Gravitational Field Strength Bozeman Science English (auto-generated) English

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Spanish tykylebjorn

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[Music] hi it's mr. Andersen and this is ap

physics essentials 25 it's on

Hi. It's Mr. Andersen and this AP Physics essentials 25. It is on gravitational field

gravitational field strength which is a measure of the gravitational force placed on an object that's in a

strength which is a measure of the gravitational force placed on an object that is in a gravitational

gravitational field and so you know that the moon orbits around the earth and

field. And so you know that the moon orbits around the earth and stays there because of

stays there because of this gravitational field and so if we place it in orbit watch how the force on those

this gravitational field. And so if we place it in orbit, watch how the force on those

two objects remains constant the gravitational field strength is the same

two objects remains constant. The gravitational field strength is the same. But if we were

but if we were to play around with this Paet simulation if we move the moon

to play around with the phet simulation, if we move the moon closer to the earth, you

closer to the earth you can see the force is increasing it has greater strength and as we move it away it

can see the force is increasing. It has greater strength. And as we move it away it becomes

becomes less how else could we change the gravitational field strength well we

less. How else could we change the gravitational field strength? Well we could increase the

could increase the mass of the moon it's a greater force we could increase the mass of the earth as well and there's

mass of the moon. It is a greater force. We could increase the mass of the earth as well

going to be a greater gravitational field strength and it's going to have

and there is going to be a greater gravitational field strength and it is going to have catastrophic

catastrophic consequences when we put it in orbit and so remember any object that

consequences when we put it in orbit. And so remember, any object that has mass is going

has mass is going to generate a gravitational field and those field lines are going to point to the center

to generate a gravitational field. And those field lines are going to point to the center

of that object and so any object and we'll just deal with spherical objects

of that object. And so any object and we will just deal with spherical objects in AP Physics

in AP Physics one is going to have a gravitational field that's going to

1, is going to have a gravitational field. It is going to become greater the closer we

become greater the closer we come to that object and so if you want to calculate the gravitational field

come to that object. And so if you want to calculate the gravitational field strength,

strength this equation works and it was developed by Sir Isaac Newton and it

this equation works. And it was developed by Sir Isaac Newton. And it really only has

really only has those two things that we shot and we saw in that video it's the mass of the object and then the radius

those two things that we saw in that video. It is the mass of the object and then the

or the distance between that object and a point now you might say there's three

radius or the distance between that object and a point. Now you might say there are three

things in this equation the first one is a gravitational constant we've lots of

things in this equation. The first one is a gravitational constant. We lots of times

times refer to that as big G but the other two things that are going to affect the gravitational field strength

refer to that as big G. But the other two things that are going to affect the gravitational

are the mass of the object and then the radius or the distance from the object

field strength are the mass of the object and then the radius, or the distance from

and so in this class you should be able to calculate the gravitational field

the object. And so in this class you should be able to calculate the gravitational field

strength of an object or sitting in the surface of a really large object like

strength of an object or sitting on the surface of a really large object like the planet.

the planet and so gravitational field strength this is our equation right here

And so gravitational field strength, this is our equation right here, there are three

there are three parts to it and so if we're measuring the gravitational field strength at a point separated from that

parts to it. And so if we are measuring the gravitational field strength at a point separated

object we need to know the mass of the object we need to know the radius and

from that object, we need to know the mass of the object. We need to know the radius.

know this that when we're looking at the radius it's not from the surface of the

And note this, that when we are looking at the radius it is not from the surface of the

object its from the center of mass of both objects in this case one is just a

object. It is from the center of mass of both objects. In this case one is just a point.

point and then the last one is going to be the gravitational constant or big G and that's just six point six seven

And then the last one is going to be the gravitational constant or big G. And that is just 6.67 times

times 10 to the negative 11th and then we got a bunch of Units coming in after

10 to the negative 11. And then we have a bunch of units coming after that. And so let

that and so let me give you an example problem let's say I want you to figure

me give you an example problem. Let's say I want you to figure out the gravitational

out the gravitational field strength of a baseball you could imagine it's gonna

field strength of a baseball. You can imagine it is going to be really, really small. There

be really really small there's not much mass in it but if you want to solve this problem I haven't given you enough

is not much mass in it. But if you want to solve this problem I have not given you enough

information you need to know what's the mass of that object it's point one four

information. You need to know what is the mass of that object. It is 1.45 kilograms.

