Gravitational Fields Flashcards
(14 cards)
What is a force field?
An area in which an object experiences a non-contact force
What is a gravitational field?
A region where a mass experiences a force due to gravity
What can gravitational fields be visualised with?
By vectors, known as field lines
Field lines always point towards the centre of the mass producing the field since gravitational forces are attractive
Field lines show the direction if the gravitational force that would be exerted on a mass placed at a position in that field
In other words, they show the direction of which the mass would be accelerated
Field lines are closer together at points where the field is stronger
What is gravitational field stength?
The attractive gravitational force that a unit mass would experience at a given point in a gravitational field
In other words, it is the acceleration due to the gravitational field
Defined by the equation:
g = F/m for a uniform field
What does the gravitational field strength equation show?
That the larger the mass of an object, the greater its pull on another mass
What is the gravitational field strength at the surface of the Earth?
9.81 Nkg-1
What is Newton’s Law of Universal Gravitation?
Describes the force of gravitational attraction between two masses
F = Gm1m2/r2
Where r is the distance between the centre of the two masses
What is the Inverse Square Law (in context of Newton’s Law of Universal Gravitation)?
The 1/r2 is the inverse square law
This means that as the distance between the two masses doubles, r becomes 2r
∴ 1/r2 becomes 1/4r2
Hence the gravitational force between the two masses reduces by a factor of 4
What is the derivation for the equation of the gravitational field due to a point mass?
g = F/m1
F = gm1
F = Gm1m2/r2
∴ gm1 = Gm1m2/r2
∴ g = Gm2/r2
What is gravitational potential in a radial field?
The work done per unit mass to move a mass from infinity to a defined point within a gravitational field
Where infinity is the point at which gravitational potential is 0
Given by the equation:
** V = - Gm/r**
Why is the value of the gravitational potential always negative?
Since gravitational fields are attractive, the work must be done against the force of gravity to move the mass away from the source of the field
What is an equipotential?
A plane of points with equal gravitational potential
This means that the work done travelling on an equipotential is 0
What are the similarities between gravitational and electric fields?
The magnitude of the gravitational force between two point masses and the electrostatic force between two point charges follow the inverse square law
The field lines around spherical masses and spherical charges are radial
The field lines in a uniform gravitational and electric field are parallel and equally spaced
The gravitational field strength and electric field strength both have a 1/r2 relationship in a radial field
The gravitational potential and electric potential both have a 1/r relationship
What are the differences between gravitational and electric fields?
In gravitational fields, the force exerted is always attractive, while in electric fields, it can be either repulsive or attractive
Gravitational forces act on particles with mass whilst electrostatic forces act on particles with charge
Gravitational potential is always negative whilst electric potential can be negative or positive
Objects cannot be shielded from the force exerted by gravitational fields but can be shielded from the force exerted by electric fields
