Putt Putt Boats

Introduction

Light a small candle inside a toy boat and watch it coast around the water while making a “putt putt” noise. Use this old-fashioned toy to illustrate how chemical energy is converted into mechanical energy as phase changes occur.

Concepts

• Chemical energy
• Force and motion
• Phase changes

Materials

Safety Precautions

Use extreme care while working with an open flame. The boats get very hot. Do not allow students to touch the boats while they are in motion. Do not remove boats from the water until the flame has been extinguished and the boats have cooled for at least five minutes. Exercise caution when inserting glass tubing during follow-up demonstration. Use glycerol to lubricate the glass and wear protective gloves. Please follow all other normal laboratory safety procedures. Wash hands thoroughly with soap and water before leaving the laboratory.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. Putt Putt Boats may be reused many times. Dry off the boats after use to prevent rusting. Candle remains which have solidified may be thrown away in the trash.

Procedure

1. Fill the water basin to a depth of 3–4 cm with water.
2. Use the small pipet to fill one of the pipes in the rear of the boat with water until water comes out the other side (this indicates that the pipes and water tank are filled) (see Figure 1).
3. Cover the pipes with your finger to keep the water from spilling and place the boat in the water basin.
4. Place a candle in the tin candle holder and light the candle while holding the end.
5. Place the candle holder inside the boat so that the flame is underneath the water tank (this is as far inside as the candle will go) (see Figure 2).
6. Within a minute the boat will begin to make noise and move around the basin.

Alternative or follow-up teacher demonstration to illustrate what is occurring inside the boat

1. Insert the glass tubing into the stopper until the tubing is within one cm of the bottom of the test tube. Use caution when inserting glass tubing. Glycerol should be used to lubricate the glass. Wear protective gloves.
2. Remove the stopper and fill the test tube completely with water.
3. Stopper the test tube.
4. Clamp the test tube stopper-side down (towards the tabletop) and secure the clamp to a ring stand. Adjust the height of the test tube so that a Bunsen burner will fit underneath the rounded end (see Figure 3).
5. Submerge the glass tubing into a large, wide-mouthed bowl filled with 2–3 inches of water.
6. Set up a Bunsen burner under the rounded end of the test tube.
7. Place a putt putt boat (without a candle) into the water.
8. Light the Bunsen burner and make sure the flame is heating the bottom of the tube.
9. After a minute or two the water above the flame will begin to boil. This will force water to spurt out of the glass tubing into the water dish.
10. The glass tube will momentarily fill with steam, which will quickly condense as it is cooled due to the surrounding water. This will draw water from the dish back up into the rounded end of the test tube, and again the water will boil (see Figure 4).

11. Steps 9 and 10 will occur over and over in quick succession, making a noise similar to the putt putt boats. The spurting out and sucking up of water from the bowl into the glass tubing will cause the water in the dish to shift, which will in turn propel the boat around the dish.

Teacher Tips

• {12648_Tips_Figure_5}

  A water basin may be constructed using four 2 x 4 boards, each at least 70 cm long, 8 long nails, and a large, heavy-duty garbage bag. Use nails to construct a square frame from the 2 x 4s (see Figure 5). Place the frame inside a large garbage bag. If the bag is not large enough, cut along the side and across the bottom seam and drape the bag over the frame (check for tears in the plastic bag). Fill with a few centimeters of water.

• Each boat comes with an oil wick for creating an alternative heat source. We found that using candles rather than oil works better and is less messy.
• This activity pairs nicely with a steam engine demonstration such as the Hero’s Engine Kit available from Flinn Scientific (Catalog No. AP5717).

Further Extensions

• Follow the basic procedure, only this time measure and record the temperature of the water in the basin after completing step 3.
• Set up the boat(s) and let them warm up. After they begin to run at a steady pace, have students count the number of putts the boat produces in a 15-second period. This can be difficult—it may be as many as five putts per second. It may be easiest for students to tap a pencil on a sheet of paper along with the sound of the putts and count the dots after time is called. Alternatively students may count every second “putt” and then multiply by two. Divide the number of putts counted by the total time, 15 seconds, to find the average number of putts per second.

