Module 3
Planning Guide

Lab 1.11

Lesson 1.9
Lesson 1.10
Lesson 1.11
Lesson 1.12
Lab 1.9
Lab 1.10
Lab 1.11
Lab 1.12
Project 3

Physics Lab 1.11 Soda Bottle Rocket

Soda bottle rockets provide an extremely effective way of illustrating the power of reaction or conservation of momentum. By accelerating a mass of water away from itself, the rocket has to gain momentum equal to the momentum gained by the water in the opposite direction. Some of the water travels with the rocket before it can leave the bottle and there is therefore an optimum amount of water that provides the maximum height that can be achieved by the rocket.

There are also a number of different designs for soda bottle rockets that can be used and there is much fun to be had in building and launching these rockets.

Note: Read the SAFETY INSTRUCTIONS before attempting to launch a soda bottle (or water) rocket.

Design and build your own rocket and launching device or purchase a launching clamp from one of the suppliers listed in the Laboratory Handbook.

Carry out the experiments described below and record the results in the table provided.

1. A soda bottle with a mass of 100g is traveling at 8 m/s. What is its momentum?
2. A water rocket shoots out 200g of water as it takes off. During this time, the average velocity of the water is 6 m/s. If the mass of the bottle/rocket is 100 g, what is it’s velocity during take-off?

Experiment 1.11.1 Soda Bottle Rocket

The purpose of this experiment is to determine the effect that the amount of water used in a soda bottle rocket has on the maximum height of the rocket.

Safety Instructions:

1. Aim the rocket only in such a way that it will land in an open space away from people, motor vehicles, power lines or buildings.
2. Wear safety glasses or goggles while within a distance of 3 meters from the pressurized rocket.
3. Keep a distance of at least 2 meters while the rocket is being pressurized.
4. Launch rockets vertically. Take note of the wind direction.
5. Bear in mind that rockets with tail fins, nose cones or any other additional devices will probably come down nose-first and strike the ground with much more force than an empty soda bottle.

Materials and Equipment

• Empty 2 liter polyester soda bottle
• Stopper and clamp
• Plastic tubing
• Valve
• Pump
• 3 dowels or strips of wood

Procedure

1. Assemble the launching device.
2. Three dowels hammered into the ground around the launcher can serve as a crude guidance system.
3. Experiment with different quantities of air and water to determine the optimum combination of pump strokes and water to achieve the maximum height.

Calculations

Judging the height of the rocket could be simplified by standing a known distance away from the launching point and measuring the angle of a line to the rocket when it reaches its maximum height.

A simple device to assist with this task is a large protractor with a small weight hanging on a piece of string from its origin point. Sight the rocket along the straight edge of the protractor and clamp the string against the protractor when the maximum height is reached. The angle between 90º and where the string is clamped is equivalent to the angle between the horizontal and the line to the rocket.

The tan of this angle = height of rocket / distance from launching point.

Results

Use the table to record the results of the different experiments and determine the optimum combination of water and air pressure

1. 0.1 kg x 8 m/s = 0.8 kg-m/s
2. Momentum of water = 0.2 kg x 6 m/s = 0.12 kg-m/s = momentum of rocket in other direction.
   Momentum of rocket = 0.1 kg x velocity = 0.12 kg-m/s
   Velocity = 0.12 / 0.1 = 1.2 m/s.