Studied by 0 peopleDescribe gravity
attraction between two objects with mass, universal attractive force, weak force, infinite range
What is a field?
a region where an object experiences a force
What are gravitational field lines?
represent a gravitational field
What happen as the distance from the centre of mass of the object increases?
the gravitational field strength decreases
What are the rules for gravitational field lines?
straight, pointing to centre of mass (in direction of force), the density of field lines represents gravitational field strength, the lines never cross, can be modelled as uniform
What does it mean when a gravitational field is modelled as uniform?
gravitational field is drawn as parallel lines at equal intervals towards surface
What is an example of a gravitational field modelled as uniform?
surface of a planet on small scale
How is gravitational field strength is modelled close to the surface of the Earth?
as uniform
What is the numerical value of gravitational field strength close to the surface of the Earth?
the acceleration of free fall, g, 9.81
What is gravitational field strength?
the gravitational force experienced per unit mass by an object at that point in a gravitational field
Why do objects experience a gravitational field?
due to the objects having mass
How are objects with mass modelled?
as a point mass, where the point is the centre of the mass of the object
What is Newton’s 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 their separation
Why is gravitational force negative?
it is an attractive force
What is the equation for gravitational field strength?
g=-GM/r2
What is Kepler’s first law?
the orbit of a planet is an ellipse, with the sun at one focus
What is Kepler’s second law?
a line segment joining a planet and the sun sweeps out equal areas during intervals of equal time
What is Kepler’s third law?
the square of the orbital period T is proportional to the cube of the average distance r from the sun
What is centripetal force on a planet?
gravitational force between it and the sun
What is centripetal force?
the net force acting towards the centre of the circle
What is the equation for the orbital period of a geostationary satellite?
T2=4pi2r3/GM
What is the derivation of T2=4pi2r3/GM?
centripetal force=gravitational force so GmM/r2 = mv2/r, then v2=GM/r and v=2pir/T so sub it back in to get the final equation
What are satellites?
objects that orbit other larger objects
What is the period of a geostationary satellite?
one day
What are the uses of geostationary satellites?
always above the same point on Earth’s surface, so useful for communications and surveying as they provide continuous coverage
What is gravitational potential?
work done per unit mass to move an object to that point from infinity
What are the units of gravitational potential?
Jkg-1
What does a force-distance graph look like for a spherical mass?
What does a force-distance graph look like for a point mass?
What is area under a force-distance graph?
work done
How can an object escape a gravitational field?
kinetic energy is equal to or greater than gravitational potential energy
What is escape velocity?
minimum velocity required to escape a gravitational field
Note
Flashcard