Students will be able to measure objects using non-standard units. They will then explore reasons to use standard units.

Students have not had many chances in life to measure weight, nor to explore the units of measure. As scientists, it is important to express findings in a standard way. This lesson helps students determine the why of that concept.

5 minutes

Today, we will explore the idea of mass. I will ask the students, **"What do scientists do in order to measure the mass of matter?"**

I will have students turn and talk about this question in order to create a common interest in today's exploration. As the partners discuss, I will listen in and try to find a partnership that will discuss the idea of a scale, or a tool to find weight.

The idea of finding the weight of an object is part of teaching children that investigating every property is important in the description of that object. The 5 senses aren't enough often times.

10 minutes

To begin the lesson, I will explain to the students that there are tools scientists use in order to measure the weight of objects. I will ask them to recall how they know how much they weigh and if there are ever times they witness their parents weighing objects. (Most student are able to identify a time their parents weighed produce or other objects at the grocery store.)

I will show and model a pan balance to the students. I will discuss with them how to make each side "balance", or become equal in weight. I will 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.

I will 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 objects weighs.

**What I 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.

25 minutes

As teams measure the weight of objects, I will circulate and check for precision and ask probing questions regarding what they think about the outcomes they are getting during the task.

Measuring weight is a very precise procedure and students often want to rush through it. As I spoke with this group, and several others, I 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 paperclips, take some out, or if it was balanced.

This next group was weighing the same object, the metal disc, and found a different result. I explained to them that another group got a different number of paperclips and they immediately began to question why. I was so pleased to hear them talk about variables, rather than just thinking the other team did it wrong, or that they, themselves, made a mistake.

10 minutes

To close the lesson, I will leave the students with a lingering question, which we will visit in the next lesson.

I will call all of the student teams to the community area and have them report out their measurements of the three objects. I will 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 my question, I will 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.

My question will be, "What could cause these numbers to be so different?" I will then instruct the teams to turn into small discussion groups and talk about this.

Following a few minutes, I will ask the class to share their thoughts as a whole and then tell them that tomorrow I will give them another option to think about.