Calculating Resultant Force
- A resultant force is a single force that describes all of the forces operating on a body
- When many forces are applied to an object they can be combined (added) to produce one final force which describes the combined action of all of the forces
- This single resultant force determines:
- The direction in which the object will move as a result of all of the forces
- The magnitude of the final force experienced by the object
- The resultant force is sometimes called the net force
- Resultant forces can be calculated by adding or subtracting all of the forces acting on the object
- Forces working in opposite directions are subtracted from each other
- Forces working in the same direction are added together
- If the forces acting in opposite directions are equal in size, then there will be no resultant force – the forces are said to be balanced
Diagram showing the resultant forces on three different objects
- Imagine the forces on the boxes as two people pushing on either side
- In the first scenario, the two people are evenly matched - the box doesn't move
- In the second scenario, the two people are pushing on the same side of the box, it moves to the right with their combined strength
- In the third scenario, the two people are pushing against each other and are not evenly matched, so there is a resultant force to the left
Worked example
Calculate the magnitude and direction of the resultant force in the diagram below.
Step 1: Add up all of the forces directed to the right
4 N + 8 N = 12 N
Step 2: Subtract the forces on the right from the forces on the left
14 N – 12 N = 2 N
Step 3: Evaluate the direction of the resultant force
- The force to the left is greater than the force to the right therefore the resultant force is directed to the left
Step 4: State the magnitude and direction of the resultant force
- The resultant force is 2 N to the left