Gravity Compilation: Crash Course Kids - Free Educational videos for Students in K-12

Gravity Compilation: Crash Course Kids - By Lumos Learning

Transcript


00:0-1	what goes up must come down a ball you throw
00:02	in the air an apple that drops from a tree
00:05	, even you when you're on a trampoline at someone's
00:08	awesome birthday party . But why , my friends ?
00:11	Let me introduce you to one of the most wonderful
00:14	forces in the universe . It's one we're all experiencing
00:17	right now without even trying . Fasten your seat belts
00:21	because we're going to explore the power of gravity .
00:27	If I told you that you just won the lottery
00:30	, what would you do if you're like me ?
00:32	You jump up and down and scream , And after
00:34	you were done freaking out and jumping in the air
00:37	, you'd land on your feet , right ? But
00:39	why would you land back on the ground instead of
00:42	just floating off into space ? It's because of a
00:48	little something we call gravity . Gravity is what pulls
00:51	everything towards the ground , including you . Without the
00:55	force of gravity , there would be no life on
00:57	earth , air , water , animals . Everything would
01:00	fly off into space . There would be no ,
01:02	you know me know french fries not to think of
01:06	gravity like the invisible super glue that holds our massive
01:09	world together . You can't see it , but it's
01:12	always there . An English scientist named Isaac Newton was
01:15	the first person to seriously study gravity over 300 years
01:18	ago . There's a famous story about him that you
01:20	might have heard . Supposedly , Sir Isaac was hanging
01:23	out underneath an apple tree , thinking probably partly napping
01:27	when an apple fell from the tree and conked him
01:30	on the head . That's when Sir Isaac had an
01:32	a ha moment . Why did the apple fall down
01:35	to the ground and not up or sideways ? He
01:38	realized that a special kind of force , which we
01:40	now know as gravity , was acting on all of
01:42	the objects on Earth , pulling them toward it .
01:45	Once the apple became too heavy for its stem to
01:47	hold it anymore . The gravitational pull of Earth brought
01:51	the apple down onto Newton's noggin . Newton also realized
01:54	it doesn't matter how heavy an object is , either
01:57	whether you're holding an apple or a bowling ball or
01:59	a feather . If you let go of it ,
02:01	that sucker's going down . We're going to make a
02:04	whole video about this later . Basically , he determined
02:06	that what goes up must come down . Sir ,
02:09	Isaac was a pretty smart dude . Okay , So
02:12	you know that if you jump up , you'll eventually
02:14	land back on the ground . And you know that
02:16	an apple drop down will land on the ground to
02:20	. But what if you throw something in front of
02:22	you or to the left or the right mm to
02:28	see how gravity will act , pick up the tennis
02:30	ball or any small round object and hold it in
02:33	your hand . Let's toss it in the air and
02:36	watch it fall to the ground . No surprise here
02:38	. Okay , now pick it up and hold it
02:40	over your head . Let go and watch it fall
02:43	once more again . Not a shocker . Now throw
02:46	it to your left ball down , pitch it to
02:48	the right and watch it go down again . Mm
02:54	, no matter where you throw the ball , it's
02:57	going down . So we've determined that near the surface
02:59	of the earth , where we all are , gravity
03:02	is the cause that produces the effect of all unsupported
03:05	objects falling down . The ball will go up or
03:08	to the left or to the right for a little
03:09	bit , but eventually it's going to be pulled back
03:12	down to the ground . No matter what gravity has
03:15	got a hold on Well , everything . So eventually
03:19	everything that you can think of can be thrown up
03:21	into the air and we'll come back down even if
03:24	you throw it to the left or the right or
03:26	any other direction . That's gravity doing its thing .
03:29	But when you really think about it , which way
03:32	is down exactly ? I mean , the earth is
03:34	round , and there are all kinds of things on
03:37	what we think of as the bottom of the earth
03:40	. So how does gravity keep them from falling off
03:43	? I know a penguin who can answer that question
03:48	Shit . So you know that the earth is round
03:52	and you know that gravity is the force that pulls
