7.2 - Gravitational Potential Flashcards
What is gravitational potential energy?
The energy an object possesses due to its position in a gravitational field.
What is gravitational potential?
The work done per unit mass in bringing a test mass from infinity to a defined point.
What does it mean when we are observing a mass from infinity?
Observed from infinity = don’t take into account the mass of the planet we are observing from.
What is the gravitational potential symbol and units?
V, measured in J/kg
Why is gravitational potential always a negative value?
It is defined as zero at infinity.
Since gravitational force is always attractive, work must be done on a mass to reach infinity.
(so V is increasing the further away from the centre of mass)
Does gravitational potential increase or decrease when moving closer to a large body?
Decrease.
What is the equation for gravitational potential?
V = GM/r
M = mass of body producing the g field
r = distance from the centre of the mass to the point mass
Is gravitational potential a scalar or vector?
Scalar, the negative sign isn’t a direction
What is the difference between gravitational field strength and gravitational potential?
g - the force per unit mass on an object in a gravitational field
V - the work done per unit mass in bringing s test mass from from infinity to a specific point in the g field.
What is the equation that shows the relation of g, V and r?
g = - ΔV/Δr
g = grav field strength (N/kg)
ΔV = change in grav potential (K/kg)
Δr = distance from the centre of a point mass (m)
What does the relationship of V against r look like graphically?
a -1/r reciprocal graph
What are 4 key features of a V against r graph?
- value for V always negative
- -1/r
- the gradient at any point on graph is g at that point
- the graph has a shallow increase as r increases
What does the graph of g against r look like?
A 1/r² relationship.
What are 4 key features of a g against r graph?
- value of g always positive
- 1/r² = inverse square law relation
- Area under graph is ΔV
- graph has a steep decline as r increases
What is the equation for work done in moving a mass?
ΔW = mΔV
ΔW = change in work done (J)
m = mass (kg)
ΔV = change in grav potential (J/kg)