great [Plane flying]

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you jump out of the plane fall for a while then pull the cord for your [Man jumps out of plane]

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parachute only someone has pulled a wacky prank on you n instead of a

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parachute a bathroom scale pops out that must bend your buddy Quentin flood a

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prankster well as you're plummeting towards certain doom you decide you [Man with scales in midair]

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might as well see how much you weigh so you put the scale on your feet and try

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to see what it says but because you're not putting any force on the scale it

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won't register any weight at all so you have a good chuckle at another fine [Person laughing in freefall]

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joint like Clint while the space station is only 200 kilometers above the planet

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the moon is about three hundred eighty four thousand four hundred kilometers

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away and way further even at that distance though the gravity of Earth is [Moon orbiting Earth]

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still strong enough to keep the moon in orbit but if you're walking on the moon

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its gravity is what will be affecting you since you're right on its surface [Astronaut bouncing on the moon]

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well the moon is much less massive than the earth but the moon's mass is about

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1.2 percent of the Earth's mass which is why everything weighs way less up there

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and there's less matter to create gravity and for just three easy payments [Astronaut with bag of cash appears]

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of 50 million dollars you too can watch those pounds disappear like magic but

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like I said mass doesn't depend on gravity which makes sense just because

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gravity changes that doesn't mean that what we're made of

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different even on the moon we're still the same humble incredibly smart and [Astronaut picks up mirror on the moon]

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attractive people we've always been and Newton's first and second laws are all

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about mass not weight well part of the first law is that the more mass an

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object has the more inertia it has as well meaning it's harder to change its

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motion and the second law says that the force equals mass times acceleration so

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if it takes 10 Newtons to make a cat accelerate at 1 meter per second squared [Cat accelerating]

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it would take 20 Newton's to make a cat with twice the mass accelerate at the

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same rate now in those SI units we mentioned before the standard unit of

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mass is the kilogram why not the gram we don't know go ask

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some old French scientists and see what they can tell you in French there's [French scientist appears in the street]

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actually some logic to it though a cubic centimeter of water has exactly one gram

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of mass it's also known as a milliliter a thousand grams equals one kilogram and

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a thousand milliliters equals one liter so there's a rhyme and a reason there [Man puts hat on]

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somewhere of course while Pierre and jean-luc were deciding to use the

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kilogram here in the u.s. we decided to just keep on using pounds and ounces and

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not play soccer why because we just have to be different that's why America is

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kind of a hipster when it comes to units of measurement both kilograms and pounds [Hipster girl appears]

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are units of mass we know we know it sounds weird to say I have 130 pounds of

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mass or whatever but the statement would technically be correct we know how to [Man picking up heavy barbell]

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figure out how much something weighs at least here on earth we just pull out a

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scale but what do we use to figure out mass well the best tool for that job is [Man appears in a kitchen]

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a balance like a triple beam balance or you can use a balance that has two sides

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like this double pan balance it's kind of like a sciencv seesaw and then we

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could put something with a known mass on one side and find where it balances with [Man puts 1kg weight on side of balance and head of lettuce on the other]

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something that has unknown mass there's a formula to calculate weight that

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formula tells us that the force of gravity on an object equals the mass

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times the acceleration of gravity it looks a lot like our good ol force

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equals mass times acceleration formula because well they're pretty much this

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we're just swapping out the generic acceleration for the specific

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acceleration of gravity and you might also see F sub G swapped out for a W ie

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wait don't sweat it it's the same thing so [Man standing at table with a scale]

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yeah we measure weight using a scale the scale has Springs that are calibrated

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specifically for Earth's gravity unless you somehow got a hold of a Martian

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scale but nASA says we're not allowed to talk about those all right well you know [Martians jump on a scale]

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the routine you put something on a scale and some kind of readout lets you know

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how much the thing weighs but again all this measuring is being done in units of

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mass what on earth or off of Earth for that matter is a Newton well a Newton is

