Gravity and Orbits Flashcards
Describe the orbits of moons.
Slightly elliptical
Describe the orbits of planets.
Slightly elliptical
Describe the orbits of comets.
Very elliptical with the Sun at one focus (near one end of the orbit).
Why does a comet travel faster when its nearer the Sun?
Because the increased pull of gravity makes it speed up the closer it gets to the Sun.
What is a geostationary satellite?
An artificial satellite with orbital period of exactly one day.
How do you calculate speed of an orbit?
speed = distance/time
How do you calculate circular orbit speed?
Distance = circumference
so 2 x pi x r (r being the distance from the centre of the object you are orbiting)
So
v = 2 x pi x r /T
T measures in sec
CHECK UNITS in the question and convert before you calculate.
Why are geostationary satellites useful?
These are useful in communications because they are always over the same part of the planet.
Describe the change in orbital speed of a comet.
A comet travels much faster when it is nearer the Sun than it does in the more distant parts of its orbit.
The structure of the Solar System is determined by …
…Orbits - the paths that objects take as they move around each other in space.
Describe the path that planets move around the Sun.
Almost circular orbits.
If an object is travelling in a circle…..
…. it is constantly changing direction (and so constantly accelerating), which means there is a force acting on it. (F=ma)
What is the name of the force causing the object to travel in a circle?
Centripetal force (acting towards the centre of the circle).
Why doesn’t the object just fall towards the centre of what it is orbiting?
Because the object is already moving, so it just causes it to change direction.
The object keeps accelerating towards what its orbiting but the instantaneous velocity (which is at right angle to the acceleration) keeps it travelling in a circle.