So we finally come to a subject none of us likes talking much about--weight! Because, you know at some point one of your little darlings is going to ask, "How much do you weigh?". Luckily, in kindergarten, we deal strictly in non-standard units of measurement. So I'm honest. I tell them.
Approximately 15,000 cubes.
If they can figure out how many pounds that is, then I really am a phenomenal problem-solving teacher!
Texas kindergartners are only required to compare 2 objects based on their weights. A truck weighs more than a book. An apple weighs less than the school. You get it. But, if they are ready, I usually expose my kids to using a balance and weighing with non-standard units.
The student directly compares the attributes of length, area, weight/mass, capacity, and/or relative temperature. The student uses comparative language to solve problems and answer questions. The student is expected to:
(D) compare two objects according to weight/mass (heavier than, lighter than or equal to).
- K.MD.1. Describe measurable attributes of objects, such as length or weight. Describe several measurable attributes of a single object.
- K.MD.2. Directly compare two objects with a measurable attribute in common, to see which object has “more of”/“less of” the attribute, and describe the difference. For example, directly compare the heights of two children and describe one child as taller/shorter.
To introduce this concept, we simply practice comparing weights by holding different objects in our hands. Of course, some objects are a little too heavy to actually pick up. Luckily, the kids already have a solid schema--most can easily tell you that a car weighs more than a soccer ball.
I have the kids use their water bottles and find objects that weigh less and weigh more. They record their answers in their math journals, and we make a class chart, as well.
The interesting part comes when they find an object that is fairly close in weight to the water bottle. Even I would have a hard time determining which one actually weighs more, so that presents an excellent opportunity to discuss--How can we know for sure which one weighs more? (We'll get to that in a few days when we start measuring with cubes.)
Another excellent discussion to have is:
How does an object's size affect its weight? Does bigger always mean heavier?
I pull out several objects specifically for this conversation--a feather, a marble, a beach ball and a baseball. First, I ask the kids Which ones are bigger? Both the feather and the beach ball are bigger. Then I ask Which ones are heavier? The marble is heavier than the feather, even though it is bigger. And the beach ball is much lighter than baseball, even though it is much bigger.
Why? Most kids will quickly realize that the beach ball is full of air, and air is very light. It's fun to hear what they think is inside of a baseball (rock). After some discussion, we decide that the more "stuff" (or matter) is inside of a given area, the more it will weigh.
Then we discuss the difference between weight and mass.
I don't actually want to get too technical and risk the formation of misconceptions. I just want them to see that size and weight are not always related and that big objects can sometimes be light and that small objects can sometimes be heavy.
As a follow-up activity/warm-up, I have the kids complete a heavy/light sort in their math journals.
WHAT is a "shoebox" balance, you ask? Only one of my favorite activities ever! Full disclosure: My team makes fun of me for this activity. I don't know why--it's an excellent way for children to figure out how a balance works. I never introduce "real" balances until we have played with our shoebox balances for a while.
You will need: a cylindrical object of some sort (a can works); a long, flat object (like a shoebox lid); and some play-doh (obviously, dollar store stuff works just fine).
Place a blob of play-doh on the table and place the can into it. This is so the can will not roll away. The can needs to be as straight as possible, so be careful to push the can down into the play-doh evenly.
Now, balance the lid on top of the can. Do not use play-doh to stick the lid on the can. That's cheating. Just balance it. It takes practice. I let the kids practice balancing the lid with nothing in it until they get the hang of it. They are learning that the lid has to be centered on the can for it to work. Why? Because then, the same amount of lid is on each side--so each side "weighs" the same.
After a while, I let the kids start placing objects on each side of the "balance." I give them an assortment of my mixed math tools--cubes, counters, etc. I do not tell them how to do it--I let them figure it out on their own! If one side falls down, they figure out that they have to add something to the other side. If that side then falls down, they might take that object out and try something lighter. It's all about trial and error. They are problem-solving!
They are gaining a solid understanding of how a balance works. (You might notice that my kids are using domino box lids and plastic cylinders from a building set I have. Whatever works!)
By the way, if you see this (look below), you might want to discuss with the students why it's not quite right. Technically, it is balanced. But because it is not on the curved part of the cylinder, it's a whole lot easier!
So as my kids are exploring, I ask them---Does this remind you of anything? Usually, someone will say a teeter-totter, or see-saw. I ask them how a see-saw works--and how that is like our shoebox balances? The light side goes up...the heavy side goes down! And what has to happen to make it balance? Both sides have to be the same weight--or equal.
Would it be fun to play on a see-saw with an elephant? No--because the elephant is so much heavier, you would be stuck in the air all the time. This is something that most kids can relate to--connecting their new learning to what they already know.
So after my kids have had lots of time to play with their shoebox balances, I bring out the "real" balances. I also collect a variety of objects for them to explore with.
The first activity is to compare objects to see which weighs more using the balance. Again--do not tell the kids how to do it. Guide them through questioning, but do not model it.
For a challenge, have the kids figure out which of the objects they compare weighs the most. That's true problem-solving! Watch to see what strategies the kids use to keep track of the objects they weigh. This is definitely a challenge. I always have them work together in a group for this problem.
Here's my old recording sheet, but I've updated it for this year and included it with the blackline masters. I chose objects that most people already have in their classrooms or that are easily accessible.
This is just more practice using a balance. I give each group and eraser and a variety of objects. They see how many different combinations of objects they can find to balance the eraser.
So here, instead of just comparing objects, we are actually weighing them using non-standard units. In the past, I have used bears, but this year, I'm using cubes. The kids will have to do some rounding, for sure. Sometimes 6 cubes isn't enough to make it balance perfectly, but 7 is too many. I tell them to get as close as possible.
While they're working, I ask them what the benefit of using the cubes (bears) to measure with would be. (It's a common unit that you can then compare weights with).
When they're done, I ask which object weighed the most? They can answer very easily...here it was the rock, because 13 cubes was the most. Was it harder or easier to tell which object was heaviest today, as compared to yesterday? They should (hopefully) say it was easier today--because they knew how many cubes each object weighed, they did not have to go back and compare each object. They had a common unit by which to compare.
Here I have the kids explain, either verbally or in writing, how a balance works.
And we make an anchor chart.
This little girl used tiles. She put out 5 tiles to represent the 5 tiles on one side of the balance. And then she added tiles until she got to 12 (because she knew she would need 12 on both sides to make it balance). She then counted how many more she added to get the answer 7.
First, I draw balance and I count to make 5 cube for 12. Now 5 cube need another 5 to make a 10. And 10 cube need 2 more so that 5+2+7 and so 5+7=12 and that make 12 and 12 and it make both equal.
She is clearly ESL, but brilliant, right? She kept adding on until she got to 12. 5+5+2...
They have to figure out that if the book weighs 5 cubes, there are 3 cubes left. So the pencil must weigh 3 cubes.
I put most of my blackline masters here in this packet. You can download them for free by clicking on the link below. You'll see I have updated most of the pages.
And now, I need to get off the computer and go get some exercise. Because to be honest, I could stand to lose about 2,000 cubes!