Make a simple seismograph
Suitable For
Grade 8
Difficulty
2
Time Required
<24 Hours
Supervision
Advised
What’s it about?
You may have heard of the ‘Richter scale’ used to measure the severity of an earthquake. This system was developed in 1935 by Charles Richter to measure the ‘magnitude’ or the ‘amount of energy’ released by an earthquake. It measures an earthquake’s magnitude or ‘intensity’ on a scale of 1 to 9, which means that each whole number on the scale represents a 10-fold increase in power.
Scientists use special machines called ‘seismographs’ to record the ‘seismic waves’, or movements in the earth’s crust. Each magnitude number on the ‘Richter scale’ represents the maximum amplitude of a seismic wave at a distance of about 160 kilometres. You can make a simple seismograph to demonstrate how such a machine works in the following science experiment:
Topics covered
Richter scale, Seismograph
What will I need?
- 1L SODA BOTTLE
- DOWEL STICK
- WIRE / STRING
- BOOKS
- TABLE
- FELT TIP MARKER
- A4 PIECE OF CARD
Procedure (Method)
You may have heard of the ‘Richter scale’ used to measure the severity of an earthquake. This system was developed in 1935 by Charles Richter to measure the ‘magnitude’ or the ‘amount of energy’ released by an earthquake. It measures an earthquake’s magnitude or ‘intensity’ on a scale of 1 to 9, which means that each whole number on the scale represents a 10-fold increase in power. Scientists use special machines called ‘seismographs’ to record the ‘seismic waves’, or movements in the earth’s crust. Each magnitude number on the ‘Richter scale’ represents the maximum amplitude of a seismic wave at a distance of about 160 kilometres. You can make a simple seismograph to demonstrate how such a machine works in the following science experiment:
- On a table, stack two sets of heavy books about 300mm apart and about 600mm high.
- Place a sturdy dowel stick across the stacks of heavy books.
- Fill a 2-liter soda bottle about 4/5ths with water and use wire to suspend it from the dowel stick, about 30mm above the surface of a table. The bottle should hang freely between the books.
- Make a paper ‘tube’ slightly larger than the diameter of a felt tip marker, and fix it to the side of the soda bottle. Place the pen with its tip facing down in the tube, so that it is able to slide freely up and down within the ‘tube’ with its tip touching the table.
- Tape an A4 sized piece of card to the table beneath the bottle, so that the tip of the pen is more or less in the centre of the card.
- Shake the table back and forth, gently at first and then a little harder. Make sure that you do not move the table’s legs – the shaking is enough.
- When the ‘earthquake’ is over, examine the paper. Notice the diameter of the spots on the paper!
How does it work?
A seismograph is the device that scientists use to measure the severity of earthquakes, and it can accurately record the motion of the ground during a quake. Large trucks or trains can also cause buildings to shake and can cause false readings on a seismograph if it is not isolated in some way. Therefore, accurate seismographs are connected to a large weight of some sort, to prevent the data from being influenced by surface vibrations.
In this science experiment you created a very simple seismograph by hanging a large weight (the bottle) from a rope over a table. By attaching the felt tipped pen to the weight and taping a piece of paper to the table so that the pen can draw on the paper, you can record tremors in the Earth’s crust. It would however take a pretty large tremor for you to see anything, and hence you have to shake the table to demonstrate how the seismograph works. In a real seismograph, levers or electronics are used to magnify the signal so that very small tremors can be detected. On the Richter scale, anything below 2.0 is undetectable to a normal person and is called a micro quake.
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