9702 · 13.1
Gravitational field flashcards
Revision flashcards for Cambridge 9702 Gravitational field (syllabus 13.1). Flip, recall, then mark a real past-paper question.
Card
How is gravitational field strength (g) defined?
The gravitational force acting per unit mass at a given point.
Card
What two factors does Newton's Law of Gravitation state the attractive force depends on?
Directly proportional to the product of the masses; inversely proportional to the square of the distance between their centres.
Card
Why is gravitational potential considered negative?
Because work is done *by* the field (energy is released) when a mass moves from infinity (where potential is zero) into the field.
Card
What do closer gravitational field lines indicate about the field?
They indicate a stronger gravitational field in that region.
Card
For calculations involving objects *outside* a uniform sphere, how can its mass be considered?
As if it's concentrated entirely at its centre, acting as a point mass.
Card
What is the universal gravitational constant G?
A fundamental constant ($6.67 \times 10^{-11} \text{ N m}^2 \text{ kg}^{-2}$) that quantifies the strength of the gravitational force.
Card
What does gravitational field strength (g) also represent?
The acceleration an object would experience if allowed to fall freely in that field.
Card
What is gravitational potential ($\phi$)?
The work done per unit mass to bring a unit mass from infinity to a specific point in the field.
Card
What is the conventional value for gravitational potential at an infinite distance from a mass?
Zero.
Card
How does gravitational field strength vary with distance in a radial field?
It follows an inverse square law (g \propto 1/r^2).
Card
What is the formula for gravitational potential ($\phi$) at a distance r from a mass M?
$\phi = -\frac{GM}{r}$
Card
How does the graph of gravitational field strength (g) against distance (r) from a point mass look?
It's a curve in the first quadrant, starting high and decreasing rapidly towards zero, following an inverse square law ($g \propto 1/r^2$). It is always positive.
Card
How does the graph of gravitational potential ($\phi$) against distance (r) look?
It's a curve in the fourth quadrant (negative values), starting at its most negative value and increasing towards zero as r increases, following an inverse law ($\phi \propto -1/r$).
Card
What is the relationship between gravitational field strength (g) and the gradient of the gravitational potential ($\phi$) graph?
The field strength is the negative of the potential gradient: $g = -\frac{d\phi}{dr}$.