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Learning how to use tools to find the size and weight of different materials.
Imagine you and a friend are sharing a giant chocolate bar. You say your piece is bigger, but your friend says theirs is! How can you prove who is right without eating it first?
Have you ever looked at two boxes and thought the bigger one must be heavier? Sometimes our eyes can play tricks on us! A giant box might be filled with light fluffy cotton balls, while a tiny box might be filled with heavy rocks. Measuring is the way scientists find the 'true' size or weight of something. When we measure, we use tools to get a number that everyone can agree on. This is called being accurate. In science, we don't just say something is 'big' or 'heavy'—we use numbers to describe it exactly.
Quick Check
Why is it better to measure an object than to just look at it?
Answer
Because our eyes can be tricked, and measuring gives us an accurate number that everyone agrees on.
Length is the distance from one end of an object to the other. To find length, we use a tool called a ruler. Most rulers have two sides. One side measures in inches, and the other side measures in centimeters (). Scientists usually use centimeters because they are used all over the world! The most important rule for using a ruler is the Zero Rule: always line up the very start of your object with the mark, not the very end of the plastic or wood.
Let's find the length of a pencil in centimeters: 1. Place the ruler flat on the table. 2. Line up the flat eraser end of the pencil exactly with the mark on the side. 3. Look at the pointy tip of the pencil. 4. If the tip reaches the number , the length is .
Quick Check
Where should you place the end of an object when you start measuring with a ruler?
Answer
You should always line it up with the mark.
Weight tells us how heavy an object is, or how much gravity is pulling on it. A balance scale is a tool used to compare the weight of two different things. It works like a playground seesaw! If you put a heavy object on one side and a light object on the other, the heavy side will sink down toward the table, and the light side will lift up into the air. If the two objects weigh exactly the same, the scale will stay perfectly level in the middle.
Imagine you have a large strawberry and a small lime. 1. Place the strawberry in the left bucket of the scale. 2. Place the lime in the right bucket. 3. If the right bucket (the lime) sinks down, it means the lime is heavier than the strawberry, even if they look similar in size!
Quick Check
If a balance scale is perfectly level (straight across), what does that tell you about the two objects?
Answer
It tells you that the two objects have the same weight.
When we measure, the number isn't enough—we need a unit. If you tell a friend a bug is '5 long,' they won't know if you mean 5 centimeters or 5 giant footsteps! Common units for length include centimeters () and meters (). Common units for weight include grams () and kilograms (). Using these units helps scientists share their discoveries so that anyone, anywhere, can understand exactly how big or heavy an object is.
Which tool would you use to see if a toy car is longer than a toy truck?
If you put a rock on the left side of a scale and a feather on the right, what will happen?
True or False: A big object is always heavier than a small object.
Review Tomorrow
In 24 hours, try to explain to someone why you shouldn't start measuring at the '1' mark on a ruler.
Practice Activity
Find three different items in your room (like a shoe, a book, and a spoon). Use a ruler to measure each one in centimeters and list them from shortest to longest!