Question

you can see how gravity and speed combine to cause an orbit in the following diagram: the green object’s speed equals the force of gravity that pulls it toward the blue object. it is always falling toward the blue object, but its speed keeps moving it away from the blue object. the two forces are balanced, so the green object moves in a stable orbit. this phenomenon causes moons to orbit planets, planets to orbit stars, and stars to orbit the centers of galaxies. earth, moon, and sun system gravity and speed also combine to cause all the apparent motions of the sun and moon in our sky and the changes in our seasons. earth spins around an imaginary line called the rotation axis. this axis connects the north and south poles. this rotation causes earth to spin once every 24 hours (1 day). so at any moment, exactly half of earth faces the sun (daytime) and half faces away (nighttime). earth’s rotation also causes the apparent motion of the sun and moon in our sky. the sun does not orbit earth and it takes the moon 29.5 days to orbit earth. this means that our daily rotation changes our view of them. patterns and scale: the diagram shows a two - body orbit. look back at the photograph of the spiral galaxy. how do gravity and speed affect this giant system of stars and gases? key concept: the sun and moon are different distances from earth and different sizes. explain why we see both of them move across our sky once every 24 hours.

Explanation:

1. For the first question about the spiral - galaxy: Gravity provides the centripetal force that pulls stars and gases towards the center of the galaxy, while their speed gives them the necessary tangential velocity to avoid falling into the center. This balance allows stars and gases to maintain their orbits within the galaxy.
2. For the second question about the Sun and Moon moving across the sky every 24 hours: Earth rotates on its axis once every 24 hours. As Earth rotates, from our perspective on Earth, it appears as if the Sun and Moon are moving across the sky, even though the Sun is stationary relative to Earth's rotation and the Moon orbits Earth over a longer period (29.5 days).

Answer:

1. Gravity provides centripetal force and speed gives tangential velocity to keep stars and gases in orbit in the galaxy.
2. Earth's 24 - hour rotation makes the Sun and Moon appear to move across the sky.