03:54	objects down . But if the earth is round and
03:57	there's stuff at the bottom of the earth say a
04:00	penguin in Antarctica , why doesn't gravity pull the penguin
04:03	down off of the earth ? I mean , does
04:06	gravity really pull down when we talk about gravity and
04:13	we say things like up or down , we don't
04:16	mean those things in the sense that you're used to
04:18	in this case , up just means away from the
04:21	Earth and down means toward it . So When you
04:24	hear people say gravity pulls things down to Earth ,
04:27	they really mean that gravity pulls things toward the earth
04:31	. Now think of it this way . Gravity is
04:33	the force of attraction between any two objects made of
04:36	matter , right ? Well , I have news for
04:38	you . You're made of matter , and so is
04:40	the earth . That means you and the Earth have
04:42	an attraction to each other . Oh , you guys
04:46	. Anyway , the scientific argument for gravity is that
04:48	any object that's on or close to Earth's surface and
04:52	is made of less matter than Earth will be pulled
04:55	in by our planet . Stronger gravitational pull . Want
04:58	to do a little demonstration ? Mhm mm . To
05:03	show how Earth's gravity can pull an object like the
05:05	penguin we mentioned before toward it . No matter where
05:08	on Earth that penguin is , all you need is
05:11	a tennis ball and a rubber band . Oh ,
05:13	and your index finger . Now let's pretend the tennis
05:16	ball is Earth and the rubber band represents the force
05:18	of gravity that makes your finger are adorable Little penguin
05:22	just chilling on the surface of the earth . Now
05:25	stretch the rubber band around your tennis ball earth and
05:28	stick your finger under the rubber band . Now try
05:30	to lightly pull your finger away from the ball .
05:33	The penguin is trying to jump off the earth ,
05:35	even though penguins can't fly . What are you doing
05:38	? Penguin . But what happens ? Not much .
05:41	Your finger doesn't get far before the rubber band pulls
05:44	it back toward the ball , right , and the
05:46	effect is the same . No matter where your finger
05:48	penguin is on your earth ball , whether it's at
05:50	the top or the side or on the very bottom
05:53	, the same thing happens . The penguin is forced
05:56	back to Earth , no matter how hard it tries
05:58	to jump off . So what does this mean ?
06:05	It means that no matter where on earth an object
06:07	is , the planet's gravitational pull will draw the object
06:10	toward it . And that's how you should think about
06:12	gravity . It's the force that pulls things toward earth
06:16	. So basically we have gravity to think for the
06:18	fact that penguins stick to the bottom of the earth
06:21	. And I , for one , am grateful .
06:24	I like penguins . Interesting , huh ? When we
06:27	say that gravity pulls down , what we really mean
06:30	is that it pulls everything towards the center of the
06:33	earth . But what if I want to take a
06:34	break from the Earth ? What if I'm an astronaut
06:37	and I want to take a vacation on the moon
06:39	? How can I possibly escape the gravity of the
06:43	earth ? And if I can , What will happen
06:45	as I get closer to the moon ? I guess
06:47	there's only one way to find out . You know
06:52	how many people have actually been on the moon ?
06:54	12 . That's all . But one day we may
06:56	go back there . We have a lot more to
06:58	learn about the moon and space in general . So
07:00	someday , maybe in your lifetime , we'll send astronauts
07:03	out there to study and explore . Do you want
07:06	to be one of them ? If you do ,
07:08	let me give you some helpful tips about a little
07:09	thing called gravity because you're gonna need to know all
07:12	about what gravity is and how it works . If
07:15	you're going to escape the pull of earth and fly
07:17	to the moon now , you already know that astronauts
07:19	can leave the earth , but it takes a lot
07:21	of effort to boldly go where few have gone before
07:23	. But once astronauts reached the speed called escape velocity
07:27	, they're able to overcome the force of Earth's gravity
07:29	and get into orbit around our planet or head on
07:32	over to the moon . So this brings up an
07:34	interesting question . What happens when an object gets away
07:37	from Earth's gravity but close to the moon's gravity ?
07:43	You already know that gravity is the force that keeps
