21 Gravitational Fields Flashcards
Gravitational potential energy Ep
At a point in a gravitational field is the work done to move a small object from infinity to that point. The change of gradational potential energy of a mass (m) moved through a height (h) near the Earths surface ΔEp = mgΔh
Gravitational potential v
At a point in a gravitational field is the work done per unit mass to move a small object from infinity to the point. At the distance r from the centre of a spherical object of mass (M).
V= -GM/r
(a point is the work done per unit mass to move a small object from infinity to that point)
zero value at infinity
Equipotential
A line or surface in the field along which the electric or gravitational potential is constant
(no work is done when moving along a equipotential surfaces )
Gravitational fields strength, g
Force per unit mass on a small mass placed in the field
g = F/m ( gravitational force on a small mass)
Distance r from a point mass (M).
g= GM/r^2
radial field
a field in which the field lines are straight and converge or diverge as if from a single point
field line (line of force)
direction of a field line indicates the direction of the force. an electric field line is the path followed by a free positive test charge. the gravitational field line of a single mass point towards that mass
uniform gravitational field
The earth is uniform over a region which is small compared to the scale of the Earth
potential gradient
at a point in a field is the change of potential per unit charge of distance along a field line at that point.
potential gradient = - the field strength at any point
keeper’s third law
for any planet, the cube of its mean radius of orbit is directly proportional to the square of its time period
R^3 / T^2 = GM/ 4(pi)^2
newton’s law of gravitation
the gravitational force F between two point masses M and m at distance r apart
F= GMm/ r^2
escape velocity
the minimum velocity an object must be given to escape. from the planet when projected vertically from the surface
gravitational field (g) a vector?
yes its a vector
Gravitational Force is a ______ force
attractive force
Gravitational fields
a region within which an object experience gravitational force
the closer the lines the stronger the field
field strength decreases as the distance from the object increases
g= F/M
r is measured from the ____
centre
Orbital speed
inversely proportional to the square root of the orbital radius
(so Jupiter travels slower than earth)
centripetal force of an orbit
GMm/r^2 = mv^2 /r
V^2 = GM /r
one complete orbit (equation)
T = 2(pi)r / v
use the equation V^2 = GM /r
T^2 = 4(pi)^2r^3 / GM
geosynchronous orbit
has the same orbit time as the earth (24 hours)
appears stationary when your on earth
Rocket launch
engine provides a constant force which mean the rocket can go slower because the engine would continue to give you thrust to overcome the gravitational potential energy
from what height is the gradational force not 9.81 the right value?
100m
Cavendish experiment
a acute measurement of G (6.67 *10-11)
escape velocity equation
V^2 = 2gR
Satnav
uses synchronised and measure the time difference between the signals form the satellites
energy of an orbiting satellite
E= -GMm / 2r E= EP+EK
the negative sign in the equation means
gravity is a attractive force
we treat all objects as
point masses
gravity field are radical meaning they come together to a
straight line
the pull being directly towards the centre, the closer in you get the stronger the pull
gravity
universal attractive force acting between all matter
work done in moving mass
W = mV
area under graph of g against r
V
