【Science】Grade 3: Objects and Weight
Hello everyone! Let’s explore the science of "Objects and Weight" together.
"Does the weight change if the shape changes?" "Do objects have the same weight if they are the same size?"
The things we touch every day are full of interesting secrets. It might seem tricky at first, but you'll be just fine if you visualize the results of your experiments! Let’s have fun learning.
1. Units of Weight and How to Express Them
The terms we use to describe how heavy an object is when measured are called units.
In science, we mainly use these two units:
● Gram ( \( g \) )
Used for measuring small or light objects.
Example: A 1-yen coin (about 1 \( g \) ), an eraser, a pencil, etc.
● Kilogram ( \( kg \) )
Used for measuring heavier objects. When you have \( 1000g \), it becomes \( 1kg \).
Example: A 1-liter milk carton (about 1 \( kg \) ), your body weight, etc.
【Key Point】
\( 1kg = 1000g \)
This relationship is very important! It will come up in math too, so make sure to memorize it well.
2. What happens to the weight when the shape changes?
If you roll up some clay or stretch it into a long thin shape, does the weight change?
The answer is... "Even if the shape changes, the weight stays the same."
Why?
Because even if the shape changes, the "amount of material" that makes up the object has not increased or decreased.
For instance, if you take a piece of aluminum foil and "crumple it up loosely" versus "crush it tightly," they look completely different, but their weight is the same.
【Common Mistake】
You might think, "It must be heavier because it's crushed tightly into a smaller space!" But remember, if the amount of material remains the same, the weight stays the same. Don't be fooled!
3. What happens to the weight when you break an object into pieces?
What happens if you take one object and break it into smaller pieces?
The answer is... "Even if you break it into pieces, the total weight remains the same."
Example: The weight of 10 chocolates measured while inside a box is the same as the weight of those 10 chocolates measured separately on a plate.
【Summary】
Whether you change an object's shape or break it into pieces, its weight does not change.
4. What happens if the type of material is different?
Even if objects look like they are the same size (volume), what happens if they are made of different materials?
The answer is... "If the types are different, the weights are different!"
For example, let's compare a "wooden ball" and an "iron ball" of the same size.
・Iron ball: Heavy and solid
・Wooden ball: Much lighter than iron
・Plastic ball: Sometimes even lighter than wood
As you can see, remember that "even if the size is the same, the weight is determined by the material the object is made of."
【Trivia】
If you compare the same size of "cotton" and "iron," the iron is obviously much heavier. This is because the amount of "particles" that provide the weight packed into the same space is different.
5. Tools for measuring weight: "Scales"
In science, we use "scales" (platform scales) or "pan balances" to measure weight accurately.
Tips for using a scale:
① Place it on a flat surface
If it's on a slant, you won't get an accurate measurement.
② Adjust the reading to "0" (zero)
Make sure the needle points exactly to "0" when nothing is on the scale.
③ Read the scale from straight ahead
If you look from an angle, you might misread the number. The trick is to look at the needle directly from the front!
【Step Up!】
Scale markings have small lines (minimum increments).
Checking "how many grams one mark represents" at the very beginning is the shortest path to becoming a scale master!
★ Conclusion: Chapter Summary
1. Use units like \( g \) (grams) and \( kg \) (kilograms) for weight.
2. Changing the shape or dividing an object into pieces does not change its weight.
3. Even if the size is the same, weight differs depending on the type of material.
4. Place scales on a flat surface and read them from straight in front.
Some of this might have seemed obvious, while other parts might have been a surprise! Try picking up various things around you and guessing, "Which one is heavier?" It will make science even more fun!
I’m rooting for you!