1. Lesson Objective
Understanding force notation and finding resultants
Forces are vector quantities.
They have a size (magnitude) and a direction
There are several ways of representing a force A B

2. A B
The two forces ‘A’ and ‘B’ act on the particle shown.
What is the resultant force? (What is its magnitude and direction?)
Why is it important that we think of the object as a particle?

3. A B
The two forces ‘A’ and ‘B’ act on the particle shown.
What is the resultant force? (What is its magnitude and direction?)

4. A B
The two forces ‘A’ and ‘B’ act on the particle shown.
What is the resultant force? (What is its magnitude and direction?)

5. A B
The two forces ‘A’ and ‘B’ act on the particle shown.
What is the resultant force?

6. A B
The two forces ‘A’ and ‘B’ act on the particle shown.
What is the resultant force? (What is its magnitude and direction?)

7. A B C
The forces ‘A’ , ‘B’ and ‘C’ act on the particle shown.
What is the resultant force? (What is its magnitude and direction?)

8. Note:
If the resultant force on an object is zero we say that it is in equilibrium
If you draw forces using arrows then when an object is in equilibrium the arrows will form a closed polygon. A B C B A C

9. A B
The forces ‘A’ , ‘B’ and ‘C’ act on the particle shown.
What is the resultant force? (What is its magnitude and direction?)

10. EXAMPLE QUESTIONS
A particle has a resultant force of (8i – 7j)N under the forces
(6i + 4j)N, (–2i – 5j)N and (ai + bj)N.
Find the values of a and b. 2)

11. 1) a = 4, b = -6

12. 1) 2)

14. 3) 4)

16. 5) 6)

18. Find the magnitude and direction of the resultant force:

19. Find the magnitude and direction of the resultant force:

20. Find the magnitude and direction of the resultant force:

21. Find the magnitude and direction of the resultant force:

22. Find the magnitude and direction of the resultant force:

23. Find the magnitude and direction of the resultant force:

24. Find the magnitude and direction of the resultant of these four forces acting on a particle.