Resolving Forces (HT Only) (AQA GCSE Combined Science: Synergy: Physical Sciences): Revision Note
Exam code: 8465
Written by: Katie M
Updated on
Resolving Forces
Higher Tier Only
Combining more than one force vector can result in
Balanced forces - where there is no resultant force
Unbalanced forces - where there is a resultant force
If a force acts at an angle, the force may be broken down or resolved
A single force can be resolved into two parts (components)
A horizontal component
A vertical component
When several forces act on an object in different directions, the resultant force can be found by adding the arrows together
The two component arrows are placed head to tail with the single force starting at the tail of the first vector and ending at the head of the second
If the force arrows form a closed loop, then the forces are balanced, in other words, there is no resultant force
Examiner Tips and Tricks
The resultant force is sometimes also known as the net force or the unbalanced force, so if you see any of these phrases used in an exam - don't panic, they all mean the same thing!
Using Scale Drawings
Higher Tier Only
Resolving vectors into components allows for more accurate calculations of resultant forces
By resolving all of the involved forces into their horizontal and vertical components and then adding or subtracting as required, a final resultant force vector can be constructed using a scale diagram
There are two methods that can be used to combine vectors using a scale diagram:
The triangle method
The parallelogram method
To combine vectors using the triangle method:
Link the vectors head-to-tail
Draw the resultant vector from the tail of the first to the head of the last
To combine vectors using the parallelogram method:
Link the vectors tail-to-tail
Complete the resulting parallelogram
The resultant vector is the diagonal of the parallelogram - measure its length with a ruler and apply the scale to find the magnitude
Worked Example
The diagram below shows two rhinos pushing against a vehicle. The two forces are at right angles to each other.
Draw a scale vector diagram to determine the magnitude of the resultant force. Label the two forces applied and the resultant, and clearly state the scale used.
Answer:
Step 1: Decide on a suitable scale
A scale of 1 cm to 1.0 kN is the most suitable for this scenario
Step 2: Use grid paper to draw the vectors head to tail and to scale
Step 3: Draw the resultant vector and measure its length
Step 4: Use the scale to convert the length to kN
The resultant force is 8.6 cm, meaning the resultant force is equal to 8.6 kN
Examiner Tips and Tricks
Students can often find scale diagrams intimidating to begin with. Start with a question that has an easy scale, for example, 1 square or 1 cm is equal to 1 unit, like the question in the worked example above. This will allow you to become familiar with the process, and as your confidence grows you can try more challenging questions. You do have to be very precise with scale diagrams, so always use a ruler and a sharp pencil, and remember to take a rubber into the exam, just in case.
Scan the exam paper as soon as you are allowed to open it, to see if you have a scale diagram question (or a graph plotting question). You will need to allocate some time to completing these more involved question types without rushing, so it is better to know in advance, rather than being surprised when you turn the page!
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