It is impossible to measure the speed of an object at an instant.
It is only possible to find the object’s speed over a small distance and time.
This is achieved using a light gate and a thin card of length say 10 cm.
When the card interrupts the light beam it turns off a light sensor and starts an electronic timer.
The timer stops when the card passes the light beam and the sensor picks up the light signal again.
The near instantaneous speed is calculated by: