Forcediagrams are used to help understand a given scenario and show which forces are acting on which particles and in which direction they are acting
In diagrams an arrow is used to represent a force acting on a particle which shows the direction in which the force is acting
The magnitudeof the force is normally written next to its arrow
What types of forces could be involved?
Specific types of force encountered (which may not be mentioned in the question nor labelled on a given diagram) are: weight (W N), tension (T N), thrust (T N), friction (F N) and normalreaction (RN)
Remember that the diagram is drawn to help understand the scenario - cars, blocks, etc are modelled as particles occupying a singlepoint in space and so all forces acting on the car, block, etc act at that same singlepoint
The main forces that you will see are:
tension (a “pulling” force) acts away from a particle, thrust (a “pushing” force) acts towards it
weight is W = mg where m kgis the mass of the particle and g is the acceleration due to gravity – usually g = 9.8 m s-2
If you are told, or are using g = 9.8 m s-2 ensure you round your finalanswer to twosignificantfigures (as 9.8 is rounded to 2 s. f.)
If you are told to use g = 10 m s-2ensure you round your finalanswer to onesignificantfigure (as 10 is rounded to 1 s. f.)
friction acts parallel to the surface in the opposite direction to motion
the normalreaction acts perpendicular to the surface (and friction)
Always draw a force diagram if appropriate.
If a diagram is already given then add to it as you progress through the question.
If a diagram is too small or it gets too complicated then draw a new diagram.
You may be able to manage with just drawing the section of the diagram you are dealing with in any particular question part.
Unless told otherwise, use g = 9.8 m s-2 and round your final answer to two significant figures.
Some questions may direct you to use g = 10 m s-2 in which case round your final answer to one significant figure.
Dan graduated from the University of Oxford with a First class degree in mathematics. As well as teaching maths for over 8 years, Dan has marked a range of exams for Edexcel, tutored students and taught A Level Accounting. Dan has a keen interest in statistics and probability and their real-life applications.