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Steam Propulsion

Steam Propulsion

Introduction: (Initial Observation)

You may have noticed that the steam from boiling water can lift the lid of a pan. The pressure of steam lifts the lid, some steam exits, pressure reduces and the lid comes back down. Many of such observations created the idea of using steam power to do other works such as powering a boat or a car.

The very first self-propelled car was built in 1769, when Nicolas Cugnot, a French military engineer designed a steam powered road-vehicle.

The vehicle was built at the Paris Arsenal, and was used by the French Army to move cannons. It had three wheels with the engine in the front along with the boiler. While Cugnot’s ‘car’ was capable of attaining speeds of up to 6 kms/hour, it was far too heavy and slow to be of practical use. Since then many other inventors have successfully and commercially used the power of steam to run boats, cars, trains, machineries and electrical generators. In this project you will display simple methods that can use steam and convert heat energy to mechanical energy. You may even build a steam propelled boat or car.

If you are required to work on an experimental project, you will also need to have a question, a hypothesis, experiment results and possibly a graph. The question that will be studied in this project guide is:

How does the nozzle size affect the efficiency of a steam propelled vehicle?

This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Gather information about steam propulsion machines. Read books, magazines or ask professionals who might know in order to learn about the use of steam as a driving force or a source of mechanical force. Keep track of where you got your information from. Following are samples of information that you may find:

Mechanical Energy from Steam:

When you heat a gas like air or steam, the molecules in the gas move around faster. The faster they move, the harder they hit anything that is in the way. If we put something in the way, such as a propeller or a pinwheel, we can make them spin (this is how turbine generators spin to create electricity). If we confine the gas in a container with a lid, we can pop the lid off (this is how the engine in a car works). If we let the fast moving molecules push on one side of a container, and escape through a small hole on the other side (so they are pushing on one side more than on the other) then we have a rocket or a jet, which moves in a direction away from the side with the hole.

Hero’s steam engine.
In the first century AD, the mathematician Hero of Alexandria described a device called the aeolipile, in which steam was conducted through pipes from a boiler to a sphere which had two jets from which the steam could escape.
This simple machine provided the idea for invention of turbine during the Industrial Revolution.

Now modern turbines power most of the world’s ships and power plants. Related to steam turbines are gas and water turbines.

The Steam Wagon

In 1687 Isaac Newton attempted to put his newly formulated laws of motion to the test with his “steam wagon”. He tried to propel the wagon by directing steam through a nozzle pointed rearward Steam was produced by a boiler mounted on the wagon. Due to lack of power from the steam, this vehicle didn’t operate.

This is a model of Aeolipile made of copper.

The Pop-Pop Boat

Often toys can be found that employ simple physics principles in ingenious ways. Such ones are favorites for demonstration lectures: they get attention as well as teaching the physics. But toys for that purpose get hard to find as more and more of them operate with hidden solid-state chips. For the one for this column, I’m safe from chips, because it’s a hundred years old. The toy is a jet-propelled boat, Fig. 1.1 Heat from a small candle inside it makes it eject pulses of water from tubes at the rear just under the water level, at five or more per second. That propels the boat at 10 cm/s or more, and it will go for as long as the candle burns.

The boat was invented and patented by an English engineer in 1897. Since then numerous articles2 have been written about it and it has been manufactured and sold in several different countries, under the names Pop-Pop, Put-Put, Toc-Toc, and Puf-Puf. There even is a society for it.3 I am indebted to William Mundus of Ann Arbor, for the loan of all the literature in Ref. 2. Interesting, but after reading it, I, as Omar Khayyam wrote in the eleventh century, “came out by the same door where in I went”. At least so far as finding out how it really worked. So then I started on my own, with “reverse engineering” (Fig. 2).

Inspection of simple tests answered several questions.

  1. Priming. Two pipes run from the heated chamber (boiler) to exit at the back of the boat. Why two? The system must be primed before the heat is applied, by putting water into an exit tube. It will go in only if air can come out. That the second pipe serves no other purpose was shown by plugging it after the system was primed and running. The pulsing went on.
  2. Gravity. As the boat sits in the water, the two pipes have a downward slant Boer turning up to the boiler. While the motor was running, I topped the boat up to 45 degrees, keeping the exits of the pipes under water. Put-putting continued. This showed that, whatever the water does, pressure changes in the boiler must be more important in moving it than gravity is.
  3. Temperature of the pipes. After running a minute the heater tray was removed quickly and the pipes were felt with a finger. They were cool up to where they started to bend upward, then too hot for the finger. That showed that live steam may get into the bend but not further.
  4. A puzzling question was the origin of the put-put sound. It comes from the top cover of the boiler, which acts as a diaphragm. It is very thin (0.002 in. or 0.05 mm) hard copper. It would be able to make a pop only by a very sudden movement. It was suggested in the book by Harley2 that the copper is slightly concave or convex, so that with a little change in pressure it reverses, with a pop. Like the bottom of an oil can. Easy to test. I applied gentle air pressure and suction, by mouth, through the exit pipes. The pops were identical to those heard from the operating boat. Suction proved to be unnecessary: the diaphragm returned itself after being forced out. However, as will come out later, there probably is suction at some part of the cycle.

