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E2.4 compare, estimate, and measure the mass of various objects, using a pan balance and non-standard units
Key Concepts:
The unit chosen for a measurement affects the numerical value of the measurement; if you use a bigger unit, fewer units are required.
The mass of an object tells how heavy it is. A big object can have a smaller mass than a smaller object.
Be able to measure objects using non-standard units. They will then explore reasons to use standard units.
Before measuring, ensure that the two pans on the balance are “balanced” or the spring scale is set to start at zero. This is equivalent to eliminating gaps or overlaps when measuring other attributes.
For a balance scale, place the object on one pan and add units of mass to the other pan until the two pans balance
Count how many units it takes to match the object.
Pan Balance
Weights
Objects to measure
Different sized paper clips
For Distance Educators: https://www.roomrecess.com/Tools/PanBalance/play.html
To begin the lesson, explain to the students that there are tools scientists use in order to measure the weight of objects. Ask them to recall how they know how much they weigh and if there are ever times they witness their family members weighing objects. (Most students are able to identify a time their parents weighed produce or other objects at the grocery store.)
Show and model a pan balance to the students. Discuss how to make each side "balance", or become equal in weight. Tell the students that we are going to use this balance to find the weight of 3 objects: a metal disc, a wood square, and a plastic chip. (feel free to change these items based on your available materials)
Also, tell them that there are paperclips on their tray, which will be the units of weight. So, we will be trying to find how many paperclips each object weighs.What you don't tell them is that each tray has different sized clips than the other trays. This will set us up for a conversation on the importance of standard units and standard practices in science.
As teams measure the weight of objects, circulate and check for precision and ask probing questions regarding what they think about the outcomes they are getting during the task. Provide students with a sheet to record their measurements. https://docs.google.com/document/d/1u4Cpa17A1d_3UG-ZsNT_TgAa5RbJ0TsJKfOeguKpXmc/edit?usp=sharing
Measuring weight is a very precise procedure and students often want to rush through it.
In the following video, the educator spoke with a group, and several others, she had to remind them that they needed to let the balance naturally stop moving before they could decide on whether or not to put in paper clips, take some out, or if it was balanced.
Link to video:
This next group was weighing the same object, the metal disc, and found a different result. The educator explained to them that another group got a different number of paperclips and they immediately began to question why. The educator was pleased to hear them talk about variables, rather than just thinking the other team did it wrong, or that they, themselves, made a mistake.
To consolidate the lesson, call all of the student teams and have them report out their measurements of the three objects. List these numbers on the board. Obviously, they will not be the same. Some of them will be close, but others will be very far apart, due to the different sized clips. At this point, the students are still not aware they were using different sized clips. Before asking the question, ask the students if they notice anything about the reported weights of each object. Hopefully, the students will report that the numbers are different, some are close together, some are far apart, and some are exactly the same.
The question will be, "What could cause these numbers to be so different?" instruct the teams to turn into small discussion groups and talk about this. Following a few minutes, ask the class to share their thoughts as a whole and discuss standard units.
Although students will not weigh items using standard units until Grade 4, they can independently explore this concept to provide them with the background knowledge they will need for grade 4.
Introduce the students to gram weights. These weights are in 1, 5, 10, and 20 intervals. They will record their thinking on the same chart from the non-standard chart. https://docs.google.com/document/d/1u4Cpa17A1d_3UG-ZsNT_TgAa5RbJ0TsJKfOeguKpXmc/edit?usp=sharing
Explain that the students should try to figure out how to use these to re-weigh the same objects. When all groups are done, come together and compare the results.
While introducing grams, you may want to explain a bit about how the metric system works and why scientists use the metric system, all over the world. While students explore and investigate the object's weights, listen in and use the SEL (social emotional learning) assessment rubric to place students along the following continuum:
https://docs.google.com/document/d/1efJbm7njb1vXIl03AdW2GjQAPdoWg9Jtwihjusbje8s/edit?usp=sharing