Lesson 1: Orientation, stability, and how to keep your bearings

Author: Dr. Johanna T. Ohlmeyer
Lesson 2 in the Integrative Sciences: Biology-Physics series
[ezcol_1quarter]Main Idea:[/ezcol_1quarter] [ezcol_3quarter_end]Organisms continuously orient, know where is up/down, and constantly adjust its center of gravity in relation to its environment. This involves interactions between the neurological function of proprioceptors and the physical forces that constantly act on that body. Organisms have come up with several solutions that necessitate morphological changes in order to meet physical laws.


[ezcol_1quarter]Objectives:[/ezcol_1quarter] [ezcol_3quarter_end] 1. To revise the fundamentals of gravity, force, and proprioception.
2. To understand the roles that these principles play in the biological concept of stability.
3. To construct activities aimed to show understanding and application of these concepts.[/ezcol_3quarter_end]

[ezcol_1quarter]Students’ Skills:[/ezcol_1quarter] [ezcol_3quarter_end]Observation, inquiry, exploration, analysis, integration, applicability, making use of knowledge, synthesis: These skills were drawn from Bloom’s Taxonomy and the constructivist list. NGSS connections: MS-LS2 Ecosystems: Interactions, Energy, and Dynamics; and MS-LS4 Biological Evolution: Unity and Diversity.[/ezcol_3quarter_end]

[ezcol_1quarter]Materials[/ezcol_1quarter] [ezcol_3quarter_end] 1.  For the lecture: textbooks, material reference, index cards.
2. For the activity: handouts, objects of different shape: rectangular box, sphere, oval, rod, narrow, and wide sticks and one stick with holes at one end. Toothpicks, pencils with one end blunt to serve as legs.[/ezcol_3quarter_end]

[ezcol_1quarter]Lesson:[/ezcol_1quarter] [ezcol_3quarter_end]1. Entry card and in response to the following prompt, write 2-3 sentences and provide an example: What do you think the term “gravitationally stable” means? Allow time for the students to ponder and to write down their answers. Follow it by a discussion leading toward listing the characteristics that make an object unstable, stable, or neutral. Make a list of ideas on the board.

 2. Before students explore these ideas further, review the concepts of gravity, force, F=ma, weight, mass, potential energy, and center of gravity. Found out the students’ prior knowledge and misunderstandings by targeted questions or prompts. Keep this information on the board.

3. Explain to students that they are going to work in groups of 2-3 students and that they will experiment with some inanimate objects first and then with a live organism.

 4. Give to each student a work sheet and explain how to fill the table using as an example the first column.  There are three parts in the activity. First, the idea in this part is to have the students explore the idea of equilibrium using several objects and to classify them into unstable/stable/neutral.  The first part helps the students understand the relationship between gravity, the center of gravity, footprints, and stability. In the second part, working in groups of 2-3, students will further explore how a wide base of support and legs in an animal affect stability but help movement. In the third part the students will use their own bodies to challenge their stability and explore the role of their proprioceptors, nervous system, balance organs, and their muscles.

5. Encourage the students to ask questions, answer any questions, ask the students to start working in the activities, discuss their findings among them, and fill the table as a group.

6. Circulate among the groups, fill content gaps, and make sure they understand what are they doing.

7. Leave enough time for student and class reflection. Foster students’ participation and invite them to share their answers and discuss their ideas as a class.

8. Exit card: Write two things you have learned today, two questions, and one suggestion.[/ezcol_3quarter_end]

[ezcol_1quarter]Class Closing:[/ezcol_1quarter] [ezcol_3quarter_end]
1. Collect entry/exit cards.

2. Homework: Go over the handout of today and finished if it is not completed. You may add any further ideas.  Bring the finished handout to class.

3. Write a small paragraph addressing the following question: What do you think was the purpose of this lesson?


[ezcol_1quarter]Assesment:[/ezcol_1quarter] [ezcol_3quarter_end]
1. Participation in class and discussions.
2. Grading: completeness and thoroughness filling the activity handout and index cards.
3. Use a general rubric to evaluate students’ overall performance.[/ezcol_3quarter_end]

[ezcol_1quarter]Teacher’s Reflections[/ezcol_1quarter] [ezcol_3quarter_end]
1. Things that I did not cover.
2. Did I meet the lesson objectives?
3. Comments, conclusions, and modifications
4. Pedagogical value of the lesson. Did my students learn the concepts and ideas explored in this class? Did the assessments provide enough evidence of understanding?[/ezcol_3quarter_end]

[ezcol_1quarter]Notes to the Teacher[/ezcol_1quarter] [ezcol_3quarter_end]
1. Make sure the students understand the concept of one part of the lesson before going on to the next. This lesson may take more than one class period. Part III would be better if left for the next class since it integrates the concepts and applies them. Teacher involvement in facilitating and providing support to students as well as group/class discussion is important.

