Units & Systems

Initiate a class discussion prior to beginning the Science Scene.

Ask:

Have you ever hear the word "unit" used in this class? in other classes? outside of school?

How many different kinds of units can you think of? What units do these tools use to measure quantity?

Possible answers:

In this class, "unit" has been used to describe a thing we used to count or measure the quantity of something. It's also used to talk about a collection of lessons in any of our classes. Outside of school, it can mean a group of people (like a police dog K-9 unit) or a block of apartments.

Clockwise from top left, the tools in the picture measure milliliters (graduated cup); baking volumes of teaspoons, tablespoons, and cups; degrees of an angle (protractor); linear lengths like inches or millimeters/centimeters (rulers and tape measure); hours (pocket watch) and milliseconds (mobile phone stopwatch app); grams and ounces (digital scale); pounds and kilograms (luggage scale); pH value (test strips).

Some teachers have several groups of students read at the same time. Other teachers select a few students to "perform" in front of the class.

Paraphrase:

The story begins with a frustrated student who has been told by his science teacher that he must include the units in his lab reports. However, he’s not sure what the word means and complains to his friends about the multiple definitions for the word in the dictionary.

Throughout the scene, the characters reveal their misunderstandings of the terminology and seek clarification from their more informed peers.

You may want to read the entire passage out loud to the class once before assigning roles to students or dividing up into groups.

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The Script:

Setting: Emon, Markus, Yesinia, and Kaitlyn meet Haitham at his locker. He’s been upset since second period.

Emon: Why are you so frustrated with Ms. Phan in science class, Haitham?

Haitham: She keeps telling me, “Don’t forget your units!” “It’s wrong without units!” I lost points on my last lab report. She thinks I know what she means, but I don’t. I looked “unit” up in my dictionary and there are 17 different definitions! For one stupid word!

Markus: You carry that dictionary in your backpack? How heavy is that thing?

Haitham: Not the point.

Kaitlyn: Seventeen entries? That’s interesting. It’s a pretty simple word, I would say.

Haitham: (glaring) I would respectfully disagree.

Yesinia: Haitham, is one of the definitions “book chapter”? My science text has a unit on evolution, a units on microorganisms, a unit on—

Markus: (interrupting) Hey, and my cousin at UMass gets three or four units for each of her college courses.

Emon: And Ms. Schultz says our marching band performs like a single unit. I think she means the band is a group that marches in step like one person.

Haitham: Whoa! I know you’re trying to help, but all I need to know is what my science teacher means by unit.

Kaitlyn: Well, I think we’re on the right track—a unit probably means one of something, because "uni" means one. A unicycle is like a bicycle, but it just has one wheel.

Haitham: What? So Ms. Phan wants me to write one of something all over my papers? One of WHAT?

Kaitlyn: No, no. Think about it. A unit is more like a thing you use when you measure.

Haitham: Are you talking about measuring things in pounds or inches?

Kaitlyn: You got it now. A unit can be a weight or a distance or time. We measure lots of quantities. And to make sense to everyone, every measurement needs a unit. It doesn’t make sense to say the length of the field is 200. You have to say 200 feet, meters, or whatever unit you are using.

Haitham: Oh, that’s all? Okay, now I get it. I’ve been writing ratios on my paper like 60 per 1. The numbers needed units: 60 miles per 1 hour.

Markus: Right, if you don’t write the units, nobody knows what you’re talking about. (thinking) Say I told you that I drank two sodas at lunch.

Yesinia: Your teeth are gonna rot.

Markus: Not the point. What I’m saying is that you don’t know if I drank two liters, two 12-ounce cans, or two tiny cups! It really doesn’t mean anything unless you know the units.

Emon: The volume of a two-liter bottle is way more than two soda cans.

Markus: You’re right about that, Emon, but wrong about something else. What I think you mean is capacity. The capacity of a two-liter bottle is more than two soda cans because the bottle can hold more.

Emon: Whatever.

Haitham: That reminds me that Coach Frassetto said the other day that the length of the football field was 100 yards. And then he said the distance to the goalpost was 25 yards. I was wondering, why did he say length and then say distance when both are yards?

Kaitlyn: Good catch. The length often means the longest side of an object. The football field has a long side, the length, and a width, the short side. A distance is the measurement between two things or points.

