## Just How Thick Is Aluminum Foil?

This activity is a perfect way to get students to practice using significant digits in the laboratory. The idea is that each lab group will be given a small rectangular piece of aluminum foil, a centimeter ruler, and access to a balance. That's all the set-up required! A science teacher's dream!

Explain to the class that they will be measuring the thickness of a piece of aluminum foil, but that it cannot be done with a traditional ruler because the foil is just too thin.

## How to Find the Answer

Have students brainstorm possible methods for solving this problem.

Tell the class that one possible way to solve the problem is use the density of aluminum, which is 2.70 g/ml. If you know this, as well as the mass of the aluminum piece and the formula for density (D= mass/volume), you can solve the formula for the volume of the piece of aluminum foil.

Once you have calculated the volume of the foil you may then use the formula for the volume of a box, which is V = length x width x height. It is easy to measure the length and width of the foil using the centimeter ruler. Substitute the values into the volume formula and solve for the height. This represents the thickness of the aluminum foil.

## Incorporating Sig Digs

In addition to practicing density calculations and measuring techniques, this activity provides a great opportunity for significant digits practice.

First, it is necessary to help students understand how to read their centimeter rulers. (In other words, what decimal place can the rulers read to?) Secondly, direct students to count the number of signifcant digits in their measurements. Third, remind them that they need to round their multiplication and division calculations to match the number of significant digits in their original measurements.

## Activity

Cut and paste this article into a word-processing document. Add or remove items to vary the level of inquiry you would like in your classroom.

Name____________________________________ Hr_______ Date_______________

Objective: Determine the thickness of aluminum foil using mass, length and width measurements as well as the density of Al.

Materials:

- rectangular piece of aluminum foil
- balance
- centimeter ruler

## Measurements

Find the mass of your aluminum foil. (mass = __________ grams)

Measure the length and width of your aluminum foil.

(Remember to record all numbers that you know for sure plus one estimated digit.) (length = ______ cm and width = _________ cm)

## Calculations

Calculate the volume of your aluminum piece.

Use the density formula, D = mass/volume for this. Solving for V gives

V = mass / density

(Volume of foil = ________ cubic centimeters = ______ ml)

Note: 1 cubic centimeter occupies the same volume as 1 milliliter.

Round your answer to match the origincal measurement that had the fewest significant digits.

(Volume after rounding for significant digits = _________________ ml)

Calculate the thickness of your aluminum.

Use the formula of a box, V = length x width x height

solve the formula for height, which represents the thickness of the aluminum foil in cm.

(h = _______________ cm thick)

Round your answer to match the original measurement with the fewest significant digits.

(Thickness after rounding significant digits = __________________ cm.)

## Questions

- Why couldn't you use a centimeter ruler to measure the thickness of the aluminum foil?
- What would you say to a person that recorded the length of her aluminum foil as 3.4575 cm after measuring with a ruler marked to the nearest millimeter?
- Why do scientists use significant figures when taking measurements and doing calculations in the laboratory?
- When is one time that a number is exempt from the use of significant digits?
- Write a one paragraph summary of this activity and your findings.

## Interesting Tidbit

Some places that manufacture paper and aluminum foil actually test the thickness of their product by shining a beam of radioactive particles at it. The more particles that pass through, the thinner the paper. This is how = a simple geiger counter or radiation detector can be turned into a quality control device. Who knew?!