This activity uses simple materials to allow students to explore how earthquakes affect structures, causing some buildings to vibrate while others appear to stand still. The consistent rhythm in which the "buildings" (i.e. the plasticine balls) swing at is known as their natural frequency.

When you look at a building, it appears to be a rigid structure. All buildings, however, have some flexibility. This is particularly noticeable at the top of a tall building on a windy day. The shorter the building the stiffer it is, and the higher its natural frequency.

This activity has been adapted from the San Diego Supercomputer Center's TeacherTECH Science Series

### Objectives

• Model and describe the effect of earthquakes on buildings.

### Materials

• Per Group:
plasticine
florist wire: 3 pieces of the same thickness & 1 thicker wire
a piece of styrofoam or floral dry oasis block

### Key Questions

• Part 1:
• Did the balls swing with the same rhythm?
• Which one has the highest natural frequency (sways back and forth the fastest)?
• Have you ever felt a short building sway in the wind? A tall building?
• Part 2:
• Which wire swung harder?
• Which had the highest natural frequency? The lowest? (The wider "building" will generally have the higher natural frequency due to its stiffness.)
• How does this relate to building structure?
• Part 3:
• Which ball-and-wire combination has the lowest natural frequency (sways back and forth the slowest)? (The heavier "buildings" will have the lowest natural frequency.)
• Part 4:
• What did you observe with the big ball? The small ball?
• Which one moved the most? Why?

### What To Do

1. Roll three pieces of plasticine into balls about 2 cm in diameter.
2. Stick a piece of wire (all the same thickness) into the middle of each of the plasticine balls.
3. Push the wire (the end away from the plasticine ball) into the block so that the balls are all at different heights; 10, 15 and 20 cm work well. The plasticine represents the weight of the building and the wire represents the flexibility of the building.
4. Pull the ball on the tallest wire back about 3 cm, then let go.
5. Repeat this for the other plasticine balls.

1. Roll two pieces of plasticine into balls about 2 cm in diameter.
2. Stick a piece of wire into each plasticine ball, as in Part 1, but this time use different thicknesses of wire.
3. Push the wire (the end away from the plasticine ball) into the block so that the balls stand at the same height. The plasticine represents the weight of the building and the wire represents the flexibility of the building.
4. Pull both balls back about 3 cm, then let go.

1. Roll three pieces of plasticine into three different-sized balls. Diameters of 1 cm, 2 cm and 3 cm work well.
2. Stick a piece of wire (all the same thickness) into each ball and push the wires into the block so that the balls are at a height of about 15 cm.
3. Pull all three balls once and compare what happens.
• (Note: If you don’t see a difference, re-roll the balls so that you have a greater variation of size, then re-test.)

1. Roll one small and one bigger plasticine ball.
2. Stick them onto two pieces of wire (same thickness) and push them into the block at the same height. About 20 cm would work well.
3. Pull the bigger ball back about 3 cm, then let go.
4. As the students watch the ball swing, ask them to make a note of the rate and speed at which the ball moves back and forth. This is its natural frequency.
5. Now, make an earthquake! Push the block back and forth in time with the ball’s movement. In other words, you’re wiggling the block at the natural frequency of the ball.
6. Notice how two motions amplify when they are moving in the same direction at the same time. This is known as resonance.
7. Repeat with the smaller ball. What is different?

### Extensions

• What other things can affect the natural frequency of buildings?
• How would that affect the vulnerability of buildings during an earthquake?
• Which would be more likely to fall: a building with a higher or lower natural frequency?

### Other Resources

IRIS Earthquake Science | How will 3 buildings, engineered equally, on different bedrock, react to an earthquake?

Government of British Columbia | Master of Disaster Youth Education

Government of British Columbia | Earthquake Preparedness and Response

U.S. Geological Survey | Earthquake Hazards Program | Earthquakes for Kids

Cybersleuth Kids | Earthquake Resources

Survivors

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

Egg BB

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

Comet Crisp

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

T-Rex and Baby

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Buddy the T-Rex

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Geodessy

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Science Buddies

Artist: Ty Dale

From Canada, Ty was born in Vancouver, British Columbia in 1993. From his chaotic workspace he draws in several different illustrative styles with thick outlines, bold colours and quirky-child like drawings. Ty distils the world around him into its basic geometry, prompting us to look at the mundane in a different way.

Western Dinosaur

Artist: Ty Dale

From Canada, Ty was born in Vancouver, British Columbia in 1993. From his chaotic workspace he draws in several different illustrative styles with thick outlines, bold colours and quirky-child like drawings. Ty distils the world around him into its basic geometry, prompting us to look at the mundane in a different way.