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a derived SI unit it's not one of the originals one of the big seven it's made

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up of other SI units that come together to form a whole new thing [SI units collide]

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well the Newton is made up of kilograms times meters over seconds squared

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remember force equals mass times acceleration so a Newton which is a unit

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to measure force is just made up of the standard units used to measure mass and

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acceleration so say our cat Milo has a mass of 10 kilograms mostly muscle since [Milo appears from kitty house]

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Milo is most definitely an Earthbound cat we can rely on our standard

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acceleration of gravity to figure out his weight in Newtons 10 kilograms times

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9.8 meters per second squared equals 98 Newtons but just for kicks let's say

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Milo should you know maybe lose some weight well sure we can put him on that [Milo puts on head band and runs on treadmill]

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low-calorie food and see if we can get him exercising again but it would be a

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lot more fun to get him to the moon tada one small step for cat one giant [Milo in rocket to the moon]

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leap for cat kind or something like that well on the moon the acceleration of [Cat walking on the moon]

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gravity is 1.62 meters per second square which means Milo now weighs just about

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16 Newtons if you wanted to convert that measurement to units we'd actually use

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on our home planet while one Newton equals 0.2 to for 809 pounds of force

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which means in terms of earth weight Milo has gone from 22 pounds all the way [Milo walking on the moon]

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down to two point seven pounds but while the scale may tell us he

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weighs less we can see just by looking at him that he hasn't lost any mass so [Milo bounces on the moon]

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he's still 10 kilos in that well this difference in units can get confusing

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which is why it's best to stick to Newtons

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when we're talking about weight at least in the physics world but what happens if [Aliens beam up Milo]

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aliens come along and decide they want a cat on their planet so they take poor

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Milo across the galaxy to wherever they're from let's call it planet steve [Alien spacecraft lands on planet Steve]

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and oddly enough on planet Steve they also use pounds when weighing something

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so when our aliens gleep glorp here to take Milo to the alien veterinarian they [Aliens holding Milo]

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find out that Milo weighs 53 pounds oh well don't worry about it you still

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carry it well and let's face it you weren't the most active cat anyway well

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assuming he didn't lose any mass on his space journey what's the force of

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gravity on planet Steve well boy this whole send the cat to the moon thing [Man puts up lost cat poster]

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that sure has taken a turn let's figure out the gravity here and then we can

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figure out how to get Milo home safe and sound so we know Milo's mass is 10

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kilograms and its weight is 53 pounds how do we find the force of gravity all

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right well remember weight equals mass times gravity so we can rearrange this [Equations appear]

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equation to solve for G but first we need that weight to be in the form of

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Newtons so a little conversion is in order one

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Newton equals point two two four eight oh nine pounds of force or to put it

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another way there is point two two ish pounds for each Newton so if we divide

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53 pounds by that number we find that Milo weighs about 231 Newtons [Milo's weight in Newtons appear]

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now we have what we need to find the force of gravity 231 Newton's of force

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equals 10 grams times G we divide each side of the

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equation by ten kilograms to find that on planet Steve Milo has a gravitational [Milo walking around]

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acceleration of 23 point one meters per second squared which is a whole ton of

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gravity come on Milo let's get you home you're barely functional in Earth's

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gravity well it's important to understand that Newton's our unit of

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force and of weight that's because weight is a force generated by

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gravitational attraction so when we say that we weigh 600 Newtons what we really

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mean is that the gravity of Earth is acting on us to create a force of 600

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Newtons after all weight has to be generated somehow since it's not an

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inherent property of matter it's really a measure of how one object's mass [Earth appears]

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interacts with another object in a gravitational field okay so maybe our

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moon based weight loss plan isn't a great idea after all for it to work [Man discussing moon based weight loss plan]

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long-term we'd have to stay on the moon forever otherwise when you come back to

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earth all those pounds are right back where they started and who wants to live

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on the moon not us all our friends are here plus there really no decent

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restaurants up here [Man standing in hotel room]

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