Fin Activity

This lesson seeks to answer the questions

How can I design a rocket that flies straight up without wobbling?

How can fins help correct a rocket's flight when it starts to rotate?

Where should fins be placed on my rocket?

Activity 1: Why is wobbling bad for my rocket?

Have a conversation with the group to motivate the reason for adding fins to a rocket. Ask the group the questions in blue, guide their answers toward the italicized concepts.

What is our goal when we design rockets today?

GOAL: Design a rocket that flies as high as possible.

Select a volunteer from the group and hand her a paper model of a rocket (no fins, just body and nose cone).
Can you trace in slow motion the path of an ideal rocket flight?

This should look something like a straight path in which the rocket never rotates, wobbles, etc.

Can we always expect a rocket to fly straight up right off the launch pad?

Probably not.
The launch pad might be crooked, the rocket might be a little heavier on one side, etc.

What happens if the rocket starts to rotate or wobble a little?  Will this help us reach our goal?

No! If it rotates, there might be more surface exposed.  This would create stronger drag.
This stronger force would push it back to the ground, and it wouldn't fly as high!

Activity 2: How can I correct rotation on my rocket?

Continue the above conversation.  The goal now is to explain why adding fins will help build a higher-flying rocket.

Is there anything we can do to correct accidental rotation or wobbling? What if you could use your hands in mid-air, what would you do?

Use hands to push the rocket back to a straight orientation.

But we can't really do this with our hands in mid-flight, can we?  What other force could we use?
What force have we talked about earlier?

Drag! (This might be difficult for kids to figure out).

Exactly! Drag isn't always a bad thing.  We can actually use a drag force to correct any wobbles or rotations that happen to the rocket.  How could we add an extra drag force to the rocket? (Hint: What does a drag force push against?)

Add surface area! Add fins!

Explain that fins helps create a drag force push in the right place that will correct any wobbling that happens.

Activity 3: Where should I place my fins?

A particular challenge of understanding why adding fins is understand why placement along the body of the rocket matters. Fins at the nose of the rocket will be worthless, but fins at the base will provide the corrective force that helps achieve high-flying rockets.

This interactive, hands-on demo helps students master this concept by letting them feel and observe firsthand the influence of fin placement on rocket orientation.


Here's a video demo showcasing the intended interaction of this activity. 

Note that a key piece of understanding is observing how each model differs in its behavior when you release it from a straight-ahead position into the fan (e.g. "drag force"). Make sure students understand that the rocket's goal is to fly in the direction of its big red arrow, the fan is acting as the drag force, and their job is to determine which fin arrangement will harness this force to correct any errors in the wobbliness or rotation of the rocket.


Divide students into groups of three or four.  Give each the materials listed below.

Instruct them that the fan is acting as the drag force experienced by the rocket. Have students turn on the fan. 

Ask each to choose a single model and make a prediction about it.  What will happen with this rocket is placed facing straight-ahead into the fan? What will the drag force do?  Will the rocket maintain a stable course or rotate away?

Have the students manually hold the rockets in place and then let go.  Record their observations and discuss.

Repeat for the second model.

After each student has had a chance to experiment and play with both models, regroup.  Ask the class to explain which placement (base or nose) is best, and why.  Make sure their explanations use concepts of drag, rotation, and correction.


Each group of students will need:
  • 2 model rockets (use plastic water bottle as base).
    • 1 with fins placed near base
    • 1 with fins placed near nose
    • Place wooden dowel axis through center of mass of each bottle.
    • Adding giant arrows pointing in direction of flight helps clarify the "ideal" orientation.
  • Powerful table top fan.
    •  Vornados work well in our experience.
    • Most common table top fans aren't really strong enough (at least in our tests). Make sure the fan pushes the bottle to rotate easily around its dowel.  If you struggle to find a strong enough fan consider smaller models or WD40 lubrication to make the rotation easier.