07:46	us from flying off the surface of the earth ,
07:48	and you know that gravity pulls things knocked down .
07:51	But towards the Earth's center , you also know that
07:53	gravity exists between any objects that have mass and the
07:56	greater and objects masses . The greater the effect of
07:59	its gravity or pull on other objects is . But
08:01	there's something more . Remember Isaac Newton , the apple
08:04	tree guy . He determined that the amount of gravitational
08:07	force or pull between two objects also depends on how
08:10	far apart they are , so the farther away something
08:13	is from the earth . The letter will feel the
08:15	pull of Earth's gravity , and the closer it gets
08:17	to the moon , the more it will feel the
08:19	moon's gravity pulling on it . Let's do a little
08:21	pretending to see what happens to something when it moves
08:23	closer to an object that has a really large mass
08:26	and therefore a really strong pull of gravity . Mm
08:31	. If you've ever made a wish on a shooting
08:34	star , you've seen the effect of Earth's gravity pulling
08:36	on an object . Shooting stars , which are actually
08:39	Meteors , occur when pieces of rock break off from
08:41	a passing comet or asteroid and get too close to
08:44	the earth . For example , say this globe represents
08:47	the Earth , and the marble represents a piece of
08:49	space rock that's flying by . You can see that
08:51	there's a huge difference in size between the two objects
08:54	, and if we were to put them on a
08:56	scale , we see that there's a big difference in
08:57	their mass to our model . Earth has a larger
09:00	mass . If the space rock is far away from
09:03	the earth , then it can go on its merry
09:04	way , since it won't be affected by the Earth's
09:06	gravity . But if it gets too close , then
09:09	it and the Earth engage in a bit of tug
09:10	of war . Since both have gravity , they pull
09:13	on one another . It's not much of a fight
09:14	, though . The more massive Earth has a much
09:16	larger gravitational pull , so the rockets caught in Earth's
09:19	gravity and most of the time , it gives us
09:21	a brilliant streak of light we call a meteor .
09:23	But what does this mean for our space travelers ?
09:26	Well , when an astronaut ship takes off for the
09:28	moon and moves away from the earth , the farther
09:30	from Earth it goes , the less it feels the
09:32	pull of Earth's gravity . And as it gets closer
09:35	to the moon , the spaceship begins to feel the
09:37	tug of the moon's gravity more so , even though
09:39	the moon has a smaller mass than the Earth and
09:41	has less of a pull on the ship than the
09:42	Earth does . Once the ship gets closer to the
09:44	moon than the Earth , the moon's gravity pulls the
09:47	ship toward it . And then the astronauts can make
09:49	a safe landing so we can make the argument that
09:55	two things affect the pull of gravity . First ,
09:58	the size of the object . Objects with a bigger
10:00	mass have a stronger pull of gravity and second ,
10:02	the distance between objects . The farther apart objects are
10:06	the weaker , the pull of gravity between them and
10:08	the closer . Together they are , the stronger the
10:10	pull of gravity . All of this means that when
10:11	the day comes that you're flying a spaceship to the
10:13	moon . You just have to escape Earth's gravity and
10:16	then get close enough to the moon to enter its
10:18	gravity . Remember that when you're grown up and you're
10:21	welcome . If you want to thank me , you
10:22	could just name a crater or something after me when
10:24	you get there . So here's what we know so
10:26	far , whether on earth or in space , anything
10:29	that has mass will exert the force of gravity .
10:32	And on Earth , everything falls towards the middle of
10:34	the earth at the same rate . But hold up
10:36	a sec . You've probably noticed that if you drop
10:39	a piece of paper or a feather , it takes
10:42	longer to reach the ground , then something like a
10:44	rock or a ball . So what's up with that
10:46	? It's time to investigate . I don't care who
10:53	you are . If you live anywhere near this planet
10:55	, then you're no stranger to gravity , the force
10:58	that affects every object on Earth and beyond because of
11:01	gravity , whether you're an astronaut on the international space
11:03	station or an ordinary , clumsy , earthbound human who
