Define gravitational potential .

The work done per unit mass in bringing a test mass from infinity to a defined point in a gravitational field. It is represented by the symbol V and measured in J kg -1 .

Why is gravitational potential always negative near a planet?

Gravitational potential is defined as zero at infinity The gravitational force is attractive , so work must be done on a mass to move it away to infinity Therefore the potential at any finite point must be negative

Gravitational potential is negative on the surface of a planet and .......... with distance from the mass.

Gravitational potential is negative on the surface of a planet and increases with distance from the mass.

What two factors does the gravitational potential at a point depend on?

The mass of the object producing the gravitational field The distance of the point from that mass

True or False? Gravitational potential is measured in the same units as gravitational potential energy .

False. Gravitational potential energy is measured in joules (J), whereas gravitational potential is the potential energy per unit mass, measured in J kg -1 .

Define G as used in the gravitational potential equation.

Newton's gravitational constant , the constant of proportionality in the equation for gravitational potential.

True or False? Gravitational potential is a vector quantity, like gravitational field strength .

False. Gravitational potential is a scalar quantity; gravitational field strength is a vector quantity.

As a mass moves closer to a planet ( r decreases), its gravitational potential becomes ..........

As a mass moves closer to a planet ( r decreases), its gravitational potential becomes smaller (more negative)

What value of gravitational potential is defined at r = infinity?

Zero. Gravitational potential is defined as zero at an infinite distance from the mass.

When calculating r in the gravitational potential equation, where should the distance be measured from?

From the centre of the mass producing the field, not from its surface.

Should the negative sign be included when stating a change in gravitational potential (Δ V ), as opposed to the potential at a single point?

No. For a change in or difference in a value, only the magnitude is normally required. The negative sign is kept only when stating the potential at a point .

How can the change in gravitational potential Δ V be found from a graph of gravitational field strength g against distance r ?

By finding the area under the graph between the two distances, e.g. by counting squares or splitting the area into trapeziums.

On a graph of g against r , when the distance r doubles, g decreases by a factor of ..........

On a graph of g against r , when the distance r doubles, g decreases by a factor of four

True or False? On a graph of gravitational potential V against distance r , all values of V are positive.

False. All values of V are negative , so the graph is plotted below the r axis, since gravitational potential is always negative near a mass.

What relation does the graph of V against r follow as r increases?

A -1/r relation, a shallow increase in V , remaining negative throughout.

What relation does the graph of g against r follow as r increases?

A 1/r 2 (inverse square law) relation, a steep decline in g , remaining positive throughout.

Define a gravitational equipotential surface.

A surface (or line, in two dimensions) that joins together points which have the same gravitational potential.

When is work done on an object moving in a gravitational field?

When it moves against the gravitational field lines, i.e. away from the planet.

In a radial field, equipotential lines are .......... circles around the planet, which become further apart with distance.

In a radial field, equipotential lines are concentric circles around the planet, which become further apart with distance.

True or False? Equipotential lines are drawn with arrows to show the direction of the gravitational field, in the same way as field lines.

False. Equipotential lines have no arrows , since gravitational potential is a scalar quantity and equipotentials are not vectors.

What is true about the work done when an object moves along an equipotential surface?

No work is done , since Δ V = 0 along an equipotential surface or line.

In a uniform gravitational field, how are equipotential lines arranged?

Horizontal straight lines Parallel to each other Equally spaced

A LevelPhysicsAQAFlashcardsFields & Their ConsequencesGravitational Potential

Gravitational Potential (AQA A Level Physics): Flashcards

Exam code: 7408

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FrontGravitational Potential
Define gravitational potential.
FrontGravitational Potential
Why is gravitational potential always negative near a planet?
BackGravitational Potential
Gravitational potential is defined as zero at infinity
The gravitational force is attractive, so work must be done on a mass to move it away to infinity
Therefore the potential at any finite point must be negative

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Cards in this collection (29)

