gravitational fields Flashcards
what is gravity
universal attractive force that acts between all matter
what are field lines due to
objects having mass
what do gravitational field lines represent
the direction of a field and the strength of the field depending on the density of field lines
what is gravitational field strength
force per unit mass
g = f/m
where is the mass concentrated
in the centre
what happens to field lines close to the surface of the earth
they are uniform, equally spaced and almost parallel
equation for gravitational force
g = -GmM/r^2
what is g
g is the force per unit area in a uniform gravitational field
how to derive g = GM/r^2
use
F = -GMm/r^2, g = f/m
newtons law of gravitation
two point masses attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them
keplers first law
orbit of a planet is an ellipse with the sun at one focus
keplers second law
line segment joining a planet and the sun sweeps out equal areas during intervals of equal time
keplers third law
the square of the orbital period T is proportional to the cube of the average distance r from the sun, this can be proved by considering the forces acting on the planet
derive keplers third law
use GMm/r^2 and mv^2/r
what are geostationary orbit
- orbital period of 24 hours, same direction of rotation as earth
- equatorial orbit
- remain fixed in sky to observer
gravitational potential
the potential energy per kilogram at any point in the field, 0 potential is defined at infinity so at a point close to a mass the potential of an object would be negative
gravitational potential difference
the difference in the gravitational potentials of two points in a gravitational field
what kind of law is newtons law of gravitation
inverse square law
what is meant by an inverse square law
one quantity is inversely proportional to the square of the other
what tis the gravitational potential energy at a point in the field
the work done per unit mass in moving an object from infinity to that point in the field
escape velocity
the min velocity an object requires in order to escape the gravitational field of an. object when projected vertically from its surface
