Section 7 Chapter 21: Gravitational fields Flashcards
If a small mass is placed near a massive body, how do they interact?
They attract to each other with equal and opposite forces.
The body may be big enough where this force will create no noticeable movement, but the small mass is pulled towards the body
What is a field line / line of force?
The path which a smaller mass follows when it is pulled to a more massive object
What are the units for gravitational field strength?
Nkg⁻¹
it is only ms⁻² when it is the acceleration of free fall
Prove the acceleration of an object under free fall in a gravitational field = g
g = F / m
F = ma
g = ma / m
g = a
Describe a radial field
Field lines are directed to the centre of the body
The magnitude of g in a radial field decreases with increasing distance from the massive body
Uniform and radial field patterns
https://imgur.com/VUauv0e
Describe a uniform field
Gravitational field strength is the same in magnitude and direction throughout the field.
The field lines are parallel to each other and equally spaced
Uniform and radial field patterns
https://imgur.com/VUauv0e
What is the range of gravity?
Infinite. However, at far enough distances, the attraction of gravity become negligible
What is gravitational potential energy?
Energy of an object due to it’s position in a gravitational field
What is gravitational potential at a point in a gravitational field?
Work done per unit mass to move a small object from infinity (where GPE is 0) to that point
What is the unit of gravitational potential?
Jkg⁻¹
Generally, if a small object is moved from gravitational potential V₁ to gravitational potential V₂ what is it’s change in GPE?
ΔEₚ = m(V₂ - V₁) = mΔv
ΔW = ΔEₚ
ΔW = mΔv
V = W/m
What is an equipotential?
Surfaces of constant potential
No work needs to be done to move along an equipotential surface
What equipotentials look like near a planet
https://imgur.com/hCbslSu
Why are equipotentials for equal increases in potential spaced further apart when moving away from earth’s surface?
Further from earth = Weaker gravitational field = Gain in GPE per metre of height lower
= Equal increases in potential is further apart
What equipotentials look like near a planet
https://imgur.com/hCbslSu
Why are equipotentials equal near the surface over a small region?
Gravitational field over a small field is uniform
What is a potential gradient in a gravitational field?
???
Change of potential per metre at that point
What is the trend in potential gradient as you move away from earth’s surface?
It decreases. You gain less potential per metre of height gained as the field becomes weaker
What is Kepler’s first law?
What is Kepler’s second law?
What is Kepler’s third law?
T² ∝ R³
T² / R³ = k
