Physics trivia

# Electronic spines

Electronic speed bumps work from sensors, properly spaced and placed on the road, which determine the speed of cars.

Traffic violations committed by speeding are perhaps the most common and most frequent. In order to limit the speed of cars on roads, generating more safety for both drivers and pedestrians, electronic speed controllers, or the popularly known electronic speed bumps, are installed on busy roads, which usually have a large flow of pedestrians, hospitals, , schools etc.

The operation of these equipment is based on the physical principle of calculating the average speed . Under the track, and properly spaced, are installed two sensors that are activated from the passage of the vehicle, these sensors are connected to a central that, in turn, determines the speed value. When the vehicle activates the first sensor, the time count starts, which is interrupted as the vehicle passes through the second sensor. From the ratio between the measured time and the space between the sensors, the vehicle speed is determined. If this speed exceeds a set maximum value, the system takes an image of the car and generates a ticket.

Attempting a sudden deceleration when you are close to the electronic speed bump can cause collisions between vehicles, as the vehicle behind may not have enough space for braking. The right thing is to always obey the speed limits.

Example: Assume that the distance between sensors installed on a street is 1.5m and that the time for a vehicle to pass determined by the system was 0.075s. What will the speed of this vehicle be determined by the electronic speed bump?

From the definition of velocity we have: V = Δs
Δt

V =  1.5m   = 20 m/s → V = 20 m/sx 3.6 = 72 Km/h
0.075s

The vehicle speed indicated by the electronic spine would be 72 km/h.