Fin Modification

Can you design a better fish?

Learning Objectives

After completing this lesson, the student will be able to diagram, compare and contrast the relative contributions to thrust from pushing, pulling, or flapping forces in tuna, jellyfish and stingrays.

Standards

  • NGSS-HS-PS2
  • NGSS-HS-Life Science
  • CCSS.Math.Practice.MP3

Supplies

  • Plastic tub
  • Ruler with cm/mm
  • 1x food coloring bottle
  • 2x fish models
    • 1 angelfish
    • 1 tuna fish
  • 1x Air-dry clay packet
  • Paper to write on
  • Something to record time (can use phone)

Fin Modification

This lesson is an extension to the previous experiment where you looked into how a fish moving its tail interacts with water. In this lesson, test your ability to design a better fish tail. To begin:

  • Retrieve the packet of air-dry clay that came with the kit.
  • Look at the fins already present on the bots and consider the fins of real-life fish. What are the benefits of having small, angular fins? What about big, showy ones? 
  • Create a few different tail shape types for your robot fish. The clay should adhere directly to the bot’s body, and it does not need to be completely dry to work for this activity, just firm enough to hold its shape.
    • As you add fins, you are adding weight as well. How does this impact the fish’s center of gravity?
  • To add the caudal (tail) fin, position it close to where the robot’s original fin is so the bot’s motor can still move it.
  • Repeat the previous experiment with the dye using the new tails, and see how the flow of water changes using food dye. Observe how much force each fin type produces, and take note of how the flow behaves – is it turbulent? Is there a lot of splashing?
    • Don’t worry so much about recording data here, this is more so for observation.
    • You are encouraged to try out multiple fin shapes and sizes here!
  • In nature, high speed swimmers like tuna fish have a high aspect ratio between their tail and the attachment point (caudal peduncle), meaning their bodies narrow out towards the back and then have a tall and thin tail. 
  • Slower swimmers have a lower aspect ratio. The height of their tails is similar to the height of the attachment point.
    • Did you notice this same concept apply in the activity? Why do you think aspect ratios matter?

Next Steps

Now that you have a solid grasp on basics of fish movement, hop back to the movement lesson plans to dig into hydrodynamics in more detail.

A Day in the Life
Form and Function
Balance
Movement
The Literate Engineer

Last updated: November 23, 2022.