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Unit E2

Scene: Machines Everywhere

Duration: Approximately 50 minutes

In this Science Scene, a dialogue to read aloud as a class, students encounter important concepts as they read a discussion among fictional students about what force and work are. The characters sketch how pulleys are essential to how some elevators works. Then, as the same characters volunteer to set up a school book fair, the Science Scene more formally presents the terms work and force, and explains how they are measured with newtons and joules.

LEARNING OBJECTIVES

Students begin to make sense of the terms machine, force, and work by comparing their common and scientific meanings. Students refine their thinking about machines in a scientific context.

Students demonstrate careful reading by identifying accurate details.

Students consider the perspectives of the characters through related questions.

Teacher Tips

- Think ahead about how you will assign the three roles (Cooper, Olivia, and Hamza) to read the script aloud as a class (or, less ideally, in small groups). Note that students often willingly take on roles regardless of the gender of the characters.
- While it is possible for the students to read the PDF of the script online, we suggest printing the script for the students so they can hold it in their hands and mark it as they read.
- Prior to the reading the script, explain to students that they will encounter new vocabulary terms and ideas that may not be familiar. Reassure them that this lack of familiarity is okay. The reading is meant to introduce the ideas, not explain them completely.
- Review the focus words of the week. The focus word chart linked on the unit overview page should be used as a resource for students to review definitions and sample sentences.

Teacher Tune-ups

Teaching Notes

ACTIVITY OVERVIEW

- Set the context (10 minutes)
- Engage with the script (20 minutes)
- Explore "work" as a scientific term (20 minutes)

Set the context (10 minutes)

Engage with the script (20 minutes)

Assign three students to read the parts of Hamza, Olivia, and Cooper. This dialog is an introduction to the concept of machines and work.

As the fictional students point out in the dialogue, the terms machine, force, and work have both common and scientific meanings. Early in the dialogue, Cooper gives an informal definition of work. It may help to have your student read this definition twice.

Many of your students will follow Cooper’s example and turn their pencil into a windshield wiper. Take a moment to do this as a class. Tell them that the pencil is acting as a lever.

As the scene unfolds, Cooper draws a sketch of how one type of elevator works and the group discusses the concepts.

Consider taking a few minutes to discuss the drawing.

:

- What is holding the elevator up?
- Olivia mentions that there is a pulley. Can someone point out the pulley?
- One end of the cable is attached to the elevator. What is the other end attached to?
- Cooper says that the elevator is a complex machine. What does he mean by complex machine?

Setting: Cooper, Olivia, and Hamza are hanging out in the library working on their homework.

Hamza: I never have the energy to do my homework.

Olivia: I keep telling you, Hammy, that’s an attitude problem, not an energy problem.

Hamza: I wish I had a machine to do all that work for me.

Cooper: If you had done your homework, you’d know what work machines really do. Hint: not homework.

Hamza: If you say so, Nerd Cooper. What is this “work” that machines do?

Olivia: I thought work was what energy did.

Hamza: (sarcastically) Is your name Nerd Cooper?

Cooper: Be nice. And she’s right. Work is when you change how something is moving: speed it up, slow it down, change its direction or how it's spinning—like when you kick a soccer ball.

Olivia: See Hamza, work can be fun!

Cooper: Basically it can be any movement that lines up with a push or pull. I mean that’s the science term “work.” But in everyday English we use the word “work” for a lot of different things.

Hamza: So, scientifically speaking, if I kick a ball and the ball knocks over a chair, I did the work of making the ball go, and then the ball did the work of knocking over the chair?

Cooper: Hmmm...

Olivia: I think so, Ham. You had energy from eating food, and then you exerted a force when you kicked the ball. Your kick gave energy to the ball, and the ball used the energy to knock over the chair.

Cooper: It’s cool to think about how something simple like kicking a ball has all these things going on.

Hamza: (daydreaming) I’m a machine on the soccer field.