11:06	happens to drop her books a lot , all things
11:09	caught in our planet's gravity will in some way have
11:12	the potential to fall to Earth . But objects fall
11:15	differently , right ? Like when I knock a piece
11:16	of paper on my desk , it takes a lot
11:18	longer to fall to the ground . Then if I
11:20	knock a book off my desk , So what's up
11:22	with that ? What do things seem to fall at
11:23	different speeds on Earth ? Well , we already know
11:30	that all objects have mass . They have a certain
11:33	amount of matter in them . And when gravity pulls
11:35	on an object , it gives the object . Wait
11:38	now , a long time ago , people used to
11:40	think that heavier things fell faster than lighter things because
11:43	that's what our senses told us . I mean ,
11:45	it certainly looks like the book falls faster than the
11:47	piece of paper . And why would we expect anything
11:49	else ? That would be like dropping a hammer and
11:51	a feather and expecting them to hit the ground at
11:53	the same time ? Except the thing I just said
11:55	about the hammer and the feather . Someone did actually
11:59	try that , and they did both hit the ground
12:01	at the same time . It just didn't happen on
12:04	Earth . True story . When astronaut Dave Scott was
12:07	on the moon in 1971 he did an experiment where
12:10	you dropped a falcon feather and a hammer from the
12:12	same height , and they hit the ground at the
12:14	same time . Now , how can that be ?
12:17	If you drop a hammer and a feather on Earth
12:19	, the feather would take a lot longer to reach
12:21	the ground . So what does the earth have that
12:24	the moon doesn't , For one thing an atmosphere .
12:26	The gases that make up Earth's atmosphere push against objects
12:29	as they fall , and the push of the air
12:31	against the falling object causes friction . We call that
12:34	friction air resistance . So on Earth , the feathers
12:37	flat , fluffy shape makes it run into more air
12:39	resistance than the hammer does . This makes it fall
12:41	more slowly than the hammer , but since the moon
12:43	has almost no atmosphere , there's almost no air resistance
12:47	. So the two objects fell at the same rate
12:49	. So it seems to me that it's the resistance
12:51	of air , pushing against objects that really affects how
12:54	fast objects fall . And that means that it's experiment
12:57	time . Yeah , mhm . But you don't have
13:03	to go to the moon to do this , so
13:04	don't pack your bags or anything . All you need
13:06	are two pieces of paper that are the same size
13:09	. Crumble one of the pieces into a tight ball
13:11	and leave the other one smooth and flat . Now
13:13	drop each piece of paper from the same height ,
13:15	Let's say a meter and then write down in a
13:18	table how long it takes each piece to reach the
13:20	ground . You'll see it takes a flat paper longer
13:22	than the crumpled paper to hit the floor . This
13:25	is evidence that an object shape affects how fast it
13:27	seems to fall to Earth because the two pieces of
13:30	paper are exactly the same . They have the same
13:33	mass , but air resistance makes a flat paper seem
13:36	to fall more slowly than the crumpled paper . So
13:43	based on the results of our experiment , we can
13:45	say , at least here on Earth , objects appear
13:47	to fall at different rates , not because they have
13:50	different masses or weights , but because of air resistance
13:53	, the force that the Earth's atmosphere has on objects
13:56	as they fall . So there you have it .
13:58	Gravity is the force that's exerted by everything that has
14:02	mass , and it's felt by everything equally , even
14:05	though falling objects on earth might not always look like
14:08	that's the case . I mean , if you don't
14:10	believe me , you can go to the moon and
14:12	do the old hammer and feather experiment for yourself or
14:15	you can just trust me . If you enjoyed this
14:17	, check out the rest of our channel and subscribe
00:0-1	.

Summarizer

DESCRIPTION:

Maybe you'd like to just hear about one topic for a while. We understand. So today, let's just watch some videos about Gravity. We'll learn about why we don't fly off into space, what mass has to do with it, how does air resistance work, and why gravity is different on the moon. In this compilation,

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