physics - grav fields

in a field, what type of force is felt/present

non contact force

which objects do gravitational fields affect?

all objects (as all objects have mass)

what law does gravitational force follow

inverse square law

in grav fields, the force exerted is always _____

positive

what is newtons law of gravitation

the gravitational force between 2 masses is directly proportional to the product of their masses and is inversely proportional to the square of the distance measured between their centres 

what is the equation for gravitational field

note:

in the data sheet, it has a (-) in the front.

this is purely for the physics.

the “-” is added to indicate that work must be done to separate the 2 masses, since they are attracted to each other, and wont just repel or separate by themselves

draw the gravitational field lines for a uniform and a radial field

when can a radial filed be considered uniform? (near where)

near the surface of the planet

what is the verbal definition of gravitational field strength.

when does this vary, and when is it constant

the force per unit mass exerted by a gravitational field on an object

varies in a radial field, and remains constant in a uniform field

what are the 2 equations for gravitational field strength?

what is the symbol and unit for gravitational field strength

which of the 2 is used in general

which of the 2 can ONLY be used in a radial field?

gravitational field strength symbol = g

units of gravitational field strength = Nkg^-1

the one on the left can be used in general

the one on the right can only be used in a radial field

what is the equation that links density, gravitational field strength and radius?

what equation is used to find the neutral point?

what is the verbal definition of gravitational potential.

what is its symbol

what units does it have

gravitational potential (v) is the work done per unit mass against a gravitational field, to move an object from infinity to a given point

units: Jkg^-1

what is the value of gravitational potential at infinity

0

is gravitational potential always negative? why/why not

yes

as you move from infinity towards a given point, energy is released, as the grav potential is reduced (because less work is being done to move the point away from the field)

if given the individual potentials, how can u find the total potential and why does this work

sum the individual potentials

this can happen because potential is scalar

what is the gravitational potential equation, for a radial field only?

what is the equation to find work done when moving an object in a gravitational field. what does the m in the equation represent

is work done when moving along an equipotential?

NO. 0 work is done

draw the graph of gravitational potential (v) against r

can gravitational field strength be found from the graph of v against r?

if so, how?

yes

the negative of the gradient (gradient multiplied by -1) is the gravitational field strength.

gradient can be found using tangent

using the equation, (for a radial field), based on the graph how do you find the change in potential?

what is the equation for gravitational field strength based on the graph of v against r

draw the graph of gravitational field strength against r

what does the area under a graph of gravitational field strength against r represent

gravitational potential difference (delta v)

what is keplers third law in words

the square of the orbital period (T) is directly proportional to the cube of the radius

derive keplers 3rd law

what is the total energy of an orbiting satellite made up of?

is it always constant?

made up of its kinetic and potential energy

yes, it is always constant

what is the definition of the escape velocity?

the minimum velocity an object must travel at in order to escape the gravitational field at the surface of a mass

how do we find the escape velocity

make kinetic energy = gravitational potential energy and then just rearrange

what is a synchronous orbit?

it is an orbit where the orbital period of the satellite is equal to the rotational period of the object that it is orbiting

what is the orbital period of a synchronous satellite orbiting earth

would have an orbital period of 24 hours

do geostationary satellites follow a specific geosynchronous orbit?

if so what is it

yes they do. their orbital period is 24 hours

geostationary satelites always stay above the same point on earth, because they orbit directly _____ the _____

above the equator

why are geostationary satellites useful

can send TV and telephone signals, as is always above the same point on earth

use keplers 3rd law equation to calculate the radius of the geostationary satelite

do low orbit satellites have lower or higher orbits in comparison to geostationary/geosynchronous satellites?

lower orbits

what does travelling in lower orbit mean for low orbit satellites compared to geostationary satellites?

how does this affect their orbital periods?

they travel much faster

this means their orbital periods are much smaller

what are the 3 uses of low orbit satellites?

monitoring the weather

making scientific observations about unreachable places

have use in military

what can they also be used for?

what is complicated about this

can also be used for communication

however, because they travel so quickly, many satellites must work together to allow for constant coverage of a certain region