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Make Your Own Seismograph!

In this activity, students learn how a seismograph measures the shaking of the earth during an earthquake. 

A typical seismograph has a pen attached to a heavy weight. The weight is free to swing back and forth, or to bounce up and down on a spring. The pen touches a rotating cylinder of paper, so that the pen draws a line as the cylinder rotates.

If the ground does not move, the pen draws a smooth straight line. But when the ground moves, the cylinder moves along with it. The heavy weight, on the other hand, has a lot of inertia and stays still. The result is that the pen draws a zigzag line on the shaking cylinder.

The stronger the shaking, the sharper the zigzags. This zigzag picture made on the paper roll is called a seismogram.

Objectives

  • Model and describe the effect of earthquakes on buildings.

Materials

  • Cereal box, shoe box, or milk carton
    Cardboard sheet (as a base)
    Plastic or paper cup with lid
    Pencil
    Scissors
    Long strip of paper about 5 cm wide
    String
    Sand

Key Questions

  • Why doesn't the pencil move when the box does?

What To Do

  1. Stand the box on its end. Cut rectangular windows on the front and back sides of the box leaving only 2 cm of box on the edges for support. Punch a hole in the centre of the top of the box.
  2. In the middle of the bottom edge of the box, cut 2 narrow horizontal slots about 5 cm wide. Slide the long strip of paper through these slots.
  3. Pierce a hole at the centre of the bottom of the cup, and another in the centre of the lid.
  4. Punch 2 holes on opposite sides of the cup, near the rim. Thread string through these holes.
  5. Push a pencil, point down, through the holes in the bottom of the cup.
  6. Fill the cup with sand around the pencil and put on the lid, with the top of the pencil sticking out. You may want to fill the space between the pencil at the bottom of the cup with plasticine to prevent sand from spilling out.
  7. Hang the cup inside the box by threading the strings you tied onto the cup through the hole in the top of the box.
  8. Adjust the length of the string so the tip of the pencil touches the strip of paper threaded through the bottom cuts of the box.
  9. Glue the bottom of the cereal box to a larger piece of cardboard.
  10. Shake the cardboard base back and forth. The weighted pencil should stay put and will make a mark on the paper strip. Ask a friend to pull the strip of paper slowly through the slits.

Extensions

  • Can you record a seismogram without directly moving the box? How does this affect 'real' seismometers? How can this effect be reduced?

Other Resources

Science World Resources | Full Unit |  Earthquakes
Video | How a seismograph works