Chapter 3- Universal Gravitation

Question 1

Gravitational field def

Answer 1

Is a region in which a mass feels a force

Is a uniform field
Lines of force are parallel, equally spaced and the arrows are downwards
Size of the force is the same at all points

Question 2

Grav field strength eq

Answer 2

g= Fg (size of gravitational force) / m (body of mass)

Question 3

All objects fall with the same acceleration in…

Answer 3

The same gravitational field

Question 4

Gravitational field strength def

Answer 4

The grav field strength at a point in a grav field is defined as the grav force per unit mass acting on a mass at that point

Question 5

The field is a radial field so the strength…

Answer 5

Decreases with height

Question 6

What is a surface called when it is taken as a place where objects have zero gravitational potential energy?

Answer 6

Equipotential surface

Question 7

Within an equipotential surface…

Answer 7

There is no change in GPE

No work is needed to move an object along such a surface

Question 8

To change between equipotential surfaces…

Answer 8

A change in GPE occurs to move upwards between two adjacent surfaces

(Change is negative)

Question 9

What is newtons law?

Answer 9

States that the force between two objects is proportional to the masses of these objects and inversely proportional to the square of the distance between the objects

Question 10

What is newtons law known as

Answer 10

The inverse squared law

Question 11

Newtons law applies to :

Answer 11

Spherical objects such as planets
And to
Particles

Question 12

Newtons law in an equation

Answer 12

F= Gm1m2/ r^2

Question 13

A body on which the only force acting is the pull of the earth on it (its weight) is said to be in the…

Answer 13

State of free fall

Question 14

What state are satellites in as they circle the earth

Answer 14

They are in the state of free fall all the time

Question 15

There is only one force acting on the satellite which is…

Answer 15

The gravitational attraction of the earth towards the earth’s centre

Question 16

Applying Newton’s second law and his law of gravitation to the satellite gives….

Answer 16

mv^2/r = GmMearth/r^2

As v = 2pie(r)/T

Then…

r^3 = GMearthT^2/4pie^2

r^3 is proportional to T^2
(Kepler’s third law)
The further the satellite is the longer it will take to orbit the earth

Question 17

Free fall is often called

Answer 17

Weightlessness (although weight is acting on it at all times-is just the only force that is)

Question 18

What are radial gravitational fields

Answer 18

Gravitational fields that act around the radius of an object that is spherical

The lines of force become wider as they spread out
Since gravitational potential increases by equal amounts between the equipotential lines then they too become further apart as the distance from the earth increases

Question 19

Gravitational force per unit mass eq

Answer 19

g= Fg/m

g= GmmE/r^2 / m

So…
g= GmE/r^2

mE= the mass of the earth

Question 20

What does the graph of g between r for the Earth look like

Values of g are negative because…

Values of r are positive because….

Answer 20

Is an inversely square relationship

Looks like an exponential

Values of g are neg because r is measured away from the earth but g is measured towards the earth

(Can’t know in detail how g varies below the earths surface)

Question 21

In uniform field what is the gravitational potential difference eq

Answer 21

Vg= g🔺h (g is constant)

Question 22

In a radial field the relationship between gravitational potential and the distance from the centre of the earth is….eq

Answer 22

Vg= -GmE/r

g= GmE/r^2

Question 23

What is the gravitational potential difference between two distances from the centre of the earth….

Answer 23

Vg= -GmE( 1/r1 - 1/r2 )

If one value is close to infinity then it just goes back to

Vg= -Gm/r