Example: 72 putts/15 seconds = 4.8 putts per second

• A rough estimate of the amount of water vaporized per putt is around 1% of the total mass contained in the water tank and pipes. Have students mass the water in the tank and pipes. Fill the tank and pipes completely with water and pour it out into a small beaker. Set on a balance that has been zeroed to the weight of the beaker so that only the weight of the water will be measured. The weight of water in grams approximately equals the milliliters of water in the tank and pipes. Multiply the milliliters of water in the tank by 0.01 to find the estimated amount of water vaporized per putt.

Example: 1.28 mL x 0.01 ≈ 0.013 mL

Have students estimate the horsepower (energy transferred per second) of a putt putt boat. The heat energy is calculated using the following formula:

where 

m is the mass of water vaporized per putt 

c is the specific heat of water (4.18 J/g•C) 

ΔT is the change in water temperature from initial temperature to 100 °C (boiling)

ΔH is the heat of vaporization of water (2260 J/g) 

Q is the heat energy

Example (assume the initial water temperature was 20 °C before running the putt putt boat.):

[(0.013 g) x (4.18 J/g•°C) x (100 °C – 20 °C)] + [(2260 J/g) x (0.013 g)] = Q = 34 J

A watt is equal to a joule per second. Therefore, 34 J per putt multiplied by 4.8 putts per second is equal to 163 joules per second, or 163 watts. One horsepower is equal to 746 watts. Each boat produces about 0.22 horsepower (163 watts/746 watts/horsepower). These values are simplified calculations but are useful for estimating an approximate horsepower of the boat.

• The total water displacement of the boat can be determined using the following procedure.

1. 1. Place the boat without the candle or candleholder in a bowl approximately ⅔ full of water.
   2. Add coins one at a time to the inside of the boat.

Note: Surface tension between water molecules may be observed around the edges of the boat as it gets close to sinking. The boat will go slightly below the water level without breaking the surface tension. The water will appear to bend down towards the edges of the boat. Adding additional weight will eventually break the surface tension, and water will enter the boat.

• 3. Continue adding coins until the boat sinks.
  4. Remove the boat and the coins from the water and dry them off.
  5. Count how many of each coin are present and calculate the total weight of the coins and the boat using the following information. If time allows, have students weigh the boat and coins for more accurate results since weight values may vary slightly. (Make sure they are dry first.)

Boat ≈ 33.0 grams
Quarter ≈ 5.6 grams
Nickel ≈ 5.0 grams
Dime ≈ 2.2 grams

The total weight of the boat and coins that sunk equals the weight of the water displaced by the boat. Water weighs 997.8 grams per liter at 25 °C, so the liters of water displaced can be calculated using the formula:

As a practical application, these types of calculations must be considered in order to figure out engine size and load capacity for steam engines.

Discussion

The rapid-fire, putt putt noise produced by the boat is the result of water spurting out and being sucked (or better, pushed) back into the “exhaust pipes” and into the water tank. The water tank is located directly above the flame on the inside of the boat. As the flame heats the tank, the water boils, forcing water out the back pipes as the molecules move more rapidly and spread out. The steam trapped in the pipes will condense as it is cooled by the water surrounding the pipes, resulting in cool water from the basin being drawn back up into the pipes and chamber. The water will again boil and the cycle will start over again. This cycle occurs over and over in rapid succession, causing the boat to move about. The erratic motions of the boat are due to unequal amounts of water spurting out of the two exhaust pipes. For example, if a larger amount of water shoots out of the left hand pipe, this will force the boat to move to the right, and vice versa. The boats are designed to utilize the energy produced as the phase of water changes from liquid to gas and back to liquid. The alternative or follow-up procedure illustrates the phase changes occurring inside the boat in a clear tube so that students can view what is happening.

References

Holdings, Bernie; The Putt Putt Boats Science of Steamboats Instructor’s Guide; Higart Holdings: Everson, WA, 2001.