Emon: We totally use length and distance for each other all the time. Probably doesn’t matter that much.

Markus: There are lots of ways these words get used, like the length of time to finish your report or going the distance for the team.

Kaitlyn: All right, here is a challenge. Another pair of units that are really similar is weight and mass. Most people think they are the same. Any of you guys know the difference?

Yesinia: Okay, I think I know this. Every night after eating a bowl of ice cream my dad weighs himself. He’s measuring how heavy he is, like last night he was 210 pounds. But our science book never says weight, it says mass. Mass is the quantity of material, or matter, like my dad and his bowl of spumoni.

Kaitlyn: That’s right. Weight also has to do with quantity of matter, but weight changes according to the strength of gravity. Mass doesn’t.

Markus: Nice. The gravity on the moon is about one- sixth of the earth. So if your father moves to the moon, he’d weigh 35 pounds.

Emon: That’s pretty funny. But this time, you’re the one who is only half right. Technically speaking, pound is a unit used for mass, not weight.

Haitham: For real? When I say that I weigh 103 pounds, I should really be saying my mass is 103 pounds?

Emon: That’s right. But it does sound kind of nerdy.

Markus: Then what is the right unit for weight?

Emon: Newton.

Markus: You’re totally making that up.

Emon: No, Isaac Newton “discovered” gravity, and since weight units have to do with gravity, they are named after him.

Kaitlyn: People can just name units after themselves?

Emon: Well, it helps if you are a king or something. Last year in Ancient Civilization class, I read that the Egyptian pyramids were measured by a royal cubit that was equal to the forearm of an Egyptian pharaoh. So the pharaoh could just establish the standard measurement.

Yesinia: Hey, if a king can name a length unit after his arm, so can we. I hereby declare one “schnoz” to equal the length of Markus’ nose.

When finished with the Science Scene, ask students to answer these three comprehension questions.

Sample Responses:

1. Ms. Phan wants Haitham to write the units for the numbers on his paper because his reports are not correct without the proper units.
2. We read a science fiction unit in English class. The unit next to our apartment is for rent. My brother was short a unit to graduate this year. The emergency doctor on TV is always calling for several units of something or other.
3. (D) A unit that many people agree should be used to compare or measure things.

What happened in the scene?

1. Can you complete this sentence to summarize why units are important?

• Ms. Phan wants Haitham to write the units for the numbers on his paper because...

2. List several situations in which the word unit is used in different ways.

3. Emon said that a pharaoh established a standard measurement called a royal cubit. What does Emon mean by the word standard?

1. A unit equal to the length of a pharaoh’s forearm
2. A flag that is often carried by soldiers into a battle
3. A unit used to measure something or someone that is standing up
4. A unit that many people agree should be used to compare or measure things

Have students discuss the question with a partner and try to reach an agreement. This is an opportunity for students to practice using scientific language as they discuss the questions.

Sample Responses:

1. Yesinia’s father would weigh 420 pounds due to the force of gravity. His mass would still be 210 pounds since mass isn’t affected by gravity.
2. Mr. Aristotle is not using the word volume correctly. The correct word is capacity. (Even so, students will not want to correct Mr. Aristotle!)
3. a) The length of our swimming pool is 25 yards. I swam a total distance of 2,000 yards yesterday.
4. b) The distance of our swimming pool is 25 yards. I swam a total length of 2,000 yards yesterday.

While the second sample sentence may make sense, and someone might understand what we mean, it doesn’t sound as accurate or precise as the first sentence.

Discuss

1. Yesinia’s father weighs 210 pounds. Markus said that because the moon’s gravity is one-sixth as strong as on earth, his weight on the moon would be one-sixth as much as on earth. But his mass would stay the same. The gravity on Saturn is about double the gravity of the Earth. What would Yesinia’s father weigh on Saturn? What would his mass equal?
2. Mr. Aristotle, a substitute teacher, told Emon’s class to “use the beakers with a volume of 500 milliliters.” Did Mr. Aristotle use the word "volume" correctly? Why or why not?
3. Make up two different sentences: one with the word "length" and the other with the word "distance." Then swap the two words and see if the sentences still make sense.