The Benefits of Inclined Planes: Heave Ho!

Engineers continually look for and design new tools to make life easier. Students are introduced to this idea by exploring tools that they know and see everyday, in particular the inclined plane. Students act as engineers when they think of and then design tools or machines using incline planes with the purpose to simplify some task in their lives.

After this activity, students should be able to:

• Explain that an inclined plane reduces the effective "weight" of an object.
• Explain how to read a spring scale.

Figure 1. The main components of a spring scale.CopyrightCopyright 2007 Engineering K-PhD Program, Duke University

Now that we have learned about inclined planes, who can remind us of some real-world examples? (Listen to student ideas.) Examples include roads over hills, skateboard ramps, handicap access ramps, etc. And why do people need and use tools like an inclined plane? That's right - to make work easier. Well today we are going to find out how inclined planes make work easier by acting as scientists and conducting an experiment!

What we're going to do is play the role of an engineer who needs to find the lightest way to lift a bag of rocks. Using an important tool that we will discuss in a minute, we are going to find out how much this bag of rocks weighs and come up with one method to make it "weigh" less. Sound impossible? Let's find out!

Before we begin, let's become familiar with a very important tool that we will be using to do our experiments. This is called a spring scale (show an example). Does anyone know how this works? This tool is used to measure how much something weighs. See this hook ? (The hook is located on the bottom of the device; see Figure 1.) We attach this hook to whatever we want to weigh, like our bag of rocks here. See what happens when something hangs off of the scale? This plunger moves up and down, depending on how much weight is being applied. But how do we know how much the object weighs? If you look closely, you can see lines with numbers next to them on the clear part of the scale. See them? When the plunger inside this clear part is pulled down by the bag of rocks, it moves to one of these lines. See? The number next to that line is the weight of that bag of rocks. Now let's see how we can make it weigh less!

Before the Activity

• Gather materials and make copies of the three attached worksheets. The basic activity procedure is outlined through these worksheets.
• Set up at each group's work station an inclined plane, bag of rocks and spring scale. The inclined plane can consist of any hard, flat plane (wooden board, textbook, flat cardboard, etc.) that is propped up on one end between 30 and 45 degrees. While the actual inclination of the flat plane is not important, the steeper the slope, the less pronounced the effect will be.

Pre-Activity with Students

1. Use the pre-activity worksheet as a warm-up to get students thinking along the right lines. Explain the basic shape of the inclined plane, consisting typically of a flat board raised on one end. Doing this provides students with a simple template from which they can think of their own examples and applications of inclined planes. If students have trouble, provide a few of your own examples.
2. For the next activity on the worksheet, students explore some practical uses of inclined planes by filling in the provided drawing. Note that they can only use straight lines to make a path from a car to the house, meaning that they will have to use more than one line (inclined plane).

Experiment

1. Once the pre-activity worksheet activities are completed, divide the class into groups of four students each. Direct students' attention to the experiment worksheet.
2. Ask students the provided question and guide their answers correctly.
3. Have groups assemble at their work stations (wherever the inclined planes are set up) to begin their experiments. First, attach the bag of rocks to the spring scale and hold it at arm length in the air. Record the number that the scale reads in the second box on the worksheet table, next to their names.
4. Once all students in the group have completed this step, have them drag the bag of rocks (attached to the spring scale; see Figure 2) up the inclined plane and record the number on the spring scale in the third box in the worksheet table. Note: Make sure students drag their bags up the plane at as much of a CONSTANT rate as they can. This ensures that they record more accurate numbers, but depending on the age of the students, may not be as important.Figure 2. The experimental setup.CopyrightCopyright 2007 Engineering K-PhD Program, Duke University

Post-Experiment Design Activity

1. Once all students have completed these steps, gather into one large group to review the conclusion questions on the experiment worksheet. Ask students to calculate the difference in the weight with the inclined plane and the weight without the inclined plane. Make sure students get the idea that using the inclined plane made the bag of rocks feel "lighter" and easier to lift than without it.
2. When it is clear that this concept has been conveyed, direct students to the design worksheet for a fun design activity that can be altered to suit the age of the students.
3. In the provided space on the worksheet, have students identify a task or activity in their lives (getting to school, doing homework, playing a sport, etc.) that they would like to make easier in some way. Then, tell them to imagine that they are engineers who need to design a machine or tool using an inclined plane to help them with that activity. This is a purely creative and abstract exercise, so their drawings need not to be realistic, but they must incorporate an inclined plane.
4. Once their drawings are finished, have them write a sentence or two describing their machines and what they do.
5. Conclude by having students share with the class their invention ideas.

Post-Introduction Warm-Up Questions: As a class, go through the warm-up questions on the attached activity worksheet. Guide students' answers and understanding to establish the correct mindframe before beginning the experiment.

Activity Worksheets: Use the experiment worksheet and the concluding design worksheet as tools to evaluate student understanding of the concepts presented.

For more advanced students, discuss the advantages and disadvantages of using inclined planes to elevate objects. Also, basic statistical calculations can be made with the data, such as average weights with and without the inclined planes, median and mode. For further investigation, explore the effect of changing the angle of inclination on the two weights of the bag of rocks.