This app deals with forces exerted on a body (assumed as point-sized). You can vary the number of single forces by using the choice box at the ride side. It is possible to change the sizes and directions of these forces (blue arrows) by dragging the arrowheads to the intended positions with pressed mouse button.
If you want to know the total force which is exerted on the body, you have to carry out a vector addition. As soon as you have clicked on the button "Find out resultant" the program will show you the necessary parallel translations of the force arrows and then draw the arrow of the resultant (red). The construction can be cleared by a mouse click on the lower button.