Still water: Water at rest or stationary position is known as still water. Usually at ponds or lakes when water is at rest without any movement on the surface.

Stream: The moving water in the stream is known as stream. 

Stream is of two types-

  • Up-stream : If a boat is moving in the opposite direction of water flow or stream then it is known as upstream.
  • Downstream : If a boat is moving in along the direction of water flow or stream then it is known as downstream.

Stream Formulas 

Let us consider a boat is travelling in still water with speed u km/hr and speed of the stream is v km/hr

  1. Speed downstream  = (u+v) km/hr
  2. Speed upstream = (u-v) km/hr

Let us consider the speed downstream is x km/hr and speed upstream is y km/hr

  1. Boat speed in still water = ½(Downstream speed + Upstream speed)= ½(x+y) km/hr
  2. Rate of stream= ½(Downstream speed – Upstream Speed) = ½(x-y) km/hr
  3. Average speed of boat = {(Upstream speed x Downstream speed)/boat’s speed in still water}

Let us take “T” hours for a boat to reach a point in still water and comes back to the same point then, the distance between the two points = {( u^2-v^2) x T}/2u,

Where “u” Speed of boat in still water

             “v” speed of stream

Let us take “T” hours more to go to a point in upstream than downstream for the same distance, then the distance = {(u2-v2) x t}/2v,

Where “u” is the speed of the boat in still water

             “v” is the speed of the stream

If a boat travels a distance downstream in “t1’ hours and returns the same distance upstream in “t2” hours then, 

The speed of the man in still water = [v x {(t2+t1)/(t2-t1)}] km/hr

Where “v” is the speed of the stream.                                                            

What do you need to Know about Upstream and downstream SPF’s?

Upstream and downstream SFPs function the same way as other SFPs, except that they use Wavelength-Division Multiplexing (WDM).  WDM allows for the transmitting and receiving signals to co-exist on the same fibre strand.  This allows a single fibre cable strand to simultaneously transmit and receive a signal.

You must use upstream and downstream SFPs in pairs.  You cannot use two upstream or two downstream SFPs together.  

Method to solve the problems:

  • The first and most important tip is that a candidate must memorise the important formulas to answer the questions correctly. Memorising the formulas will help candidates answer straight forward questions without making any errors
  • Do not confuse yourselves between the concept of upstream and downstream as the question may not specifically mention the two terms and instead mention “ in the direction of flow” or “against the direction of flow”
  • Reading the questions carefully will help candidates avoid making silly mistakes, so do not be in a rush while reading the instructions mentioned in the article
  • Ensure that you do not panic reading the length of the question or the terms used in the questions as boat and stream questions asked in the Government exams are mostly direct and not too complex. It is just the formation of the question that makes it sound complicated

    Conclusion:

    In this article we come to know what is upstream and downstream, How they are calculated mathematically. We learned about various terms related to streams like still water, rate of stream etc. If students have any queries regarding anything they are free to ask any question.