What Makes the Speedometer in a Car Fluctuate Sharply?
Mechanical A mechanical speedometer has a long flexible cable that connects it to the driveshaft of the car, which makes the wheels turn. As the end of the cable connected to the driveshaft rotates with the wheels, so does the end connected to the speedometer. As that side rotates, it turns a magnet in the back of the speedometer casing at the same speed the driveshaft is moving. The magnet rotates inside a hollow metal cup (called the speed cup) in the back of the speedmeter. The magnet doesn’t actually touch the cup as there is a buffer of air between them, but the cup is attached to the pointer in the speedometer dial. As the speed cup starts to spin around, it rotates the magnet at the same speed. The magnet creates an electromagnetic field inside the speed cup and produces an electric current. Since the current is running in a conductor and through a magnetic field, it creates motion. The speed cup is prevented from moving too much because of a hairspring that holds it in place. T
