in today's video we're going to look at three body diagrams and how we can use them to find the resultant force on an object when we say free body diagrams all we mean are simple diagrams that show all the forces that are acting on a particular object we do this using force arrows so if we took the example of a plane flying through the sky we will draw its free body diagram by adding a bunch of different arrows that represent all the forces acting on the plane so it would have one going forwards which would be its thrust one backwards for air resistance or drag one downwards for its weight and one upwards for its lift because all forces are vectors each of these has to have both a magnitude and a direction we can see the direction from which way the arrows are pointing but the magnitude of the force comes from how long each of the arrows are and to be more precise we can label each of them in newtons now because all these forces are acting in different directions some of them are going to cancel each other out and once you've taken that into account what we'd have left is the resultant force which you can describe as the overall force on an object it's normally easiest to do this by looking at the horizontal and vertical directions separately and calculating the overall size and direction of the resultant force in each case for example the vertical component of this free body diagram involves a force of 80 000 newtons up and 80 000 newtons down so when we subtract one from the other we're left with zero nutrients overall for the vertical component for the horizontal component though we have 120 000 newtons to the right and only 90 000 newtons to the left so by doing right minus left we get a resultant force of 30 000 newtons in the right direction so overall taking into account the vertical and horizontal components would still have an overall resultant force of 30 000 newtons to the right if though we had a slightly different scenario where the air resistance was 120 000 newtons instead then we'd be doing 120 000 minus 120 000 and so the horizontal resultant force would be zero now both the horizontal and vertical components will be perfectly balanced and so we would say that the object is in equilibrium because there's no resultant force acting on it anyway that's everything for this video so hope you found it useful and we'll see you soon