D1 Gravitational Fields Flashcards
What is a gravitational field?
A region of space surrounding a body in which another body experiences a gravitational force due to their masses.
Gravitational force formula
F = GMm/r2
How are the field lines directed in a gravitational field near the Earth’s surface?
Parallel and equally spaced.
How are field lines directed over large distances from the Earth’s surface
Radially towards the earth’s centre
Weakens with distance
What does Newton’s law of gravitation state?
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.
What is the nature of the forces described by Newton’s universal law of gravitation?
Always attractive.
What is gravitational field strength (g)?
The gravitational force exerted per unit mass on a small mass placed at that point.
Gravitational field strength formula
g = F/m = GM/r2
In a gravitational field, what is the relationship of gravitational field strength (g) inside the Earth?
g is directly proportional to distance r from the center.
What is Kepler’s First Law?
Planetary orbits are elliptical with a star (the Sun) at a focus.
What does Kepler’s Second Law state?
The radius vector from the star (the Sun) to the orbiting body sweeps equal areas in equal times.
What is Kepler’s Third Law
GMm/r2 = mRw2 (okay actually it’s the relationship between period and radius but I want to remember this so)
What is the gravitational potential energy (Ep) of a point mass in a gravitational field?
The work done by an external agent in bringing the point mass from infinity to that point.
What does the negative sign in gravitational potential energy (Ep) indicate?
It means that Ep is always negative and has values less than zero.
What is escape velocity?
The minimum speed an object must have at the start to just escape from the gravitational influence of a body.
Formula for escape velocity
v esc = √(2GM/r)
Fill in the blank: The gravitational force acting on each of two masses is ______ and ______.
equal and opposite (By Newton’s 3rd Law)
By Kepler’s Third Law, what is the relationship between T and R
T (period of rotation); R (radius of orbit)
T squared is directly proportional to R cubed
What is the significance of the neutral point in the interaction of two gravitational fields?
Gravitational field strength (g) is zero (but not potential)
Gravitational force due to each of two masses on a small mass placed at that point is equal to
Fill in the blank: Neutral point is always closer to the _ mass
smaller
What happens to gravitational potential energy as a point mass is moved toward infinity?
Ep approaches zero.
Gravitational potential energy formula
Ep = -G(Mm/r).
Gravitational potential formula
Vg = -Gm/r
What is the total energy of a body in an orbit?
Total mechanical energy = KE + PE
