A force field is a region of space in which a specific type of object experiences a force .

What property must an object have to experience a gravitational force?

Any object with mass experiences a gravitational force.

What do gravitational field lines show?

The direction of the gravitational force (and therefore the acceleration ) that would act on a mass placed at that position in the field.

In which direction do gravitational field lines always point, and why?

Towards the centre of mass of a body, because the gravitational force is always attractive .

For a point outside a uniform sphere, the mass of the sphere may be treated as a .......... located at its centre.

For a point outside a uniform sphere, the mass of the sphere may be treated as a point mass located at its centre.

When can an object be treated as a point mass?

When it covers a distance that is very large compared to its own size (dimensions), so its dimensions can be neglected.

True or False? The gravitational field lines around a uniform sphere are different from those around a point mass.

False. They are identical to those around a point mass, because a uniform sphere's mass is evenly distributed.

Define gravitational field lines .

Lines that represent the direction of the gravitational force (and acceleration) on a test mass placed in the field.

What shape do gravitational field lines take around a point mass?

They are radially inward , pointing towards the point mass.

How are gravitational field lines represented in a uniform field?

As equally spaced, parallel lines.

What does the spacing (density) of gravitational field lines indicate?

The magnitude of the field — the closer together the lines, the stronger the field.

Radial fields, where the field strength changes with distance from the centre, are classed as .......... fields.

Radial fields, where the field strength changes with distance from the centre, are classed as non-uniform fields.

True or False? In a uniform gravitational field, the field strength g varies from point to point.

False. In a uniform field, g is constant at every point.

What are the units of gravitational field strength?

N kg -1 (equivalent to m s -2 ).

What two factors affect the gravitational field strength at the surface of a planet?

The planet's radius (or diameter) and its mass (or density).

How does g vary with r inside a uniform planet ( r R )?

Inside, g is directly proportional to r ; outside, g is inversely proportional to r 2 .

Near the Earth's surface, the gravitational field is uniform, so the gravitational field strength is .......... at every point.

Near the Earth's surface, the gravitational field is uniform, so the gravitational field strength is constant at every point.

True or False? Gravitational field strength is always constant everywhere in space, equal to 9.81 N kg -1 .

False. It is only constant close to the Earth's surface, where the field is uniform . Further away, it decreases with a 1/r 2 relationship.

Define Newton's Law of Gravitation .

The gravitational force between two masses is proportional to the product of their masses and inversely proportional to the square of their separation r .

If the distance between two masses doubles, by what factor does the gravitational force between them change?

It decreases by a factor of four (inverse square law).

What does the negative sign in Newton's Law of Gravitation indicate?

That the gravitational force is attractive .

In Newton's Law of Gravitation, the distance r is measured between the .......... of the two masses, not their surfaces.

In Newton's Law of Gravitation, the distance r is measured between the centres of the two masses, not their surfaces.

True or False? When calculating r for a satellite orbiting a planet, r is equal to the satellite's altitude above the surface.

False. r must include the planet's radius added to the altitude, since r is measured from centre to centre.

A LevelPhysicsOCRFlashcards5. Newtonian World & AstrophysicsGravitational Fields

Gravitational Fields (OCR A Level Physics): Flashcards

Exam code: H556

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FrontGravitational Fields
Define force field.

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Cards in this collection (26)

Define force field.
A force field is a region of space in which a specific type of object experiences a force.
What property must an object have to experience a gravitational force?
Any object with mass experiences a gravitational force.
What do gravitational field lines show?
The direction of the gravitational force (and therefore the acceleration) that would act on a mass placed at that position in the field.
In which direction do gravitational field lines always point, and why?
Towards the centre of mass of a body, because the gravitational force is always attractive.
For a point outside a uniform sphere, the mass of the sphere may be treated as a .......... located at its centre.
For a point outside a uniform sphere, the mass of the sphere may be treated as a point mass located at its centre.
When can an object be treated as a point mass?
When it covers a distance that is very large compared to its own size (dimensions), so its dimensions can be neglected.
True or False?
The gravitational field lines around a uniform sphere are different from those around a point mass.
False.
They are identical to those around a point mass, because a uniform sphere's mass is evenly distributed.
Define gravitational field lines.
Lines that represent the direction of the gravitational force (and acceleration) on a test mass placed in the field.
What shape do gravitational field lines take around a point mass?
They are radially inward, pointing towards the point mass.
How are gravitational field lines represented in a uniform field?
As equally spaced, parallel lines.
What does the spacing (density) of gravitational field lines indicate?
The magnitude of the field — the closer together the lines, the stronger the field.
Radial fields, where the field strength changes with distance from the centre, are classed as .......... fields.
Radial fields, where the field strength changes with distance from the centre, are classed as non-uniform fields.
True or False?
In a uniform gravitational field, the field strength g varies from point to point.
False.
In a uniform field, g is constant at every point.
Define gravitational field strength g.
The force per unit mass experienced by an object at that point in a gravitational field: $g = \frac{F}{m}$
What are the units of gravitational field strength?
N kg^-1 (equivalent to m s^-2).
What two factors affect the gravitational field strength at the surface of a planet?
The planet's radius (or diameter) and its mass (or density).
State the equation for gravitational field strength g in a radial field due to mass M.
$g = - \frac{G M}{r^{2}}$
The negative sign shows that the field is attractive.
How does g vary with r inside a uniform planet (r < R) compared to outside it (r > R)?
Inside, g is directly proportional to r; outside, g is inversely proportional to r².
Near the Earth's surface, the gravitational field is uniform, so the gravitational field strength is .......... at every point.
Near the Earth's surface, the gravitational field is uniform, so the gravitational field strength is constant at every point.
True or False?
Gravitational field strength is always constant everywhere in space, equal to 9.81 N kg^-1.
False.
It is only constant close to the Earth's surface, where the field is uniform. Further away, it decreases with a 1/r² relationship.
Define Newton's Law of Gravitation.
The gravitational force between two masses is proportional to the product of their masses and inversely proportional to the square of their separation r.
State the equation for Newton's Law of Gravitation.
$F = - \frac{G m_{1} m_{2}}{r^{2}}$
If the distance between two masses doubles, by what factor does the gravitational force between them change?
It decreases by a factor of four (inverse square law).
What does the negative sign in Newton's Law of Gravitation indicate?
That the gravitational force is attractive.
In Newton's Law of Gravitation, the distance r is measured between the .......... of the two masses, not their surfaces.
In Newton's Law of Gravitation, the distance r is measured between the centres of the two masses, not their surfaces.
True or False?
When calculating r for a satellite orbiting a planet, r is equal to the satellite's altitude above the surface.
False.
r must include the planet's radius added to the altitude, since r is measured from centre to centre.

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