# Measure Twice!

1.6 based on 10 ratings

#### Updated on Mar 22, 2013

Grade Level: 6th - 7th; Type: Physical Science

### Objective

Determine whether it is possible for different measurements of the same objects can have different values

### Introduction

On a skills level, this project serves to acquaint students with the differences which may occur in making length measurements, namely the probability and possibility of making an error and how we as scientists attempt to reduce this error. Students are involved in the process of accounting for the probable error and finding a way to reduce this error. This is an essential skill in experiments where measurement is a critical skill.

This science fair experiment also serves to acquaint students with the process of putting together a science fair project, clearly delineating an objective, stating his or her own hypothesis as to the anticipated outcome and at times justifying the hypothesis based on previous research. In addition, the student learns to follow directions, record observations, employ a variety of data collection vehicles such as use of charts, graphs and photos. Finally, the student organizes a bibliography of all the various resources used in obtaining the vital data. The entire project serves as an excellent experience in training the mind to organize and process data in a systematic, organized way for a very specific purpose.

### Research Questions

• What do we mean when we speak of possible error in linear measurement?
• Why do scientists claim that the average value in linear measurement is probably the best value?
• How does one estimate possible error in the case of linear measurements?
• Is the above process applicable to other types of measurements?
• How do we define the term validity in the process of experimentation?
• How does one define the term reliability?
• Is sample size an important factor in this project?

### Terms to Know

• Measurement
• Possible error
• Validity
• Reliability

### Materials

• 5 meter sticks
• 5 index cards or student worksheets
• Student’s desk
• Calculator

These materials may be readily available from your science or math classroom.

### Experimental Procedure

1. Gather all the materials that you will need for this project.
2. Construct and state your hypothesis. Do you think that different measurements of the same object can have different values?Why?
3. Obtain permission from your teacher to have five pupils in your science class who have volunteered to assist you to obtain your basic measurement data after school or during the lunch period.
4. Reproduce the student index cards provided below and distribute to your five volunteers.
5. Reproduce the data chart provided below to record all of the measurements and all of your calculations.
6. Give your five volunteers clear cut directions, namely they are to complete the information requested on the card and record their measurements to the nearest tenth of a centimeter. They will make the following measurements: the length, height and width of the teacher`s lab table (if not available use the teacher`s desk) and the length, height and width of a student`s desk.
7. The volunteers are to return the cards to you and not exchange the data they have obtained with anyone.
8. Given all of the data, you will calculate the sum of the measurements for each of the dimensions measured separately, namely, the length of the lab table or teacher`s desk, the width of the lab table or teacher`s desk, the height of the lab table or teacher`s desk and the same for the students’ desks.
9. You will then find the average value for each group of measurements, dividing the sum of the number of measurements made by 5.
10. In each group of measurements, find the largest measurement made and calculate the difference between the largest measurement and the average.
11. Now find the smallest measurement made in each group and calculate the difference between the smallest and the average. The larger of the two differences found in steps 9 and 10 is an estimate of the possible error.
12. Record your findings. Explain why there were different values for the same measurement? Provide as many reasons that you can think of.
13. What could you have done to reduce the possible errors?
14. It is often suggested that the average value in all of these cases is the best value and should be used. What do you think?
15. Write up your report. Make certain to include your hypothesis. Include all of your data as well as a compilation of your bibliography. Be certain to include what you found in your research as to methods recommended to reduce error for as the title of this project indicated error is possible, would you not agree?

Copy of Index Card (to be reproduced)

Name:

 Objects Measured Length in cm Width in cm Height in cm Lab Table Student`s Chair

Data Chart (to be reproduced)

 Objects Sums Averages Differences L Differences S Error Lab Length Lab Width Lab Height Chair Length Chair Width Chair Height

### References

• Goodstein, Madeline Numbers in Science Menlo Park, Ca. Addison Wesley, 1987