Q: Why does the pin have a vertical force in this diagram (Static equilibrium)? The diagram depicts as follows: A mass (M) sits a a distance (d) away from the end of a board of length L. The board has a mass of m and is held to a wall by a pin and string. The string has a tension (T) and is at angle θ to the board. The pin is frictionless. The entire set-up is in static equilibrium. Side note: In the diagram I called the board the scaffolding. What I don't understand is why the pin has forces (Fy & Fx). I sort of understand why the pin must have a horizontal force (Fx) b/c otherwise there would be no other force to oppose the horizontal competent of tension. What I don't understand is why Fy must exist. To be honest, I don't even understand what Fy really is. Shouldn't the vertical component of the tension be enough to oppose the weight of the block and board? If so, there's no need for another upward vertical force. I'd be really grateful if anyone could help me on this!