Gravity and Motion
A planet suddenly moves closer to its star. Predict how both its speed and orbital path will change.
Its speed will increase, and the orbit will become tighter (closer to the star).
A galaxy has no clear shape and seems chaotic.
What might have caused it to form this way?
A collision or interaction with another galaxy.
Explain why accretion happens faster near the center of the solar nebula than farther out.
Higher density of particles near the center means more collisions and faster growth of planetesimals.
A movie shows a spaceship being sucked straight into a black hole. Explain why this is not accurate.
Objects spiral in due to gravity and forward motion; they are not pulled straight in like a vacuum.
You drop a small piece of dust into a whirlpool and watch it spin toward the center.
Is this example showing something at a small scale or large scale in space? Explain.
Small scale; it models particles moving toward the center of a forming solar system.
Two planets orbit a star. One is 1 AU away, the other is 4 AU away.
Which planet will orbit faster, and why?
The planet closer (1 AU) will orbit faster because gravitational pull is stronger nearer the star.
Compare spiral and elliptical galaxies in terms of star formation. Which forms new stars, and why?
Spiral galaxies form new stars because they have gas and dust; elliptical galaxies mostly have older stars and little gas.
Why does a collapsing nebula start spinning faster as it contracts?
Conservation of angular momentum — as the cloud shrinks, rotation speed increases.
Why is a black hole not “empty space,” even though nothing can escape from it?
It contains extremely dense matter, and gravity is concentrated at a point called the singularity.
A telescope observes 7 planets in the Kepler-90 system.
Which is the largest-scale observation here: the star, the planets’ orbits, or individual rocks on a planet? Explain.
The star and planets’ orbits; the individual rocks are too small to observe at this distance.
You drop leaves in a whirlpool and they spiral inward.
Explain why this is similar to how objects orbit a star, including forward motion.
Objects move forward while gravity pulls them inward, creating a curved orbit instead of falling straight in.
If Earth were in an elliptical galaxy instead of the Milky Way, how might the night sky look different?
The sky would have fewer bright stars and no spiral structure; star density might be lower in some areas.
A shockwave from a supernova hits a gas cloud. Explain how this could trigger the formation of a solar system.
The shock compresses the cloud, starting gravitational collapse and spinning motion, initiating formation.
Describe what happens to light near a black hole, and how this might affect what we see.
Light bends, and objects appear stretched or displaced; some light cannot escape.
Scientists measure the time each Kepler-90 planet takes to orbit its star.
If planet A is closer to the star than planet B, how should their orbital periods compare according to the data?
Planet A’s orbital period should be shorter than planet B’s; closer planets orbit faster.
If the Sun lost half its mass, how would this affect the orbits of all planets? Explain why.
Planets would move outward and orbit more slowly because gravitational pull would be weaker.
Explain why the Milky Way appears small when shown with other galaxies on a Large Scale map, even though it is huge.
Because other galaxies are much farther away or are much larger, so the Milky Way looks small in comparison.
Compare the formation of rocky planets to gas giants. Why are gas giants farther from the Sun?
Gas giants formed where it was cold enough for gases and ices to accumulate; closer to the Sun it was too hot.
Explain the role of the accretion disk around a black hole.
Matter spirals around the black hole, heating up and emitting energy before crossing the event horizon.
Compare the size of the Milky Way galaxy to Earth.
Which is small scale and which is large scale, and why is this distinction important when looking at maps of galaxies?
Earth is small scale, the Milky Way is large scale; maps must show galaxies proportionally, so Earth is not visible.
A planet has an elliptical orbit. At which point does it move fastest, and why?
At the point closest to the star, because gravitational pull is stronger and it speeds up.
Two galaxies are approaching each other. Predict what will happen to their stars, gas, and shape over time.
They will interact gravitationally, possibly collide, distort shapes, form new stars, and eventually merge.
Explain why planets in our solar system orbit the Sun in roughly the same plane and direction.
The original gas cloud flattened into a rotating disk; conservation of angular momentum caused aligned orbits.
Why do astronomers say a black hole can affect nearby stars without “touching” them?
Gravity extends beyond the event horizon, so stars orbit or are pulled by gravity without direct contact.
You are given a table of planet sizes, distances, and orbital periods for Kepler-90 and the solar system.
Use the data to predict the orbital period of a planet farther from the star than any listed planet. Explain your reasoning.
The planet would take longer to orbit than the outermost planet in the table because orbital period increases with distance.