Money Scales

by littleBits

Published on April 3, 2012

Are objects worth as much as they weigh? In this activity, your students will build a simple circuit with littleBits modules to investigate this question. The lesson helps students practice money and measurement skills as well as apply problem-solving skills in an interesting, unordinary way.


Students will be able to:

  • Build a circuit with littleBits modules to compare masses of objects

  • Accurately determine the value of different sets of coins

  • Record results in a data table

  • Discuss variables affecting the results of different student groups


Use the attached checklist to assess your students’ ability to attain the objectives of the lesson. The checklist can be used as a self-assessment tool by students and/or as a teacher assessment tool.


Common Core Math Standards

  • MD:  Measurement & Data

Common Core ELA Standards

  • SL: Speaking & Listening

Next Generation Science Standards

  • PS3: Energy

  • ETS1: Engineering design

Duration: 1 day, 45 minute class

Lesson Guide


Introduce the activity

Start by introducing the idiom, “worth its weight in gold.” Ask students to describe the meaning of the phrase. If time allows, give students time to conduct their own online research to reinforce their understanding of the phrase. You may also consider discussing the origin of the phrase as shared here from the American Museum of Natural History:


Many students may also be familiar with the phrase, “worth their salt.” Explain that the two phrases are practically synonymous.

Tell students that today they will set up a circuit to test whether or not items are worth as much as they weigh. The difference is instead of using gold they will use spare change.


Build the circuit

Distribute the necessary littleBits modules to balanced student groups. Based on their level of familiarity with the modules, you may need to provide some background information on individual modules and allow time for free exploration.

Ask students to connect the modules in the following order: power, pressure sensor, wire, bargraph. When done, the circuits should look like the one in the picture.
Img 20150804 135902

Picture 2


Explore the pressure sensor Ask students to look at the pressure sensor. It has the same function as a light dimmer, except for instead of twisting the knob to change the flow of electricity, you apply pressure to the sensor. The greater the pressure, the more electricity will flow through the circuit. Give students time to explore the pressure sensor in their circuits.
Img 20150804 135928


Add a thin cardboard circle

The tricky thing about using the pressure sensor as a scale for weighing objects is that the black rim around the edge of the pad is not pressure sensitive (only the inner part with the golden lines detects the pressure). Therefore, if you put something flat directly on it and try to weigh it, you might have trouble detecting the resulting pressure.

As a work around, ask students to cut a small circle out of a thin cardboard and tape it to the pressure sensor. Make sure that the circle is not so small that coins will wobble and fall off, but also make sure it is small enough so that it rests completely inside the the black ring.
Img 20150804 135951


Set-up the money scales

Students should lay their circuit flat and bend the pressure sensor back so that the pad is resting on a book or other hard surface.

Have students turn on their circuits by flipping the switch on the power module to the “on” position, and slowly start to stack coins onto the center of the pressure sensor. When the first light on the LED bargraph lights up and remains lit without flickering, ask students to note how many coins are on the scale. Students should also note the value of the coins in the stack. Student groups can create their own data tables or use the data table attached to the lesson.

Students should keep adding coins until the second light turns on. Again, have students note the number and value of coins on the scale.

Students continue to add coins and note the number and value of coins on the scale as each light on the LED graph is illuminated.

Note that the value of the coins the students choose to stack on their money scale will affect the value of their stacks. For example a stack of pennies will not have the same value as a stack of quarters of the same weight. You can choose to standardize this variable or allow students to discover how this affects their scale through investigation and discussion.
Img 20150804 140024


Weigh trinkets

Now that students have normalized their scale and know how much certain weights are worth, they can use their number scales to investigate the value of objects around the room.

Ask students to weigh an object and note how many lights on the LED graph show up. Approximately how much does this object cost based on its weight? Would they pay that amount of money for that object?

Have students continue to weigh various trinkets and classroom objects. Consider setting up a trinket supply of small objects for students to weigh. This can help encourage student groups to weigh similar objects so the class can easily compare the results from different money scales in discussion. When setting up your trinket supply, select medium weight objects. You may have to play around with this to find a few good ones.

Can students find one object that is worth more than its weight and one that is worth less than its weight? Are there any that they think are worth exactly their weight?

How do the coins students chose to calibrate their scale affect the value of the objects they weighed?