Motion in the Solar System

In this lesson, students create a model solar system to observe the motion of planets and how the force of gravity affects their orbits. Once students understand how all matter is made up of atoms and can change when heat is added or removed, they analyze how gravity is an attractive force between all matter and depends on the masses of the different objects. Specifically, they discuss how the sun’s gravity holds all of the planets of our solar system in orbit around it because the sun is so much more massive than the other objects in the solar system.

• Scientists continue to learn about our solar system— a collection of planets and other objects that orbit around a star.
• Earth is one of eight known planets in the solar system, and these planets are all made up of different kinds of matter.
• All matter has gravity, which is an attractive force between all matter.
• Gravity is the force that holds the solar system together.
• The sun is the most massive object in our solar system, so its gravity pulls all of the planets and other objects in the solar system into orbit around it.
• The sun’s gravity determines the motion of the planets in orbit around it, while the gravity of individual planets determines how many moons will orbit each planet.
  
  

• How are the properties of the four planets closest to the sun different or similar to the four planets that are farthest from the sun? Why do the planets have different colors?
• Why do different planets have different masses?
• Why do scientists use scale models of the solar system, similar to how scientists use models of the atom?
• Why is gravity an attractive force?
• How does gravity affect you here on Earth?
• How does the sun’s gravity affect planets in our solar system?
• How does the force of gravity affect how quickly a planet orbits the sun?
• Why does it take Mercury 88 Earth days to orbit the sun, while it takes Neptune 165 Earth years?
  
  

Misconception: Only Earth has gravity.

Fact: All matter has gravity. All objects near Earth’s surface are pulled on by Earth’s gravity because Earth is the most massive object near us.

Misconception: Earth doesn't move in the solar system. 

Fact: The sun’s gravity keeps Earth and the other planets in orbit.

Misconception: If an object is at rest, no forces are acting on it.

Fact: Forces are constantly acting on objects both at rest and in motion. 

Atom : the smallest piece of matter that has the properties of an element; a combination of three subatomic particles: protons, neutrons, and electrons

Cause and Effect : a relationship between events or things, where one is the result of the other

Force : a push or pull that acts on an object, changing its speed, direction, or shape

Gravity : a force of attraction between all matter

Mass : a measure of the amount of matter that makes up an object; a property of matter

Matter : everything that has mass and takes up space

Pattern : something that happens in a regular and repeated way

Scale : the size, extent, or importance (magnitude) of something relative to something else

Science : all knowledge gained from experiments

Solar System : a collection of planets and other objects that orbit a star

Weight : the gravitational force exerted on an object by a planet or moon

Wanderers

Every night, Mars appears to move across the sky. It appears as a red dot that moves from west to east. It moves because Mars is a planet. The word “planet” comes from a Greek word that means “wanderer.” Planets are made up of combinations of the same elements that make up matter on Earth.

Scientists today define a planet as a body that orbits the sun, is massive enough for its own gravity to make it round, and has cleared out smaller objects around its orbit.

There are eight known planets in our solar system. A solar system is a collection of planets and other objects that orbit a star. Scientists use models to study the solar system in the same way that they use models to study atoms. They do this to see how the different parts of the solar system work together.

Planets in Our Solar System

The eight planets are divided into two groups. Each group shares certain properties.

• The four planets closest to the sun are called terrestrial planets. They are Mercury, Venus, Earth, and Mars. These four planets are solid balls of rock. Earth is the only planet known to support life.
• The four planets farthest from the sun are called gas giants. They are Jupiter, Saturn, Uranus, and Neptune. These planets are mostly gasses. The gas giants are also orbited by colorful rings made of rock, dust, and ice. They have many moons.

For the hands-on activity in this lesson, students create a model solar system to observe the positions of the different objects in the solar system relative to each other, the motion of planets, and how the force of gravity affects their orbits. Students use their solar system models to analyze how gravity causes patterns in the movement of all objects in the solar system.