Resultant force
The single force that has the same effect as all the forces on an object added together, taking direction into account.
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Analogy
A tug of war: the winning side's extra pull is what decides the result.
Example
Left team pulls 500 N.Right team pulls 450 N.Resultant = 500 - 450= 50 N to the left
In practice
If the resultant is zero, the forces are balanced and the object keeps doing what it was doing.
Practice
Flashcards
- What is true about the forces at terminal velocity?They are balanced: drag equals weight, so the resultant is zero.
Interview questions
- A car of mass 800 kg has an engine force of 2,400 N and 400 N of drag. Find its acceleration.
- Resultant force = 2,400 - 400 = 2,000 N
- Use F = ma, so a = F / m
- a = 2,000 / 800 = 2.5 m/s squared
Questions people ask
How do you work out a resultant force?
Add forces that point the same way, and subtract forces that point opposite ways. Then state the direction of the bigger one. A 500 N pull to the left and a 450 N pull to the right leave a resultant of 50 N to the left.
What does a zero resultant force mean?
The forces are balanced. The object either stays still or keeps moving at the same speed in a straight line. A car on a flat road at a steady 20 m/s has its driving force exactly balanced by drag and friction, so it does not speed up or slow down.