Measuring
How do you measure an object with a ruler? (hint: be specific about where you place the ruler).
Align one end of the object with the zero mark (the starting point) of the ruler. Then, read the measurement at the other end of the object on the ruler's scale.
What are the units for meters?
m
You might say a desk is about 1 meter long. In that case, the desk is an example of this.
a referent
The windowsill
How many centimeters are in one meter?
100 centimeters
what are the units for centimeters?
cm
This is why we use referents—so we can do this more easily without tools.
estimate measurements
What did Ms. Phelps use to measure as a referent for 2m?
The carpet.
3 meters
If I had a surfboard that was two and a half meters long, how would I represent it in written form?
2.5 m
The width of your pinky finger is close to this length unit.
1 centimeter
If a ribbon is 250 cm long, it is this many meters and centimeters.
2 meters and 50 centimeters
If I had an object that was 1 meter long and I took away half of it, how long would it be now?
The object would be 50 centimeters long after taking away half.
This is the metric unit you would use to measure the height of a door.
m
A teacher says the school mascot statue is about 180 centimeters tall. A student says, “That’s about the size of a notebook.” Using your knowledge of referents, explain why the student’s estimate is way off, and give a more accurate comparison for 180 centimeters.
A notebook is only about 20 to 30 centimeters tall, while 180 centimeters is much taller—about the height of an adult person. So a better referent for 180 centimeters would be the height of a grown-up or a tall door handle.
This object is about 30 cm long and often found in a classroom.
a ruler
How do you measure the length of a string (provide all the steps)
You take the string and place it down on a flat surface holding each end, then you stretch it out to make sure it is straight with no bumps in it. After that, you take your ruler and place it next to the strong starting from the zero mark (the beginning of the ruler), then you look to see where the end of the string is on the ruler and record that number as the length of the string.
This unit is shorter than a meter but longer than a millimeter.
A centimeter
You are told that a garden hose is 1,200 centimeters long. A student says, “That’s about as long as my shoe.” Using your understanding of referents, explain why that statement doesn’t make sense and suggest a more realistic object or length to compare it to.
A shoe is only about 20–30 centimeters long, while 1,200 centimeters is the same as 12 meters. That’s much longer than a shoe—it’s about the length of a school bus or the width of a gym. So a better referent for 1,200 centimeters would be something very long, like a swimming lane or several large tables lined up.
A soccer field is usually around 100 meters long. This is how many centimeters it is.
10,000 centimeters