To go further, it seemed necessary to see what goes on inside the boiler. The top cover of the boat was

removed (with some difficulty), and the diaphragm of the boiler was cut away. The top of the boiler was then closed by a piece of 1/8-in. (3 mm) thick Plexiglas, cemented on with epoxy. When the boat was “fired up” it operated normally, except silently. That showed, first, that the movement of the diaphragm played no necessary part in the oscillation of the system. Throughout the operation, the boiler contained a little water, but at least 3/4 of the area was dry — and presumably hotter than the boiling point of water. That showed, second, that the water expelled in the pulses at the rear of the boat is not supplied from the water put in for priming. It means that between the pulses out, water must be sucked into the pipes to replace that expelled.

We now begin to piece together the oscillation cycle. The following is my speculation. Start when there is reduced pressure in the boiler and water is being sucked up in the pipes. A little goes onto a hot surface in the boiler and flash-vaporizes. Resulting steam pressure forces water down the pipes, giving the boat the propelling pulse. The steam quickly condenses in the cooler parts of the system, mainly the boiler, reducing the pressure so that water is sucked up again, some of which goes onto a hot surface and starts the next cycle. It’s a typical relaxation oscillation, of which there are many examples.4 So that’s my picture of what happens.

You may question very logically how, if water is expelled and sucked in alternately, there can be a net force forward to make the boat go. In the past I spent time puzzling a similar problem. It started with a question posed by Richard Feynman in 19855 about the familiar whirling lawn sprinkler. His question: if the sprinkler is submerged in water, and water is sucked into it instead of being squirted out, will it rotate in the same or opposite sense? (Evidently he assumed it would rotate.) I did the experiment, and couldn’t get rotation either way. Feynman’s question started a firestorm of letters and articles that didn’t peter out until the early ’90’s. As I remember, the end was quiet, with no agreement.

While the Put-Put is not exactly like the sprinkler, the answer in simplified form may apply to both. It is that as water is drawn into any closed container, there is an exchange of momentum between container and water, giving a forward force on the container. But as soon as water is inside, it has to stop, with the opposite exchange of momentum. So the container gains or loses no momentum. There may be a small displacement, while the water is in motion, but there is no residual velocity. Not so if the container is squirting water out. It gives momentum to the water, gaining the opposite itself, but the water is gone, to the outside: the water does not make the opposite exchange with the container. We know that the system propels, or we would not have gotten to the moon. Just rocket action. So the Put-Put boat does go forward.

Even when you believe the theory, it is well to be reassured by an experiment. With the squeeze bulb of a battery filler syringe from an auto supply store, I rigged up a demonstration. (It might be interesting in a lecture.) The rubber bulb was held collapsed by a string harness. it was mounted on a wood raft, floated in a sink full of water, with the open end of the tube under water. When quiet, the string was burned, letting the bulb expand and suck up water. There was a very small displacement, as mentioned above, but the raft had no residual velocity.

The above suggests one answer to a problem known to physics classes. If you are marooned on ice that has (hypothetically) zero friction, how do you get off? By the method of the Put-Put, if you would just breathe in and out, facing in one direction, you would propel yourself. And with zero friction, your speed would be cumulative.


  1. Purchased from Brainstorms, 1996 winter ed., 8221 Kimball, Skokie, IL 60076-2956; 1-800-231-6000. $14.85 (Made in China).
  2. Two sources were informative: Derek Pratt, Model Engineer 176, 53-55 (Jan. 5-18, 1996), a magazine published by Nexus Special Interests Ltd., Hertfordshire HP2 7ST, England, and discussion in Toyshop Steam, by Basil Harley (Argus Books, 14 St. James Rd., Watford, England, 1978), pp. 45-48. There are seven letters from readers in Model Engineer in 1996: Vol. 176, p. 384; Vol. 177, pp. 374-375; and Vol. 177, p. 616. A bibliography on Pop-Pop boats exists in the editorial office of Model Engineer.
  3. In France l’Asso. des Amateurs de Moteurs Pop-Pop, organized in 1992, has 200 members.
  4. How Things Work “What does the drinking bird know about jet lag?” Phys. Teach. 27, 470-472 (Sept. 1989).
  5. Richard Feynman and Ralph Leighton, Surely You’re Joking, Mr. Feynman (Bantam Books paperback edition, 1985), pp. 51-52.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

Newton’s steam wagon did not work at all. In theory, the pressure of steam that exits from the back, must push the wagon forward. So why Newton’s wagon did not work?

