(b) Motion in the universe ​

• A universe is a collection of billions of galaxies
• A galaxy is a collection of billions of solar systems
• A solar system contains stars and planets
• Gravity is a force that pulls all objects close to the surface of the planet towards the planet. The force of gravity depends on the inner core of the planet and since this varies from planet to planet, the gravity at each planet varies. Compared to Earth, the Moon has a weaker gravity whereas Jupiter has a much larger gravity.
• Gravity is responsible for keeping the moon, the planets, satellites, and comets in orbit.
• Planets orbit in a circular shape around a star as shown in figure 1
• Comets orbit in an ellipse shape around a star. The speed of the comet increases as it becomes closer to the star. This is shown in figure 2
• Moons orbit planets as shown in figure 3.

Figure 1

Figure 2

Figure 3

Important equation to keep in mind!!!