A road has a speed limit for a reason. The reason is because when you go faster the handling of the car is more sensitive. Which means it spins out of control easier than going at a legal Speed!
Studies We need to know the speed of an object so that we can predict the time it takes to travel at a certain speed and distance. Example a GPS tells you the time it takes to arrive to your destination depending on the speed your going.
We calculate the speed of an object using light gates. Light gates are a detector that calculates the speed using a beam Led/Ir as something goes thru it the beam is "cut".
Light gates are used on roads to detect the speed of a car. If the car goes over the speed limits a picture is taken of the car's number plate and it's sent to the police which will later on send a fine to the driver!