5.3 Gravitational Fields Flashcards
What are gravitational fields due to?
Objects having mass
What are gravitational field lines?
Show direction of the force that masses would feel in a gravitational field
What is a gravitational field?
Region where objects experience a non contact force
What are some properties of gravitational fields?
Force felt in field is Always attractive
It’s a vector
What is Newton’s law of graviton?
F=-GMm/r^2
What is gravitational field strength?
Force per unit mass
Where is gravitational field strength uniform?
Surface of earth
What is Kepler’s first law?
Each planet moves in an ellipse around the sun, with the sun at one focus
What is Kepler’s second law?
A line joining the sun to a planet will sweep out equal areas in equal times
What is Kepler’s third law?
The period of the orbit and the mean distance between the sun and the planet are related by Kepler’s third law, T^2 proportional to r^3
What provides the centripetal force on a planet?
The centripetal force on a planet is provided by
the gravitational force between it and the Sun
How do you derive the equation
T^2=(4pi^2/GM)r^3
Use F=-GMm/r^2
F=mv^2/r and v=2pir/T
What are geostationary satellites?
Orbit directly over the equator and are always above the same point on Earth
What is the angular speed of a geostationary satellite the same as?
Same angular speed as the Earth turn below it
How long does a geostationary satellites orbit take?
24 hours
What are the uses of geostationary satellites?
Sending TV and telephone signals improving communication in the world
Why don’t you have to alter the angle of receivers or transmitters on earth?
The satellite is stationery relative to a certain point on the Earth
What are the downsides to satellites?
They are expensive and pose a small risk of falling back to Earth
How can Newton’s law of graviton help to explain the thickness of a planets atmosphere?
Planets gravitational field exerts a force on everything around it, including the particles which make up its atmosphere (otherwise particles would float up to space)
The bigger the planet, the larger the force is further from the planet’s surface, so the more atmosphere particles it can stop escaping into space
So thicker atmosphere
Define gravitational potential
the work done in bringing unit mass from infinity to the point; gravitational potential is zero at infinity
Describe a force distance graph due to the gravitational field of a point mass, what is the area underneath?
Decreasing negative gradient, (starting from r1)
Area underneath is work done
Define escape velocity
Velocity needed so an object has just enough kinetic energy to escape a gravitational field.
When does an object have a high enough escape velocity?
When an object kinetic energy is equal and opposite to its gravitational potential energy, so total energy is Zero
How do you derive equation for escape velocity?
1/2mv^2 + (-GMm/r) = 0
Cancel cancel
V=root(2GM/r)
