5.4 Gravitational Flashcards
What causes gravitational fields
Objects having mass
How a spherical mass can be modelled
As a point mass
How do gravitational field lines work
They point in the direction that a mass would move and the closer together they are the stronger the field
Gravitational field strength
The force in newtons per unit mass
Equation for gravitational field strength in terms of forces (g=)
g=F/m
How are gravitational fields related to electric fields
They are both a form of a field giving rise to a force
What is the force between two masses proportional to
The product of the masses
The inverse square of the separation
Equation for gravitational field strength in terms of distance
g = -GM/r^2
Why do we not have to consider changing gravitational field strength when considering problems on earths surface
The change in distance is so small that the field can be considered uniform at the surface (this also applies to direction since we can consider the surface flat)
Relation between acceleration of free fall and gravitational field strength
They have the same numerical value (9.81) but are different things with different units
Keplers first law
Planets move around the Sun in an ellipse, with the Sun at one focus of the ellipse
Keplers second law
A line joining the Sun to a planet will sweep out equal areas in equal times
Keplers third law
T^2 ∝ r^3
where T is the period and r is the mean distance
How centripetal force relates to gravity
The centripetal force on a planet is provided by the gravitational force between it and the Sun
How to derive the constant for keplers third law
Equation centripetal force to the gravitational force