Olivia: Well, they actually don’t allow machines on a soccer field, but they do in a hockey rink.

Hamza: You mean the Zamboni machine that smoothes the ice?

Cooper: Actually, she’s talking about the hockey stick.

Olivia: And you would know that if...

Hamza: I know! I know! If I did my homework. Wait, how is a stick a machine? It doesn’t take gas or electricity. That can’t be right.

Cooper: It is a machine! The way to figure it out is to think about whether it can transmit work.

Olivia: Coop, did you get the thing on the homework about pretending your pencil was a windshield wiper?

Hamza: What!? Oh great. Now I’m curious. I can’t believe I’m curious about homework. What have you two done to me?

Cooper: Here. Try it. Hold your pencil in front of you by the end and shift it back and forth like a windshield wiper. A small motion of your fingers causes a large motion at the other end of the pencil. That means it’s a machine. A lever to be exact.

Hamza: Oh, that’s kind of cool. I see the connection to the hockey stick. A player moves the stick at one end, but the stick moves a lot more at the other end and applies force to the puck so it goes faster than the hand moves. Wham!

Olivia: I guess golf and baseball are similar. They use levers. But I know people think of machines as things like cars or elevators. Not sticks.

Cooper: Well, it’s not that cars and elevators aren’t machines. They’re more like a bunch of machines put together into a complex machine. Look:

Cooper sketches a car and an elevator.

Hamza: I get the wheels on a car, but you mean when I’m in an elevator it’s held up with a string?

Olivia: A strong string. More like a metal cable. And the pulley is like a version of the wheel.

Hamza: Stop! I don’t think I want to know all this stuff. What if the cable breaks?

Cooper: It won’t break if you respect the load limit. It’s posted inside the elevator.

Olivia: Even if you overload an elevator, I bet it would be okay. Engineers and scientists study specifications carefully for safety.

Hamza: They better, or else I’m taking the stairs!

Explore "work" as a scientific term (20 minutes)

In this part of the activity, an example of lifting books from the floor onto shelves demonstrates how force and work can be measured.

First, students read an informal definition of a newton. In the formal definition, gravity makes 1 kilogram of mass exert about 9.8 newtons of force. Students are asked to consider that if one apple weighs 1 newton then a book weighs 10 newtons.

Students typically confuse the terms force and work. When a student pushes against a door, force is involved. Consider asking students, “What is a force that is pulling you down all the time? This force is pulling everything down, and we never think about it.” The answer is gravity.

In physics, work is defined as force times a distance traveled. Returning to the example of a student pushing against a door, if the door doesn’t open, there is no work being done, only a force against the door. But if the door opens, there is work. Work must include some movement. Work is measured in joules. One joule equals 1 newton times 1 meter of travel.

The “Turn and Talk” asks students to determine from the sketches and description who is doing the most work and who is doing the least. You may need to clarify that each book weighs the same. Hamza is applying force (lifting) one book at a time and raising each book 1 meter in one second, so he is doing the least amount of work. Cooper is lifting 1 book at a time, but 2 meters high. He is clearly working twice as much as Hamza. Olivia’s work is equal to the work done by Cooper because she is lifting 2 books at a time but only 1 meter high.

Consider having student groups with different answers briefly debate who is correct. Then, if students do not readily understand, tell them that they will now use multiplication to calculate the work done by each student.

The last third of the activity introduces joules, the standard unit of measurement for work. Students may not immediately realize that work is the product of the force of an object times the distance the object moved. To arrive at the joules of an object, the force must be in newtons, and the distance in meters. So 1 joule is 1 newton * 1 meter.

Students read that Hamza expended 10 joules each time he lifted a book. Moving a force of 10 newtons, 1 meter high can be written as 10 N * 1 m = 10 joules.

Olivia lifted 2 books, with a combined force of 20 newtons, 1 meter high, so he worked 20 joules each time he lifted a book.

Cooper's work equaled 10 newtons (for 1 book) * 2 meters = 20 joules.

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