Forces And Motion: Astronomy Flashcards
What does gravitational force cause?
- Causes planets to orbit the sun.
- Causes the moon and artificial satellites to orbit the earth.
- Causes comets to orbit the sun.
What does the moon orbit around?
The Earth.
What is gravity?
A force that pulls you down towards the earth and also pulls the earth towards the sun.
What does the gravitational force between two objects depend on?
Their masses and their distance apart.
How is the gravitational force on two objects relative to the distance between them?
It’s inversely proportional to the distance squared - i.e. as the distance doubles the force gets four times smaller.
How can you calculate orbital speed?
Average speed = distance moved/time taken
Distance moved would be circumference of the orbit so we can replace this with 2(Pi)r where r is the radius of the orbit.
So orbital speed = 2(Pi)*orbital radius/time period
How are a comets orbits different to a planets?
A comet has an elliptical (oval-shaped) orbit around the sun.
When will a comet travel fastest dusting its orbit?
Comets will travel fastest when they loop around the sun and then as they fly away the gravitational pull will decrease so they will move their slowest. It gains kinetic energy closest to the sun as that is where it is most pulled by gravity.
What is a galaxy?
A collection of billions of stars.
Which galaxy is the solar system part of?
The milky way galaxy.
What is the universe?
A collection of billions of galaxies.
How to remember the eight plants in order of distance from the sun?
My MERCURY Very VENUS Easy EARTH Method MARS Just JUPITER Speeds SATURN Up URANUS Naming NEPTUNE
Where is the asteroid belt?
Between Mars and Jupiter
Shape of the orbits of the planets
Elliptical (ovals) with the sun close to the centre
What’s gravitational field strength?
The strength of gravity on a planet or moon
On Earth it is 10N/kg
On the moon it’s 1.7N/kg
What does non luminous mean?
Example of non luminous object
They do not emit light
Eg the planets are non luminous objects: we see them because they reflect light from the sun
How are the planets held in orbit?
By the gravitational pull of the sun (eg gravitational pull on Mercury is v large compared to neptunes- therefore Mercury follows a more tight curved path than Neptune)
What are moons?
Natural objects that orbit a planet
Their motions (like planets) are determined by gravitational forces
They are also non luminous
How long does it take the moon to orbit the Earth?
29.5 days (1 lunar month)
While orbiting the earth it also spins on its axis, and it also completes a rotation every 29.5 days
Why do we always see the same half of the moon when looking up at the sky at night?
Because the time it takes to complete one orbit around the Earth is the same time for one rotation, the moon always keeps the same part of its surface facing the Earth
What are comets?
Comets orbit the sun
Approx 1-30km in diameter
Made of dust and ice
Describe a comets orbit?
Vague
Very elongated (v oval shaped) At times they are very close to sun, at others they are at the outer reaches of the solar system
Describe a comets orbit as it nears the sun?
The gravitational forces acting upon it increase and therefore it speeds up (whereas at the opposite end of the orbit it travels slowly)
They are most easily see near the sun
what is the tail of the comet?
Made up of the melted ice carrying dust (due to heat of the sun)
It’s what we see when we see a comet from Earth
Therefore comets are most easily see when they are close to sun (their tales are largest)
The tail is always being pointed away form the sun (because it’s flow of melt stuff)