Define gravitational potential.
The work done per unit mass in bringing a test mass from infinity to a defined point in a gravitational field. It is represented by the symbol V and measured in J kg^-1.
What equation gives the gravitational potential energy (GPE) of an object close to the Earth's surface, and when is this equation valid?
$G P E = m g Δ h$
This equation is only valid for objects within/near the Earth's surface, where the gravitational field can be treated as uniform.
Why is gravitational potential always negative near a planet?
- Gravitational potential is defined as zero at infinity
- The gravitational force is attractive, so work must be done on a mass to move it away to infinity
- Therefore the potential at any finite point must be negative
Gravitational potential is negative on the surface of a planet and .......... with distance from the mass.
Gravitational potential is negative on the surface of a planet and increases with distance from the mass.
What two factors does the gravitational potential at a point depend on?
- The mass of the object producing the gravitational field
- The distance of the point from that mass
Define gravitational potential difference.
$Δ V = V_{f} - V_{i}$
Where V_f is the final gravitational potential and V_i is the initial gravitational potential (J kg^-1).
True or False?
Gravitational potential is measured in the same units as gravitational potential energy.
False.
Gravitational potential energy is measured in joules (J), whereas gravitational potential is the potential energy per unit mass, measured in J kg^-1.
Define G as used in the gravitational potential equation.
Newton's gravitational constant, the constant of proportionality in the equation for gravitational potential.
State the equation for gravitational potential V at a distance r from a mass M.
$V = - \frac{G M}{r}$
True or False?
Gravitational potential is a vector quantity, like gravitational field strength.
False.
Gravitational potential is a scalar quantity; gravitational field strength is a vector quantity.
As a mass moves closer to a planet (r decreases), its gravitational potential becomes ..........
As a mass moves closer to a planet (r decreases), its gravitational potential becomes smaller (more negative)
What value of gravitational potential is defined at r = infinity?
Zero. Gravitational potential is defined as zero at an infinite distance from the mass.
When calculating r in the gravitational potential equation, where should the distance be measured from?
From the centre of the mass producing the field, not from its surface.
Should the negative sign be included when stating a change in gravitational potential (ΔV), as opposed to the potential at a single point?
No. For a change in or difference in a value, only the magnitude is normally required. The negative sign is kept only when stating the potential at a point.
How can the gravitational field strength g at a point be found from a graph of gravitational potential V against distance r?
By drawing a tangent to the curve at that point and calculating its gradient. $g = - \frac{Δ V}{Δ r}$
How can the change in gravitational potential ΔV be found from a graph of gravitational field strength g against distance r?
By finding the area under the graph between the two distances, e.g. by counting squares or splitting the area into trapeziums.
On a graph of g against r, when the distance r doubles, g decreases by a factor of ..........
On a graph of g against r, when the distance r doubles, g decreases by a factor of four
True or False?
On a graph of gravitational potential V against distance r, all values of V are positive.
False.
All values of V are negative, so the graph is plotted below the r axis, since gravitational potential is always negative near a mass.
What relation does the graph of V against r follow as r increases?
A -1/r relation, a shallow increase in V, remaining negative throughout.
What relation does the graph of g against r follow as r increases?
A 1/r² (inverse square law) relation, a steep decline in g, remaining positive throughout.
What does the minus sign in $g = - \frac{Δ V}{Δ r}$ indicate?
The direction of the field, that it points towards the planet (towards lower potential).
Define a gravitational equipotential surface.
A surface (or line, in two dimensions) that joins together points which have the same gravitational potential.
State the equation for the work done ΔW when a mass m moves through a gravitational potential difference ΔV.
$Δ W = m Δ V$
When is work done on an object moving in a gravitational field?
When it moves against the gravitational field lines, i.e. away from the planet.
State the equation for the change in gravitational potential energy ΔGPE when a mass m moves between two distances r₁ and r₂ from a mass M.
$Δ G P E = G M m (\frac{1}{r_{1}} - \frac{1}{r_{2}})$
In a radial field, equipotential lines are .......... circles around the planet, which become further apart with distance.
In a radial field, equipotential lines are concentric circles around the planet, which become further apart with distance.
True or False?
Equipotential lines are drawn with arrows to show the direction of the gravitational field, in the same way as field lines.
False.
Equipotential lines have no arrows, since gravitational potential is a scalar quantity and equipotentials are not vectors.
What is true about the work done when an object moves along an equipotential surface?
No work is done, since ΔV = 0 along an equipotential surface or line.
In a uniform gravitational field, how are equipotential lines arranged?
- Horizontal straight lines
- Parallel to each other
- Equally spaced

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