I am wondering if the nozzle (where steam exits) in Newton’s wagon was too big. A big nozzle allows the steam to exit easily with no pressure. The purpose of this project is to determine if the size of nozzle affects the efficiency of a Newton wagon (or any similar boat or car).

How does the nozzle size affect the efficiency of a steam propelled vehicle?

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

  • The independent variable is the size of nozzle.
  • Dependent variable is the distance a model car (or boat) travels per minute.
  • Controlled variables is the air temperature.
  • Constants are the type of fuel, the amount of fuel, size of boiler, size and shape of vehicle (boat or car).


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

My hypothesis is that the size of nozzle affects the efficiency of a steam propelled car. A very small nozzle or an oversize nozzle do not create enough push to drive the vehicle.

My hypothesis is based on my observations of air filled balloons that fly away if you open their mouth. Such balloons do not fly away if they have a very small hole in them.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:   Make a steam propelled boat (or car)

Introduction: Any metal can can be used as a boiler in order to construct a model of Newton’s wagon. Following is just a sample procedure. You need to adjust this procedure based on the materials that are available to you.


  • Metal tube (a cigar tube works great — ask an adult to get you one)
  • Two pieces of metal strip that can be used to secure the tube on the boat
  • Four screws for connecting metal strips to the boat
  • Cork that fits snuggly into the end of the tube
  • Two food warmer candles (in metal cups)
  • Wood blocks or steps (4 inch by 8 inch, 1/2-inch thick)
  • 2 wooden pieces (4″ by 2″, 1″ thick)
  • Masking tape
  • Hammer and three nails
  • Matches, Screw drivers

You’ll need an adult’s help with the matches and the hammer and nails!


  1. Put the cork into the end of the metal tube making sure its very tight. Carefully poke a small hole through the cork with a nail.

2.Cut a boat shape out of the balsa wood, making a triangle bow in one end. Hammer two large nails in each end about one inch in from each end. The nails will help to stabilize the boat.

3.Attach two wooden steps on the top of the boat to create an elevated area for holding the tube.

4.Mount the two candles about 1-1/2 inches from each end of the wood. Use loops of masking tape to stick the metal cups to the wood.

5.Use the metal strips to mount the tube over the candles. Wooden steps will hold the tube just above the candles. Wrap the ends of the wire around and under the board and twist the ends neatly on the underside. (See picture.)

6.Carefully remove the cork from the tube and fill the tube about one-quarter full with very hot water. Tightly replace the cork. Make sure water will drip out the hole in the tube.

7.Fill up a bath tub or a large sink with water.

8.Put your boat in the water and ask an adult to carefully light the candles.


The heat of the candle will cause the water in the tube to boil. The water will change to steam and the steam will escape out the hole in the cork pushing the boat forward in the water.

Here are some questions to think about:

  • Why use hot water in the tube?
  • What would happen if you used cold water?
  • What would happen if you didn’t put a hole in the cork? (DON’T TRY THIS!)
  • What would happen if the hole in the cork were larger?

What’s Happening

There are two different things to learn here.

The first is what makes rockets fly off into space. It’s a law of physics that says “for every action there is an equal and opposite reaction.” What this means is that the steam escaping out the hole in the cork is an action in one direction. The reaction is that the escaping steam will push the boat forward.

A rocket works the same way. Hot gases and fire come out of the motor of a rocket. The gases coming out the nozzle at the bottom of the rocket come out in one direction. These escaping gases push the rocket in the opposite direction.

Second, energy from the candles changes the water into a gas (water vapor or steam). The steam can escape Steam is used in a lot of energy power plants.

The heat of the candle will cause the water in the tube to boil. The water will change to steam and the steam will escape out the hole in the cork pushing the boat forward in the water.

Experiment 2: Effect of nozzle size on the efficiency or speed of a steam propelled vehicle?

In this experiment you will make three identical steam propelled boats with three different nozzle sizes. Place them in water and light on the candles. You may either compare the speed of each vehicle or you may measure and record the total distance that each boat can travel before it runs out of water or fuel. (Note that all three boats will have the same amount of water and fuel).

Note that you have verities of choices in designing the boat, selecting the tank and selecting the hear source. You will not have to use the design suggested above.

Materials and Equipment:

  • Metal tube (a cigar tube works great — ask an adult to get you one)
  • Two pieces of metal strip that can be used to secure the tube on the boat
  • Four screws for connecting metal strips to the boat
  • Cork that fits snuggly into the end of the tube
  • Two food warmer candles (in metal cups)
  • Wood blocks or steps (4 inch by 8 inch, 1/2-inch thick)
  • 2 wooden pieces (4″ by 2″, 1″ thick)
  • Masking tape
  • Hammer and three nails
  • Matches, Screw drivers

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.



Summery of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.