[Music] hi and welcome back to free science lessons. co.uk by the end of this video you should be able to use Vector diagrams to calculate the resultant of two forces acting at an angle and this is for higher students only in the last video we started looking at resultant forces remember that when several forces act on an object they could be replaced by a single Force which has the same effect and scientists call this single Force the resultant Force we saw several examples where we calculated the resultant Force now in all of these examples the different forces are acting parallel to each other but what if the forces are acting at an angle I'm showing you typical question here two forces are acting on an object one force has a magnitude of 10 Newtons and the other Force has a magnitude of 8 Newtons the angle between the two forces is ° calculate the resultant Force now this looks much more difficult than it actually is we start by making a scale drawing showing the forces involved scientists call this a vector diagram we're going to say that 1 cm equals 1 Newton so here's the object and remember that this is a free body diagram so we just show a point we now use a ruler to draw a 10 cm long Arrow to represent the 10 Newton Force using a protractor we measure an angle of 30° and here it is and now we use a ruler to draw an 8 cm Arrow to represent the 8 Newton Force now we need to create a parallelogram to do that we copy the 8 cm line and position it at the head of the 10 cm Force Vector we should also use a protractor to double check that the angle is still 30° now we copy the 10 cm line and position it at the head of the 8 cm Force vector and then we draw a line from the tals of the force vectors to the other side of the parallelogram finally we measure the length of the vector and work out the resultant force that this represents in this case the vector is 17.5 cm long so this means that the resultant force is 17.5 Newtons we can also use a protractor to measure the Angles and here they are now in the exam you need to draw your vector diagram as accurately as you can however the examiners will accept a small range of possible answers for the resultant Force here's one for you to try a force of 280 Newtons and a force of 320 Newtons are acting on an object there's an angle of 20° between the forces calculate the resultant Force now to do this you'll need to decide on a scale for example 1 cm for 40 Newtons you will then need to draw a vector diagram and work out the resultant Force so pause the video now and try this yourself okay using a ruler we draw the two vectors to scale and again I've used 1 cm equal 40 Newtons and using a protractor we make the angle between them 20° now we complete the parallelogram and now we draw in the vector for the resultant Force this Vector has a length of 14.8 CM remember that 1 cm equals 40 Newtons so the resultant force is 592 Newtons and once again we can use a protractor to measure the Angles and here they are we remember find plenty of questions on using Vector diagrams in my Vis Vision workbook and you can get that by clicking on the link above [Music]