Balancing to compare mass
How can a child tell which of two things is heavier, and what does it mean when a balance stays level?
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Two things can be compared by how heavy they are, not only by how long or tall they are. A child can feel the difference in two hands, and a two-pan balance shows it plainly: the side that goes down holds the heavier thing, and a level beam means the two are the same. The star’s word is mass; with a young child, just say “how heavy”, “heavier” and “lighter”.
This builds on comparing two objects side by side. Each day takes about ten to fifteen minutes. Keep it to comparing: no numbers of grams or pounds yet.
Day 1: Heavier and lighter in two hands
You need: a shoe and a sock, a book and a sheet of paper, a full water bottle and an empty one, and two crayons that look alike.
Put one thing in each of the child’s open hands. Ask, “Which one pulls your hand down more? That one is heavier. The other one is lighter.” Let the child say the full sentence: “The book is heavier than the paper.” Then swap the hands and ask again, so the child sees the answer stays with the thing, not the hand.
End with two things that feel nearly the same, like the two crayons. Hands cannot tell, and that is fine: “My hands can’t tell. Tomorrow we’ll use a balance to check.”
Practice. Hand the child each pair, one thing in each hand.
- A shoe and a sock. Which is heavier? Answer: the shoe.
- A book and a sheet of paper. Which is lighter? Answer: the paper.
- A full water bottle and an empty one. They look the same size. Which is heavier? Answer: the full one. Same size does not mean same heaviness.
- Two crayons that look alike. Which is heavier? Answer: hands can’t tell; they feel the same.
Day 2: The side that goes down
You need: any two-pan balance (a classroom bucket balance, or a coat hanger with a paper cup hung from each end), plus an apple, a grape, two matching blocks, a crayon and a shoe.
Start with the balance empty and show that the beam sits level. Ask the child to press one side gently: “Down. Now let go.” Then put an apple on one side and a grape on the other. Ask, “Which side went down? The side that goes down has the heavier thing.” Put a block on each side: “Neither side went down. Level means they are the same.” Then let the child check the Day 1 crayons.
Practice. Point to each balance in the picture.
- Balance A. Which is heavier? Answer: the apple. Its side went down.
- Balance B. Which is heavier? Answer: neither. The beam is level, so the blocks are the same.
- Balance C. Which is lighter? Answer: the crayon. Its side went up.
- Balance C. Which is heavier? Answer: the shoe.
- With the real balance, put a pencil on one side and nothing on the other. What happens? Answer: the pencil side goes down. Anything is heavier than nothing.
Day 3: Big is not always heavy
You need: the balance, a big empty cereal box, a rock that fits in the child’s hand, a small full can of food and a blown-up balloon.
Hold up the big box and the small rock. Ask, “Which do you think is heavier?” Many children pick the bigger one, and that guess is welcome. Now put both on the balance. The rock side goes down. Ask, “Which is bigger? Which is heavier? Are they the same thing?” Say it together: “The box is bigger, but the rock is heavier.” Do the same with the can and the balloon.
Practice. Point to each balance in the picture.
- Balance A. Which is heavier? Answer: the rock. It is much smaller than the box, but its side went down.
- Balance A. Which is lighter? Answer: the big box.
- Balance B. Which is heavier? Answer: the can.
- Balance B. Which is lighter? Answer: the balloon. It is the bigger thing, but its side went up.
- With the real balance, the child picks two things in the room, guesses which is heavier, then checks. Answer: whatever the balance shows. The guess comes first; the balance decides.
Exercises
Show the child the check picture.
- Balance A. Which is heavier, the sponge or the toy car? Is the bigger thing the heavier one?
- Balance B. Which is heavier, the eraser or the 3 cubes?
Answers
- The toy car; its side went down. No: the sponge is bigger, but it is lighter. A child who has it reads the beam, not the sizes.
- Neither. The beam is level, so the eraser and the cubes are the same. A child who has it says “the same” instead of picking one.
Where this goes next
When two things cannot both go on the balance at once, a third thing can stand in between, which is comparing with a middle object. Counting how many cubes balance a toy turns “heavier” into a number, which leads to units and later to story problems with grams and kilograms. A level balance is also the picture behind an equation: whatever is added to one side must be added to the other to keep it level, the idea in Inverse operations and the properties of equality.