Balance scales are a tool used to concretely teach children about weights and equivalency measures. Exploring and seeing the concept in action will impress the principles on their minds better than more passive activities or worksheets.
Weight Versus Size
The very first concept to teach with a balance scale is the simple idea that bigger often means heavier. A hands-on method for doing this is to use lumps of clay or play-dough. Have the children put various sized pieces of the material on either side of the scale and see which one pulls down its side of the scale, showing it is heavier. As a forerunner to a later activity, have them attempt to put two pieces on the scale that are the exact same size, balancing the scale. This lays the groundwork for the idea of estimation.
Variations in Mass
The next concept for which you can use a balance scale is that of varying weights despite relative size. The easiest way to do this is to gather 5 to 10 small objects that are known to be particularly heavy or light for their size. Some examples are a large handful of cotton balls, a lead ball, a pencil, an eraser, several feathers, a couple of index cards, a block magnet or even a snack baggie with a zipper closure with water in it. (Double bag the water as a precaution.) Have the students put an item on each side of the scale to see which is heavier. Students can put the items on a chart showing comparisons. Younger students may need a worksheet prepared with pictures to compare their findings.
The next idea to explore is estimation. Use dried beans or other "counters". Start by putting an unknown number of beans on one side of the scale. (Use enough that students cannot easily count them just by looking.) Have students take turns trying to guess (estimate) the number of beans. Check their guess by counting out that many beans into the other side to see if the scale balances.
Introduce the concept of weight measurement by again using the beans and the items from the first activity. Put an item on one side of the scale and have the students count how many beans it takes to balance the scales. They can write their answers on a simple chart. Repeat this exercise with several different items.
Once the students are familiar with the scales and concepts of varying weights, begin using the scales to teach mathematical functions like addition and subtraction. Show them how to put a number of beans on one side of the balance and a lesser number on the other. See how many beans have to be added to the smaller side to balance (equal) the first side. In the same way, they can subtract beans from the first amount to get it to balance the lesser amount. Have them write each transaction as an equation.
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