PhysicsLAB: Foil Barge

In this lab we will investigate the buoyant force on a 36 in² piece of aluminum foil Our method will be to build a foil barge and determine the maximum number of pennies it can hold without sinking.

I. Constructing your barge

First, fold your 6 inch x 6 inch piece of aluminum foil into a rectangular "barge." As you fold, be very careful not to rip the foil, making all of the "walls" the same height, and sealing all of the corners..

image courtesy of TeaWithBuzz

Once the barge has been constructed, measure in centimeters the length and width of its base and the height of its walls to one decimal place.

What is the width of the base of your barge in cm?

What is the length of the base of your barge in cm?

What is the area of the base of your barge in cm²?

What was the average height of your barge's "walls" in cm?

What maximum volume of water (in cm³) could your barge displace if, when filled with pennies, it remains floating when the water level just reaches the tops of its walls?

We have studied that the buoyant force on a object is equal to the weight of the water that it displaces.

What is the density of the water from your local water source in kg/m³?

Based on your previous answer for the barge's volume, what will be the maximum buoyant force supplied by the water? Give your answer in newtons.

II. Determining the average mass of a penny

Next you need to determine the average mass of a single penny so that you can predict the maximum number of pennies that can be placed in your barge without it sinking.

Count out 50 pennies and measure their mass to the nearest 10^th of a gram.

What is the weight of a single penny in newtons?

Based on the buoyant force calculated earlier, what is the maximum number of pennies your barge can hold?

III. Testing

Count out your predicted number of pennies and carefully place your barge in the water tub. Make sure that the barge has NO contact with the walls of the tub or its base.

Slowly begin placing your pennies. Remember to keep the barge balanced and the pennies symmetrical. Keep going until you feel that no more pennies can be safely added to the barge. If you have exceeded your predicted number, you may get additional pennies.

Once you stop adding pennies, your barge must float for a minimum of 60 seconds. If the barge sinks on the 59th second, it is disqualified, the same as if it sank on any earlier second. After you have completed your timing, you may NOT add any additional pennies.

Remove your barge from the water tub and set your pennies out to dry.

IV. Conclusions

Was your barge still floating at the end of 60 seconds?

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How many pennies did you place in your barge?

If the final number of pennies did not agree with your predicted value, explain why. Or if your barge sank before the predicted number of pennies had been added, explain why.