4.2.2 Gravitational Fields

Question 1

What is a gravitational field?

Answer 1

It is a region of space in which a mass experiences a force due to the presence of another mass.

Question 2

How do radical field lines act with gravity?

Answer 2

They are always attractive for gravity.

Question 3

How does a uniform field effect gravitational fields? (mention surface and how it varies)

Answer 3

The field is radical to the planet but over a small distance it is uniform.
Distance is small compared to surface.

Question 4

What is gravitational field strength?

Answer 4

The force experienced per unit mass by a mass placed in the field.

g = F/m

units: Nkg-1 or ms-2

Question 5

How can gravitational field strength be defined from field diagrams?

Answer 5

Direction of field indicated by arrows and magnitude of field shown by density of field lines.

Question 6

How does point mass help calculating the grav field strength?

Answer 6

Consider the planet a point mass.

Question 7

How is the grav field strength affected by variations in M and r?

Answer 7

As the mass increases, g is proportional to M.
As distance from mass increases g decreases, g is inversely proportional to r squared.
Another example of inverse square law.

Question 8

What is the equation for g in a radical field?

Answer 8

g = GM/r squared

Question 9

What do the letters stand for?

Answer 9

g = grav field strength
G = universal constant of gravitation
M = mass
r = radical distance assuming its at point mass.

Question 10

What is a gravitational force and how does it relate to Newton’s Law of Gravitation?

Answer 10

Gravitational force is directly proportional to the product of the masses and inversely proportional to the square of the distance between them.

Question 11

What do the letters mean in Newton’s equation?

Answer 11

F = gravitational force
G = universal constant of gravitation
M1 = larger mass
M2 = smaller mass
r squared = distance between masses

Question 12

What is gravitational potential energy (PE)?

Answer 12

GPE is work done bringing a mass from infinity to that point in the gravitational field. As the gravitational field is always attractive the work done is negative and the grav potential is always negative.

PE = - GMm/r

Question 13

Is gravitational potential energy a scalar or a vector?

Answer 13

It is a scalar quantity

Question 14

What is gravitational potential?

Answer 14

It is the work done in bringing a unit mass from infinity to that point in the field.

Vg is the work per unit mass to bring a mass from infinity.

Vg = PE/m

Question 15

What are equipotentials in a radical field?

Answer 15

An equipotential surface links all points at the same potential.

E.g for a point mass it would the surface of a sphere where all points would have an equal distance from the point charge.

Question 16

Is there any work done when a mass moves onto the equipotential surface?

Answer 16

No work would be done when a test mass moves on this equipotential surface, from one position to another so there would be no energy change.

Question 17

Potential Gradient

Answer 17

The steepness of the surface represents the strength of the gravity field g.

The magnitude of the field strength at any point is equal to the potential gradient.

Question 18

What is the definition of escape velocity?

Answer 18

It id the minimum velocity an object must have to escape the gravitational field and reach zero velocity at infinity.