How Speedometers Work?

The job of the speedometer is to indicate the speed of your car in miles per hour, kilometers per hour or both. 

1. When the engine turns over, the driveshaft turns to make the wheels spin round.
2. The speedometer cable, powered by the driveshaft, turns as well.
3. The cable spins a magnet around at the same speed inside the speed cup. The magnet rotates continually in the same direction (in this case, counter-clockwise).
4. The spinning magnet creates eddy currents in the speed cup.
5. The eddy currents make the speed cup rotate counter-clockwise as well in an attempt to catch up with the magnet. Remember that the magnet and the speed cup are not joined together in any way—there's air in between them.
6. The hair spring tightens, restraining the speed cup so it can turn only a little way.
7. As the speed cup turns, it turns the pointer up the dial, indicating the car's speed.

How does a seismograph work? What is the Richter scale?

A seismograph is the device that scientists use to measure earthquakes. The goal of a seismograph is to accurately record the motion of the ground during a quake.

The main problem that must be solved in creating a seismograph is that when the ground shakes, so does the instrument. Therefore, most seismographs involve a large mass of some sort. You could make a very simple seismograph by hanging a large weight from a rope over a table. By attaching a pen to the weight and taping a piece of paper to the table so that the pen can draw on the paper, you could record tremors in the Earth's crust (earthquakes). If you used a roll of paper and a motor that slowly pulled the paper across the table, you would be able to record tremors over time. However, it would take a pretty large tremor for you to see anything.

In a real seismograph, levers or electronics are used tomagnify the signal so that very small tremors are detectable. A big mechanical seismograph may have a weight attached that weighs 1,000 pounds (450 kg) or more, and it drives a set of levers that significantly magnify the pen's motion.

What is the Richter scale?

The Richter scale is a standard scale used to compare earthquakes. It is a logarithmic scale, meaning that the numbers on the scale measure factors of 10. So, for example, an earthquake that measures 4.0 on the Richter scale is 10 times larger than one that measures 3.0. On the Richter scale, anything below 2.0 is undetectable to a normal person and is called a microquake. Microquakes occur constantly. Moderate earthquakes measure less than 6.0 or so on the Richter scale. Earthquakes measuring more than 6.0 can cause significant damage.

How does a sphygmomanometer (blood pressure gauge) work?

A blood pressure gauge is simply a way to measure the performance of the pump and the pipes.

There are two numbers in a blood pressure reading: systolic and diastolic. For example, a typical reading might be 120/80. When the doctor puts the cuff around your arm and pumps it up, what he/she is doing is cutting off the blood flow with the pressure exerted by the cuff. As the pressure in the cuff is released, blood starts flowing again and the doctor can hear the flow in the stethoscope. The number at which blood starts flowing (120) is the measure of the maximum output pressure of the heart (systolic reading). The doctor continues releasing the pressure on the cuff and listens until there is no sound. That number (80) indicates the pressure in the system when the heart is relaxed (diastolic reading).

If the numbers are too high, it means that the heart is having to work too hard because of restrictions in the pipes and this raises your blood pressure.

High blood pressure can cause the heart to fail (from working too hard), or it can cause kidney failure (from too much pressure).