Gravitational fields Flashcards
how do you find the acceleration due to gravity
measure mass
measure reading on newtonmeter
f=ma
graph should intercept origin
force on y mass on x gradient should be acceleration
what is the value for G
G = 6.67 x10^-11 m^3kg^-1s^-2
when would you not uses Egp = Ke
When there is a big change of height due to the effect of gravity is different the further away you are
whats the Force (w) equation
Fw = - Gmamb
————-
r^2
equation for effect due to gravity
follows the inverse square law
g=Gm
——
r^2
Definition for Gravitational Potential
**The gravitational potential energy (G.P.E) is the potential energy an object has when lifted off the ground **
V is the GPE per unit mass in a gravitational field
V = Egp
——
m
Therefore the Gravitaional potential at a position in a field caused by mass B would be
Vb = - Gmb
———
r
simplified potential equation
V = - Gm
——–
r
What equation relates Gravitational Potential and velocity
V1 - V2 = 1/2 x v^2
simularities of gravitational fields and electric fields
- both fields follow the inverse square law
( inversely proportional to the square distance away(r))
2.both can be radial and uniform fields - both have infinite range
Differences of Gravitational fields and electrical fields
1.Gravitational fields only cause attraction where as electric fields both attract and repel
2.gravitational fields only act on objects with mass where as electric fields only act on charged particles
3.Gravitational potential is always negative where as electric potential can be either positive or negative
4. the force between charges at a given separation is much stronger than the force between masses at the same separation
what is keplers Third Law
The square of an orbiterd period, T, is proportional to the cube of its seperation from what is orbiting , r.
It is also stated that the square of the period, T, is inversely proportional to the mass being orbited
equations for centripetal forces
f = mv^2
——-
r
f = gmamb
———-
r^2
velocity in terms of mass
Gm
—— = v^2
r
state the defining equation for newtons law of gravitation
F = - GM
/ ———
r^2
what does newtons law of gravitation state mean
The gravitational force between two masses is proportional to the product of their masses and is inversely proportional to the square of the seperation of their centres
what is gravitational field strength? and the unit
the force per unit mass felt by the object
Nkg^-1
what is gravitational potential at a point?
The energy transferred per unit mass when moving an object from infinity to that point
state the equation for gravitational potential
V = -GM
——–
r
what is an equipotential
a plane in which all points have the same potential
what is true when a mass moves along an equipotential
no work is done when moving along an equipotential
what does the area under a force-seperation graph represent
energy
what do field lines tell you
the direction of the arrows show the direction of the field. the strength of the field is represented by the density of the field lines
what is gravitational potential
the potential energy per unit mass, at any point in the field. Zero potential is defined at infinity, hence at a point close to a mass toe potential of an object would be negative
work done by moving a mass in a field
work done = mass x change in gravitational potential
what is gravitational potential difference
Gravitational potential difference is the difference in the gravitational potentials of two points in a gravitational field
how much work is done per unit distance when you move along an equipotential ?
No work is done when moving across equipotentials, as the potential at each point is the same
why is gravitational potential a negative value?
work needs to be done to move an object from the inside the field to outside the field. since outside the fields potential is defined as zero then the potential inside the field must be negative
how is the orbital period related to the radius of a circular orbit
T^2 is proportional R^3
compare the Potential energy and Kinetic energy of a lower orbit and a higher orbit
A lower orbit (smaller m) has less potential energy and more kinetic energy than a higher orbit (bigger r)
what type of matter is affected by a gravitational field?
Any object or matter with mass will experience an attractive force.
what is the relationship between the field strength and the field lines that represent it ?
the closer the lines are together, the stronger the gravitational field strength. The further apart the lines are, the weaker the field strength.
what is a point mass?
A point mass is a theoretical object that has a mass but no dimensions. This means that all of its mass acts at a single point
what is the cheat equation for the velocity using gravitational potential
V1 - V2 = 1/2 x v^2
-Gmb -Gmb
——— - ——– =1/2 v^2
r1 r2
