Why doesn't the Earth fly off into space?

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SWBAT describe why the Earth stays in orbit around the Sun.

Big Idea

Gravity is the force that keeps the planets in orbit around the Sun and the Moon orbiting around the Earth.

Lesson Overview- 5 E Lesson Plan

5 minutes

Unit 3: Gravity

Lesson 1: Why Doesn’t Earth Fly Off Into Space?

5E Lesson Planning:

I plan most of my science lessons using the BSCS 5E Lesson Model: Engage, Explore, Explain, Elaborate, and Evaluate.For a quick overview of the model, take a look at this video.

I use this lesson model because it peaks the students' interest in the beginning during the "Engage" portion and allows for the students to actively participate in the investigations throughout the subsequent steps. The “Evaluate” component of the 5E Lesson Model can be used in many ways by the teacher and by the students.

A great resource for lesson plan frameworks and explanations is the Community Resources for Science. The 5E Lesson Planning Template and 5E Lesson Planning Prompts come from this website.

Unit Overview:

In this Unit students will conduct some investigations about gravity. They will learn about how the planets stay in orbit around the Sun and will re-create Galileo’s pendulum experiments. They will also learn about Sir Isaac Newton’s work and his Laws of Motion as they relate to the idea of gravity.

Lesson Overview:

In this lesson, students will observe a demonstration about the Earth’s orbit around the Sun and I will introduce the terms gravity, gravitational attraction and mass. Students will do a simple investigation re-creating Galileo’s work with dropping objects from a height and seeing how fast they dropped.

Next Generation Science Standards:

The NGSS standards that will be covered in this unit/ lesson are:

5-PS2-1. Support an argument that the gravitational force exerted by Earth on objects is directed down.

Disciplinary Core Ideas:  This lesson aligns to the Disciplinary Core Idea of

PS2.B: Types of Interactions  The gravitational force of Earth acting on an object near Earth’s surface pulls that object toward the planet’s center. (5-PS2-1)

Crosscutting Concepts:

Cause and Effect:  Cause and effect relationships are routinely identified and used to explain change. (5-PS2-1)

Science & Engineering Practices:

Engaging in Argument from Evidence

Engaging in argument from evidence in 3–5 builds on K– 2 experiences and progresses to critiquing the scientific explanations or solutions proposed by peers by citing relevant evidence about the natural and designed world(s).  Support an argument with evidence, data, or a model. (5PS2-1)


20 minutes

We have just finished our Solar System Unit (The Sun Earth Connection) and the students had a lot of questions about why and how the Earth doesn't fly off into space. They also wondered why humans don't fly off into space and why we don't feel the Earth rotating. I told them that we will be studying a unit that describes these phenomenon and that we will be completing investigations about this.

I start the lesson by telling the students to watch what I am going to be doing and to think about what it is I am demonstrating. I remind them about the lessons we have just finished about the Solar System and ask the students to try to connect my demonstration to those lessons. I also have the students write any questions they have and to draw or write about the demonstration.

I take a plastic ball (Wiffle Ball) and tie one end of a string to the ball. The string is about 1 meter in length (the length of the string should be long enough so that you can swing the ball around above your head). I make sure that there is space above my head and around me so that I don't knock anything over. 

I start swinging the ball around and above my head and tell them to watch and think about what it is I'm demonstrating. After doing this for a minute or so, I tell the students to write down their thoughts about what I am demonstrating. I remind them that there are no right or wrong answers, but that they are coming up with a hypothesis about the demonstration. After about a minute or 2 of writing, I have the students do a "Stand-Up, Hand-Up Pair Up". They stand up with their notebooks and I play some music so they can walk around and meet up with a partner. They walk around silently and when the music stops, they meet with the person that is closest to them. I remind them of our guidelines for this- CHAMPS (they don't follow their BFF around so they can talk to them, they don't turn away from the person that is nearest to them, and they welcome anyone who doesn't have a parnter).

I give each student 30 seconds to share their thoughts about what I was demonstrating. I let them mix up again to talk to another student and then the students return to their desks.

I ask the class to share any ideas that came up and I write them on the board:

  • The ball is the moon and your head is the Earth and the Moon is spinning around the Earth
  • You are the Sun and the Ball is the Earth
  • The Ball is flying around
  • The string is the gravity pulling the ball that is representing the Earth and this keeps it orbiting around the Sun.

I then ask the students what would happen if I let go of the string and the students tell me that the ball would go flying off. I then demonstrate this by letting go of the string and having the ball fly off. Of course I make sure that I let go of the ball in a direction where it won't hit any of the students or knock anything over. It might be a good idea to do this outside. 

After I let go of the string, I ask the students to describe what direction the ball flew in and to write this in their Science Notebooks.


Explore/ Explain

20 minutes

We then talk about the demonstration and we review the term revolution or orbit. I tell them that the ball is the Earth and that my head is the Sun and I ask them to talk in their groups about what is happening in more detail. I ask them to use the terms that we learned in the Solar System unit. 

I ask for someone from each group to describe the Earth's path around the Sun and what was causing this. Most of the groups describe a circular or round pattern of Earth's movement around the Sun. A few students also note that the Moon makes this same movement around the Earth. I also ask them about what the string is representing (if they don't come up with this themselves). The string is a force that is pulling the Earth towards the Sun. I tell the students that the string is a representation of this pull of gravity and the the gravitational attraction of the Earth towards the Sun changes its direction of travel so that it revolves or orbits around the Sun.  I also ask the question as to why the Sun is able to have this "pull" and some of the students come up with the fact that the Sun is so much larger than the Earth (and the other planets) that it is able to keep them in orbit around it. 

I ask the students to draw the demonstration in their Science Notebooks and we then add the following terms to our notebooks and our new Word Wall:

force, gravity, gravitational attraction, orbit, revolution

(insert photos of notebook entries and word wall).




Elaborate and Evaluate

15 minutes

I then tell the students that we will be conducting some investigations similar to the ones that Galileo Galilei conducted in the 16th Century. I show them a short video about Galileo from the Biography Channel and tell them to take 3-2-1 notes as they watch the biography. The 3-2-1 Notes are a note taking strategy that I have used with my students for when they are either reading an informational text, listening to a lecture, or as in this case, watching a video. I have the students write down 3 things that they learned, 2 things that they found interesting, and one question that they might have about the video. It is a great strategy to use to get the kids to pay better attention to a video, lecture or when they are reading.

I have the groups conduct a "Round Robin" discussion after viewing the video to share something that they thought was interesting about Galileo. As they are having their discussions I walk around to listen to the groups and I record some of the items they found interesting and keep track of any students who may be having difficulty. 

Several students were intrigued by his experiments-especially his Leaning Tower of Pisa experiment and his discoveries in astronomy. They also discussed the idea that it's important to conduct experiments to prove a hypothesis.