The BOSS Model:                        Name: _______________ E.N.___

Building Oscillation Seismic Simulation                 Period: _________ Due Date: ____

 

RATIONALE

During an earthquake, buildings oscillate. If the frequency of this oscillation is close to the natural frequency of the building, resonance may cause severe damage. The BOSS model allows students to observe the phenomenon of resonance.

 

FOCUS QUESTIONS

Why do buildings of different heights respond differently in an earthquake?

 

OBJECTIV ES

Students will:

1. Predict how a structure will react to vibrations (oscillations) of different frequencies.

2. Perform an experiment to establish the relationship between the height of a structure and its natural frequency.

3. Describe the phenomenon of resonance.

 

Demo: Oscillation

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Discussion Notes:

 

 

 

 

 

 

 

 

 

 

 

Procedure:

a. Hold the base stationary, pull the wooden number 1 out several centimeters to the side, and release it. As the rod oscillates, use a stopwatch to measure the time for 10 oscillations.

Record this number

b. Practice until you can get almost the same swing each time, then repeat the measurement  four times. Calculate the average of these four times. Now calculate the natural frequency of the number by dividing 10 cycles by the average time.

Record it. Repeat this procedure for the other three numbers.

c. Measure the height of each assembly from the base to the top, and record it.

d. Plot height versus natural frequency on the graph provided.

 

Post Lab Questions:

1. From what you have learned, do the earthquakes with the highest numbers on the Richter Scale always do the most damage?

 

2. Discuss your results. Be sure to point out the connection between the experimental results and the way real buildings resonate. Other things being equal, do taller buildings have lower natural frequencies than short buildings?

 

3.  Explain how seismic waves caused by earthquakes produce oscillations, or vibrations, in materials with many different frequencies.

Include: Natural frequency, Resonance, ground shaking,

 

4. Hypothesize what would happen when buildings of two different heights, standing next to each other, resonate from an earthquake.

 

5. “How could you add structural elements to reduce resonance in a building?”

 

ADAPTATIONS AND EXTENSIONS

One way to protect a building from resonating with an earthquake is to isolate its foundation, or base, from the ground with devices much like wheels. This technique is called base isolation. Structural engineers are now developing the technology to place buildings on devices that absorb energy, so that ground shaking is not directly transferred to the building. Add standard small wheels from a hardware store to your models as an illustration of one of the many base isolation technologies, or add wheels to your own BOSS model, then shake the table. Better yet, place the model in a low box or tray and shake it. Then take out the model, fill the box with marbles or BBs, and replace the model on this base. Now shake the box. Can you come up with other base isolation techniques?

 

Observations:                                                  Inference(s):

 

 

 

 

 

Record oscillation times in the data table below in the appropriate place for each rod assembly. These times are measured in seconds per 10 cycles. Repeat the measurement four times to minimize human error, then record.

Caution: Start the stopwatch as a numbered block reaches its maximum swing and start counting with zero, otherwise you will end timing only nine swings. Practice this until your times for 10 oscillations are fairly close to each other.

Calculate the average time for each oscillation by adding four measurements and dividing by four. Record.

Calculate the natural frequency. Divide 10 cycles by the average time (do not simply move the decimal point). Frequency is measured in hertz, or cycles per second. Record.

1. How much variation do you notice among the four trials?

___________________________________________________________________

2. What relationship do you notice, if any, between the height of the rods and their natural frequencies?

________________________________________________________________________________________________________________________________________

 

B. Heights of the Rod Assemblies

1. Measure the height of each rod assembly from the base to the top of the block and record it.

Rod Assembly

Height (cm)

 

#1

 

#2

 

#3

 

#4

 

 

2. What is the approximate difference in height between #1 and #2, #2 and #3, and so on?

________________________________________________________________________________________________________________________________________

 

3. Plot the height versus the natural frequency of each rod assembly on the graph provided. You should have four data points. Connect the points with the best fitting straight or curved line you can.

4. What kind of line did you get from your data?

____________________________________________________________________

5. As the height of the rod assemblies gets larger, what happens to their natural frequency?

____________________________________________________________________________________________________________________________________________________________________________________________________________

C. Summary

1. What variable is manipulated in this experiment? (How do the four rod assemblies differ from each other?)

____________________________________________________________________

 

2. What is the responding variable in this experiment? (What did you measure?)

____________________________________________________________________

3. What does oscillate, or vibrate, mean?

____________________________________________________________________

4. Define frequency.

____________________________________________________________________

____________________________________________________________________

5. Why does only one rod assembly oscillate greatly (or resonate) when you wiggle the base?

____________________________________________________________________

____________________________________________________________________

 

6. What is resonance?

____________________________________________________________________

____________________________________________________________________

7. How are the rod assemblies like buildings?

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

8. (extra credit) How can a building be protected from resonating with seismic vibrations?

____________________________________________________________________