Gravitation Flashcards
Define Newtons law of Gravitation
The force of attraction between two point masses is proportional to the product of the two masses and are inversely proportional to the square of the distance between them
Define the gravitational potential at a point in a gravitational field
Gravitational potential at a point, is defined as the energy required to move a unit mass from infinity to that point
Define escape velocity
The minimum velocity an object must have at the surface of a planet to escape the pull of gravity, using its own kinetic energy.
What is the units of gravitational potential
Jkg^-1
What is the units of G (Gravitational Constant)
NM^2kg^-2
What is a gravitational field
A region in space in which a massive object experiences a gravitational force
What are the units for gravitational field strength
Nkg^-1
How does an object lose potential energy when at infinity
An object has no joules of energy when it has been moved an infinite distance from the planet
An object that moves from this point of infinity, back to the planet loses potential energy
Define gravitational field strength
Force per unit mass that the field strength has at that point
What is the unit for gravitational force
Newtons
What are the advantages of a geo-synchronous orbital satellite
maintains a fixed position relative to surface of Earth (1)
period is 24 hrs (1 day) or same as for Earth’s rotation (1)
offers uninterrupted communication between transmitter and receiver (
Define gravitational potential
Gravitational potential is the potential energy per kilogram at a point in a field.
What is fundamental about gravitational fields
- Always attractive
Why do rockets not need to have an escape velocity for Earth to reach orbit?
-They are not going to infinity, just escaping a gravitational field
- Does not rely on kinetic energy, relies on chemical
energy produced by thrusters
Define coulombs law
The force between two charges is proportional to the product of the charges and proportional to 1 over the square of the distance between them
Is an Electric field a vector or scalar quantity
vector - it has both magnitude and direction
Explain the path of a charge in a electrical field
The path is a parabola. As the electron is negatively charged, it experiences a constant acceleration upwards due to the horizontal field. Its horizontal velocity remains constant but its vertical velocity is constantly changing
Define absolute electric potential
The potential difference between a point and a point at zero potential, which is infinitely far away
Define potential difference
The work done against an electric field, in moving unit charge from one point to a second point at a higher potential. If charge moves from a point of higher potential to lower potential work is done by the electric field.
If a charge is negative, explain how it would reach infinity
In this case, the charge is negative, work must be done against the field in order to reach infinity. Therefore the charge gains Ep as it moves to infinity. This is because at infinity the potential energy is zero. So the potential in the field must be negative.
What is fundamental about an electric field
Always positive, regardless of position
What is the units for electric field strength
Vm^-1
Why is gravitational potential always negative
- At infinity, gravitational potential is zero
- This means the potential near to any planet is a
negative quantity, because potential energy decreases
as something falls towards the planet
What is the equation for gravitational potential energy
Ep = ∆V x m
Electric potential at a point
electric potential at a point is defined as the amount of work done in moving a unit positive charge from infinity to that point.
Field
area of space where mass/charge experience a force
field lines
show the direction of the force on a point mass/positive test charge
What is the K constant for the electric field equation
K= 9x10^9
Field strength
How much force something would feel
Definition of potential
Energy needed to move 1kg of mass or 1 coulomb of charge to move from infinity to that point
