A seismograph is an instrument that can record seismic actvity. Seismic activity is when the ground moves or shakes. This movement creates waves, similar to sound waves, that travel through the ground.

Seismographs are used to locate and measure earthquakes. They can also show you what's in the ground. Scientists use seismic waves kind of like sonar. By slamming a weight or putting dynamite into the ground, seismic waves will flow through the rock. If the waves hit something, an echo will bounce back. A seismograph hooked to a computer will measure those waves. The computer measures the timing of the waves to determine how deep in the earth the object is and what substance the waves are hitting, like rocks, bone, or oil.

Paleontologists use them to locate skeletons;

Newton's Law of Inertia states that any object at rest will continue to stay at rest until acted upon by an outside force. A recording device hooked to the weight makes a line on a piece of paper. If the frame moves up, a downward line will appear on the paper. If the frame moves down, it will make a upwards mark on the piece of paper. Seismographs measure how much the earth moves by using the metric system or by using the Richter Scale.