Practice Questions

1.State the name of a force that keeps one object in orbit around another.

Gravity

2.Explain why the speed of the Earth orbiting the Sun is constant, but its velocity is constantly changing.

The speed of the Earth orbiting the Sun is constant because the Earth travels at a steady rate along its orbit. Speed is a scalar quantity, so it only depends on the magnitude (how fast something is moving), not the direction.

However, velocity is a vector quantity — it depends on both speed and direction. Even though the Earth’s speed stays the same, its direction of motion is constantly changing as it moves in a nearly circular orbit around the Sun.

This continual change in direction means that the Earth’s velocity is constantly changing. The reason the direction changes is because the Sun’s gravitational force pulls the Earth toward the center of its orbit. This force acts at right angles to the Earth’s motion, causing a change in direction (centripetal acceleration), not speed.

3. If a planet has two moons, one in low orbit and another in a higher orbit. Explain why the lower orbit moon travels faster

The moon in the lower orbit travels faster because it experiences a stronger gravitational force from the planet.
Gravitational force increases the closer an object is to the planet. To stay in orbit at a lower altitude, the moon must move faster to balance this stronger gravitational pull. If it moved too slowly, it would spiral inward and crash.

In contrast, the higher moon feels a weaker gravitational pull and doesn’t need to move as fast to stay in orbit.