## Introduction: Balloon Rocket Cars

I am always looking for an easy project I can do in a classroom of 30+ kids. If I can quickly put kits together, that's great, but many projects, especially when preparing for 30+ kits, take a lot of work and time. So, when I found a kit for this project for $1.20/kit, I jumped on it and bought 4 sets of 10 kits. But I realized that I could probably put a kit together cheaply with every day materials.

Putting the vehicle together took matter of minutes, which was great since I only had an hour for the project. Then they were asked to power it by attaching a balloon to it. They were given a choice of two different sized balloons as well as complete freedom to shape and attach the straws whichever way the students wanted to try. I like to tweak things a bit, forcing the students to figure things out on their own.

The students had a fantastic time trying out different weights, sizes, attachments and learned while having fun. Unfortunately, we didn't have enough time to try out the incline surfaces and frictional losses. But, I'm looking to continuing with it during next school year.

I hope you’ll have fun with this project!

## Step 1: Your Supplies List

For Vehicle:

- 1 Corrugated plastic or cardboard piece for the vehicle body (3 in x 5 in)
- 2 Plastic coffee stirrers
- 1 Plastic drinking straw, cut in two equal pieces
- 4 Foam disks for the wheels (~ 2.5 in in diameter and 0.5 in thick), but if you can't find these, you can cut them out from the same corrugated cardboard
- Tape

For Rocket Balloon Power:

- 1 Plastic drinking straw
- 1 Balloon any size, but I took balloons of various sizes to the classroom to show the students the difference in air-power (also, to show them that BIGGER isn't always BETTER)

## Step 2: Making the Vehicle Chassis

- I used a delivery cardboard box to cut out my vehicle chassis (3 inches x 5 inches).

I was able to cut out several fairly easily and quickly. But I'm not sure I'd be up for cutting out 30+ sets x up to 12 classrooms. So, I would probably buy the kits, if I could still find them for $1.20/kit.

- Cut a drinking straw in half.

If you have a bendy straw, cut off the bendy part first. Then cut the rest of the straw into two equal pieces.

## Step 3: Vehicle Assembly 1

- Tape the cut pieces of straw on to the both narrow sides of the vehicle chassis, centering it across the width.
- Insert one end of the coffee stirrer into one of the foam disks.
- Insert the coffee stirrer with a wheel attached already through the already taped drinking straw on the vehicle chassis.
- Insert another wheel on the remaining end of the coffee stirrer.
- Do the same for the other side.

## Step 4: Vehicle Assembly 2

- Cut a drinking straw to your desired length.

If you have a bendy straw, you can decide what to do with the bendy part. Then cut the straw to the length you want. It's up to you to decide which length works for your design.

- Insert a straw into a balloon.
- Put a rubber band around the neck of the balloon over the straw.

DO NOT tie the rubber band too tight. It can collapse the straw, and it won't work well (I've learned from experience).

## Step 5: Vehicle Assembly 3

I decided to create two different designs to see if there's a difference in the distance the vehicle traveled.

- The 1st balloon rocket design has a straight straw piece inserted in the balloon.
- The 2nd balloon rocket design has a bendy straw piece inserted in the balloon.

The 1st balloon rocket design traveled farther with the vehicle than the 2nd.

NOTE: I tried 2nd balloon rocket design with the bendy part up and down, and both positions had problems. Why don't you try it and see what it does?

## Step 6: Lessons-Learned

- As soon as the students started testing their balloon rocket cars, they complained about the wheels coming off completely or their cars curving to the right or the left. I challenged them to come up with a solution to their problem.

Many started with taping the ends of their axel to stop the wheels from coming off, but it didn't stop the wheels from wobbling and not going straight (which was one of the requirements of the project).

- Some complained that their vehicles refused to move, even with a gigantic balloon attached to it.

They had taped the axel (the coffee stirrer) to the axel housing (cut drinking straw), and it couldn't rotate. Therefore, the wheels couldn't rotate, which prevented the vehicles from moving.

- Some students did blow gigantic balloons and learned that BIGGER isn't always BETTER.

Though the vehicles started fast, but they turned upside-down or rolled to one side due to the balloon rocket being too powerful for the vehicle. We tried to weigh down the vehicle, but it didn't work very well.

NOTE: the pictures show some of the solutions for the wheel wobble/wheel coming off issue.

## Step 7: More Air-Powered 1, Incline Surface

This is part 1 of the add-on project I didn't get to do with the class.

- Measure how far a vehicle will travel on flat surface.

- Ramp 1 - Measure how far the same vehicle will travel on this inclined surface.

The plastic tub is 6 inches high, and the ramp is 22 inches long.

- Ramp 2 - Measure how far the same vehicle will travel on this inclined surface.

The plastic tub stack (2 tubs) are 12 inches high, and the ramp is 22 inches long. The steeper descent made the vehicle more unstable, and it crashed into the nearby wall.

## Step 8: More Air-Powered 2, Frictional Forces

This is part 2 of the add-on project I didn't get to do with the class.

- Measure how far a vehicle with travel on flat surface.
- Measure how far the same vehicle will travel on carpet

NOTE: The car on the carpet will not travel as far as the car on the smooth surface. The difference in the distance traveled is the force lost due to friction.

## Step 9: Science Behind This Activity

I love Newton's Second Law, because it's easy for people to understand.

**Force = Mass x Acceleration**.

I use this all the time when I do projects with students. Whether it's a kindergarten class or a sixth-grade class, I write F = ma on the whiteboard and explain the relationship between them.

__On flat surface (1st diagram):__** F = ma ****= F (Balloon) - F (Ground friction)**

- The total of all the forces acting on our vehicle will result in acceleration.
- How fast the vehicle will accelerate will depend on the size of the force acting on the vehicle.
- When the air in the balloon is pushed out of the straw through the back, the balloon is pushed forward. When the balloon is pushed forward and is taped to the vehicle, the vehicle moves forward with the balloon.

Actually, F=ma is too simple. What it really means is that F = ma = F (Balloon) - F (Ground friction). But in most cases, we assume F (Ground friction/Resistance) = 0 on smooth surfaces because it's very, very small.

__On a ramp (2nd diagram):__** F = ma = [F(Normal) - F(GravityY)] + [F(Balloon) + F(GravityX) - F(Ground friction)]**

- The total of all the forces acting on our vehicle will result in acceleration.
- How fast the vehicle will accelerate will depend on the size of the force acting on the vehicle.
- When the air in the balloon is pushed out of the straw through the back, the balloon is pushed forward. When the balloon is pushed forward and is taped to the vehicle, the vehicle moves forward with the balloon.

If the ramp is smooth, F (Ground friction) = 0, too. F (Ground friction) depends the smoothness of the surfaces, not the angle of inclination. And conveniently, [F(Normal) - F(GravityY)] = 0, because they are equal and opposite forces.

So, the long equation is shortened to F = ma = [F(Balloon) + F(GravityX)].

NOTE 1:

In kindergarten, I use addition/subtraction to get them to understand the relationship between the three. If F is constant, and m is big, a is little and vice versa.

NOTE 2:

If you want to solve for F(GravityX), the mathematical equation is

F(GravityX) = F(Gravity) x sine(angle).

If you want to solve for F(GravityY), the mathematical equation is

F(GravityY) = F(Gravity) x cosine(angle).

NOTE 3:

In __More Air-Powered 2, Frictional Forces__, F(Ground Friction) is not 0.

The car on the carpet will not travel as far as the car on the smooth surface.

The difference in the distance traveled is the force lost due to friction.

## Discussions