five kilograms and you also have to know how far away is it and let's say it's it's two point zero meters and so you

And you also have to know how far away is it. And let's say it is 2.0 meters. And so

maybe have forgotten what big G is so we'll put that right up there six point

you maybe have forgotten what big G is, so we will put that right up there, 6.67 times

six seven times 10 to the negative 11th and so you may want to pause the video right now and try to solve this problem

10 to the negative 11. And so you may want to pause the video right now and try to solve

or you could just watch me do it I'm gonna take those three values and I'm

this problem. Or you could just watch me do it. I am going to take those three values

gonna place them into my equation so I'm taking the big G times the mass divided

and I am going to place them into my equation. So I am taking the big G times the mass divided

by the radius squared and so when I solve that I get a gravitational field

by the radius squared. And so when I solve that I get a gravitational field strength

strength or a G of 2.4 times 10 to the negative 12 Newton's per kilogram if we

or a G of 2.4 times 10 to the negative 12 newtons per kilogram. If we cancel out all

cancel out all those units we've got Newton's on the top we've got kilograms

of those units we have got newtons on the top. We have kilograms on the top. But we

on the top but we've got kilograms squared on the bottom so we're gonna end

have kilograms squared on the bottom. So we are going to end up with one kilogram on the

up with one kilogram on the top and then the meter squared are going to cancel out and so that's going to be the

top and the meters squared are going to cancel out. So that is going to be the gravitational

gravitational field strength of the baseball incredibly small but it's still

field strength of the baseball. Incredibly small. But it is still there. Let's say we

there let's say we're to do this can you figure out the gravitational field strength of the earth so we're sitting

were to do this. Can you figure out the gravitational field strength of the earth? So we are sitting

on the surface of the earth can you figure out what's the strength of that

on the surface of the earth. Can you figure out what is the strength of that force pulling

force pulling you or holding you on the planet well again you'd need two more

you or holding you on the planet? Well again you would need two more things. We are going

things we're gonna need to know the mass of the earth and it's pretty massive 5.97 times 10 to the 24th kilograms and

to need to know the mass of the earth. And it is pretty massive, 5.97 times ten to the

you also need to know how far are you from the center of the earth what's the

24 kilograms. And you also need to know how far are you from the center of the earth.

radius of the earth and it's six point three seven times ten to the six meters and so to solve this problem you're

What is the radius of the earth? And it is 6.37 times 10 to the 6 meters. And so to solve

going to do the same exact thing we're

this problem you are going to do the same exact thing. We are going to plug it into

gonna plug it into those equation those values and again it's worth doing but if

those equations, those values, and again it is worth doing. But if you do this, you are

you do this you're going to get a value that you've seen before the gravitational field strength is

going to get a value that you have seen before. The gravitational field strength is going

going to be 9.81 Newton's per kilogram and so that is going to be the

to be 9.81 newtons per kilogram. And so that is going to be the the gravitational field

gravitational field strength as we get close to the planet again it's also numerically equal to the acceleration

strength as we get close to the planet. Again it is also numerically equal to the acceleration

due to gravity on our planet and you might say it's going to be the same

due to gravity on our planet. And you might say it is going to be the same everywhere

everywhere on our planet but it's not if you look at the gravitational field

on our planet. But it is not. If you look at the gravitational field strength on our

strength on our planet and this is a NASA image it's going to vary depending on where you are because the earth isn't

planet, this is a NASA image, it is going to vary depending on where you are, because

consistent it's not a consistent sphere with consistent density it's going to

the earth is not consistent. It is not a consistent sphere with consistent density. It is going

have differences in latitude and therefore the distance from the center

to have differences in latitude and therefore the distance from the center of the earth.

of the earth there's going to be geological differences what the earth is

There is going to be geological differences. What the earth is made up of. And so we can

made up of and so we can study the gravitational field strength in different areas and it tells us a lot

study the gravitational field strength in different areas and it tells us a lot about

about what the earth is actually made of and so did you learn to calculate the

what the earth is actually made of. And so did you learn to calculate the gravitational

gravitational field strength of an object a certain distance away and did you figure out how to approximate the

field strength of an object a certain distance away? And did you figure out how to approximate

gravitational field strength if you're sitting on the surface of a really large

the gravitational field strength if you are sitting on the surface of a really large object?

object it's the same equation it's pretty easy and I hope that's helpful [Music]

It is the same equation. It is pretty easy. And I hope that's helpful.

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