## Scientific Measurement Exercise

Author: Matt Wedel

Overview: In this lesson students measure irregularly shaped bones, once using a variety of measurement methods and tools, and then again using standard conventions and metric tape measures. The students learn firsthand that standardizing data collection makes observations more precise and repeatable. In addition, they learn that the forms of bones are related to their functions.

Lesson Concepts:

• Standardized measurements help us make repeatable observations and communicate our results.

• The metric system is the standard system of measurement in science.

• The same physical principles underlie the function of organisms and human machines.

California Science Education Standards:

• 5c. Students know how bones and muscles work together to provide a structural framework for movement.

• 6i. Students know how levers confer mechanical advantage and how the application of this principle applies to the musculoskeletal system.

• 7a. Students will select and use appropriate tools and technology to perform tests, collect data, and display data.

Materials:

• The cervical (neck) vertebrae of a mammal. As written, the exercise calls for a giraffe neck, but the neck of a deer or cow would work just as well.

• Puppy pads (or equivalent) on which to set the bones.

• Various tools for measuring length, including rulers, tape measures, and (if available) a yard or meter stick. At least one tool with English units only will be handy for Part 1. Part 4 calls for as many identical metric tape measures as there are groups (paper measuring tapes with metric units are available for free at the entrances of Ikea stores).

• One copy of the worksheet for each student.

Time: 50 minutes

Grouping: Groups of 2-4 students. Each neck has seven vertebrae, and each group should get their own vertebra to work on. More than one set of vertebrae can be used.

Teacher background:

Some of the methods scientists use in collecting data may seem arbitrary, overly complicated, or pointlessly persnickety to nonscientists. Scientists have developed standardized methods for collecting data to avoid confusion and misunderstanding. In this activity, students measure irregularly-shaped objects (specifically, vertebrae).

Teaching tips:

Jump right into the exercise with a minimum of explanation. There will be plenty of time for questions in Part 2. In Part 1, encourage students to measure the bones whatever way they think is best, and not just how their neighbors do it. Much of Part 2 is optional and can be shortened or dropped if time is short.

Vocabuary: vertebra, cervical, ligament

Procedure:

Part 1- Getting Started

1. Go over rules for handling bones:

• Always set them on a soft surface.

• Always pick them up with two hands (skip if using small bones).

• Hold them over the table instead of over the floor.

• Never roll them over. If you need to turn them over, pick them up and set them down again.

• If students break any of the bones, they should tell you and you can fix them. Bones break all the time, and if you know that they’re broken, you can glue them back together. If you don’t know they’re broken and they don’t get fixed, they can crumble to pieces.

2. Tell the students that they are about to get worksheets, but they shouldn’t turn them over until you tell them to.

3. Each group needs one vertebra, a puppy pad to set it on, and worksheets for everyone in the group. Have one student from each group come up to get the vertebra, and another to get the pad and worksheets.

4. Ask everyone to measure the maximum length of their group’s vertebra and write the length on their worksheet. Tell them to remember how they measured their bone.

Part 2— Introduction to Vertebrae

1. Have the students guess about the identity of the bones (both what part of the skeleton and what kind of animal). They are cervical, or neck, vertebrae from a giraffe.

2. Ask the students, what do vertebrae do? They support the body and protect the spinal cord—point out the large hole in each vertebra, through which the spinal cord passes.

3. Ask the students how many vertebrae you passed out (seven). See if anyone knows how many vertebrae they have in their necks (also seven). Except for manatees and sloths, all mammals have seven cervical vertebrae. We inherited this trait from our common ancestor.

4. Show the students cervical #7 from the base of the neck. Ask them how it is different from all the others (tall spine).

5. Turn over worksheets.

6. Draw a suspension bridge on the board (see example below) and ask the students if they recognize it. Briefly explain the function of a suspension bridge: the towers bear the weight; the main cables connect the towers to each other and to the ground on either side; the roadway is suspended from secondary cables. Now erase two thirds of the drawing and replace the center span with the body of a cow, and draw a cow’s head on one end of the bridge. Mammals have a large ligament (a piece of tough tissue that connects bones) that holds up the head and neck. (If anyone asks, this is called the nuchal ligament; nuchal is Latin for ‘back of the neck’.)
 How to turn a suspension bridge into a cow:

7. Have the students feel the backs of their necks. At the base of their neck, they will feel a large bump. This is the spine of cervical #7. They can’t feel the spines of the other vertebrae as easily because they lie underneath the big ligament.

Part 3— Talking about the Measurements

1. uppose we want to know how long this giraffe’s neck was (for an ecology study, or to compare to bones of an extinct species). Can we just add up the various measurements? Call on specific students to report the lengths of the vertebrae they measured. Make sure to get at least one English measurement and at least one metric measurement. Ask students if they see any problems with the measurements. Elicit the response that they need to use the same units.

2. Quick review of metric vs. English measurements. Ask the students if they know why scientists use the metric system.

• Metric system is universal, and not specific to a single culture.

• Based on powers of 10, so conversions are easy.

• SO we need to measure the vertebrae again using the metric system.

3. How did different people measure their bones?

• Draw a vertebra on the board (see example below). Ask different students how they measured their vertebrae, and draw lines representing their measurements on the diagram.  How to draw a vertebra. The Xs and dotted line show how everyone should measure the vertebrae in Part 4.

• Ask the students whether these different ways of measuring the vertebrae will give consistent answers.

• SO we need to measure the vertebrae again, and everyone needs to do it the same way.

Part 4— Measuring Again

1. This time, have the students work in groups (or, time permitting, in pairs).

2. Measure each vertebra on the right side, from the back of the ball to the front of the socket, using a metric tape measure. The first vertebra in the neck (c1, or the atlas) differs from the others in having no ball and two sockets. Have the students measure from the margins of the sockets on the right side.

3. Once the group or pair has measured a particular vertebra, pass it on to the next group. Each group or pair should measure all seven vertebrae and add up the measurements to find the length of the neck.

4. Write the neck lengths obtained by several groups on the board and compare them. How do the different neck measurements compare to the different lengths of individual vertebrae from Part 1?

5. If there is time, line up some puppy pads and lay out the whole neck. Have the students measure the articulated neck and compare to the results of their calculations.