Graitational Fields Flashcards
Define gravitational field strength
The gravitational force experienced by an object per unit mass within the force field.
What are gravitational field lines
Lines which demonstrate the strength and direction of force of a force field. The closer the lines, the stronger the force. Separation between lines as distance increases from earth indicates weaker force as distance increases. Uniform gravitational field is indicated by parallel lines at equal distance between each other.
Newtons law of gravitation
Two objects with masses M and m create gravitational fields, resulting in forces between them. Newton’s third law states the forces are equal in magnitude but opposite in direction.
How to find force if there are Multiple objects
Resultant force determined through vector addition. If in 2 dimensions, use Pythagoras or sin or cosine rule.
What can we observe from the gravitational field strength in a radial field
The gravitational field strength is directly proportional to the mass of the object creating the field (g ∝ M).
The gravitational field strength is inversely proportional to the square of the distance from the center of mass
(g ∝ 1/r^2).
What is an ellipse
An elongated circle
What is the foci of an ellipse
2 points that lie on the ellipses major radius, whose sum of distances from foci to any point on the circumference on an ellipse is constant.
What is Keplers First law
The orbit of a planet is elliptical with the sun at one of the 2 foci
What is Keplers Second Law
A line segment joining a planet and the sun sweeps out equal areas during equal intervals of time.
What is Keplers Third Law
The square of the orbital period T of a planet is directly proportional to the cube of its average distance r from the Sun.
What is one astronomical unit (AU)
1.5 x 10^11
Derive the equation for Keplers 3rd Law
Orbit of planet around sun can be modelled as circular motion, as orbit is almost circle. Centripetal force on planet= Gravitational force on planet. Make v^2 the subject. v is equal to 2pi*radius over Time period. Square this and make equal to rearranged formula. Rearrange to make T^2 subject.
Geo stationary sateliites
A satellite placed in orbit above the earths equator, rotates in the same direction as earth and has an orbital period of 24 hours. Always at same point above earth.
What is gravitational potential, V lil g
Work done per unit mass to move an object to that point from infinity. Scalar quantity. Max at infinity (0 joules), negative closer to Gravity creator.
What is gravitational potential energy
Work done to move the mass
from infinity to a point in a gravitational field. E = mV
