Gravitational Fields Flashcards
What objects experience a greater force due to gravity?
Objects with more mass
How does the force due to gravity on earth change in relation to distance ?
It gets weaker as you get further away
What is newtons law of gravitation ?
the gravitational force of attraction between 2 point masses is separated by a distanace r
What is a gravitational field?
A region in space in which a massive object experiences a gravitational force
What is gravitational field strength and how is it represented?
The strength of the field which is measured in N/kg and field lines represent the direction and strength
What is a uniform field ?
The field is the same strength and direction in the whole area
How do field lines show a stronger field ?
When the field lines are closer together
Describe the gravitational field lines around a planet
Radial, equally spaced if uniform, pointing inwards
What is gravitational potential?
The work done per unit mass against gravitational force to move an object from infinity to a given point
What is the unit of potential energy ?
J/kg
What are equipotential lines ?
Lines that link points of equal potential
Equipotenital surfaces are always___________________to the gravitational field
At right angles / perpendicular
What happens when something moves along the equipotential lines ?
As it is travelling perpendicular to the field, no work is done so there is no potential energy change
What happens when something moves along a field lines?
It is moving parallel to the field so work is done so there is a change of potential energy
Why is the potential gradient negative?
Because potential increases as height increases so the field direction is downwards
What is 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
When is the potential 0?
At infinity
What equations do you equate to calculate escape velocity?
Kinetic energy and gravitational potential energy
What equations do you use for orbits?
circular motion and gravitational
What is a synchronous orbit?
Where the orbital period of the satellite is equal to the rotational period of the object that it is orbiting. e.g. for earth its period would be 24 hours
What objects does gravity act on?
Objects with mass
Is Gravity attractive or repulsive?
Always attractive
What happens when a object is moved from infinity to a point?
Energy is released as the gravitational potential energy is needed, therefore gravitational potential is always negative
What is gravitational potential difference?
The energy needed to move a unit mass between two points
What is gravitational potential difference equal to?
the work done. Work done=mV
How does the potential change on an equipotential surface?
It doesn´t, it is constant everywhere
What is the relationship between gravitational potential energy and the distance between the centre of the two objects?
Inversely proportional
How can gravitational field strength be measure from a graph of gravitational potential energy and radius?
by finding the gradient of the tangent and then multiplying it by -1
How can you find gravitational potential difference from a graph of field strength against radius?
The area under the graph
What is Keplers third law?
The square of the orbital period is directly proportional to the cube of the radius
How do you derive T²=kr³
make the centripetal force and gravitational force equal to eachother
What is the total energy of an orbiting satellite?
The sum of kinetic and potential energy.
Is the total energy of an orbiting satellite constant?
Yes
What is a Geostationary satellite?
They follow a geosynchronous orbit which means that they always stay above the same point on the earth because they are orbiting directly above the equator. For earth would also have a period of 24 hours
What are geostationary satellites used for?
Tv and telephone signals. Because it is always on the same point on the earth, you done have to alter the plane of an ariel or transmitter
What are low-orbit satellites?
They orbit lower and therefore travel much faster meaning their orbital periods are much smaller
What are the benefits of low orbit satellites?
they require less powerful transmitters and can cover more of the earths surface, they are useful for monitering the weather, making scientific observations about unreachable places and military applications