2. The lesson can be modified to make it simpler for middle school children by using only the box and the sticks part of the activity. Also it can be more difficult for high school students by adding the quantitative dimension (measuring angle at which the object became unstable, turning momentum versus angle) and more discussion of the involvement of the nervous system.

3. The take home message is that bodies that are under gravitational force are stable, unstable, or neutral in position depending on their mass distribution with respect to their footprint.

4. The tree elements for increasing stability in objects are: weight near the base, low center of gravity, and wide base.

5. Basically an object is stable if; the force applied elevates the center of gravitation, increases potential energy, and the restoring force brings the object to the original position.

6. Living organisms have high gravitational center because the need of legs for locomotion. In animals, the force that constantly counteracts unstable positions, is created by opposing muscles contracting and relaxing. This is coordinated by our nervous system (balance: inner ear, proprioceptors).

7. The student activities are designed so that the students arrive to these understandings by exploring the possibilities, by interacting with their peers, and answering the questions in the handout.

8. Thus reflection and in-group discussion is necessary. Appropriated coaching and help should be given by the teacher, hence circulating and engagement with small group of students is of crucial importance.


Laws, K., & Sugano, A. (2008). Physics and the Art of Dance: Undestanding Movement (Vol. Second Edition). Oxford University Press.
Tipler, P. A. (1999). Physics for Scientists and Engineers (Vol. fourth Edition). Freeman/Worth Publishers.
Vogel, S. (2009). Glimpses of creatures in their Phisical Worlds. Princeton University Press.




Today we are learning about Orientation and how to keep your bearings.


Organisms continuously orient themselves, know where is up/down, and constantly adjust its center of gravity in relation to its environment.  Today we are exploring some of the physical laws that act on objects and organisms. We are going to find out how do we keep our bearings.



Part I: In this exercise you will classify each object (a-f) in the chart below as stable, unstable or neutral. In order to decided how to categorize them, take in consideration the following points and write your reasons in the appropriate space.

1. Is the base (contact with the table) narrow or wide? What shape is the footprint or area of support?

2. Is the weight evenly distributed? Draw the arrow indicating the center of gravity and the force of gravity.

3. If the object is displaced (see figure), how easily does it get out of equilibrium? Describe what happens.

4. When the object is displaced, does the center of gravity change (distance from the table)? Is there a change on potential energy?

5. What is the preferred orientation of the object?



box example


























Part II:

Now that we have explored the idea of center of gravity, let us think about mass distribution in relation to footprint and look at (g) and (h) closer.

Classify them following the same steps as in part I.













g) Answer the following questions comparing the results between the stick standing on the solid narrow end and the stick standing on the holed narrow end:

Where is the center of gravity in each case?



What does your results suggest about the center of gravity and stability?



h) Answer the following questions comparing the results between the object standing on the small base end and the object standing on the wide base:

Where is the center of gravity in each case?


What does your results suggest about the center of gravity, stability and unipeds (birds standing on one leg)?



j) Pick two spheres, two ovals, or two blocks. Draw their footprints in a piece of paper and insert long sticks in one object and short toothpicks in the other mimicking long and short legs. Play with the number of “legs” and the distance between them. You are mimicking an animal in stilts.

What happens if the “legs” are inside versus the outside of the footprint? Describe your results



Where is the center of gravity?



Describe the situation where your shape is most stable?



Part III:

If you try to stand or walk in stilts, you may find it very difficult. Why do you think that is the case?



As we have learned by experimenting with objects, a body is balanced if the center of gravity is directly above the footprint or area o support (table, floor).

While you perform the activities below, think of what object (a-h) exploration you did most resemble the action.







When you are standing on two feet pointing forward and separated hip-wide, where is you center of gravity?



What happen to your center of gravity if you extend one leg to the side? What direction do you have to move your mass/weight in order to stay in balance?




How has the area of support changed from a to b?





Standing with your two feet pointing forward, have another student push you forward and sideway from the shoulders. Describe how your balance is affected, put attention on how your body and your leg muscles react. What happens?



Repeat (d) but with your heels touching and your toes pointing outwards like a v.


Finally, standing on two feet pointing forward, try to go on your tipi-toes. Are you in balance? Then keeping on mind that the center of gravity must be always pointing directly down to the center of your footprint, slowly go again in your tipi-toes. Is there any difference on your stability? What happen to your leg muscles? What happens if you close your eyes?