One person pushes a crate forwards with a force of 40 N while another person pulls it backwards with a force of 15 N. Taking forwards as positive, what is the resultant force?

1. Force is a vector, so both its size and its direction matter. 2. The two forces act along one straight line, so a simple sign method can be used. 3. Forwards has been chosen as positive, so the backwards force is negative. 4. The two vectors are then plus 40 N and minus 15 N. 5. Adding them gives plus 25 N. 6. A positive answer points in the direction chosen as positive, so the resultant is 25 N forwards. 7. Getting 55 N means the two forces were added as if they pointed the same way. 8. Getting 25 N backwards keeps the size right but reads the sign the wrong way round. _Source: Siyavula Physical Sciences Grade 10 (Everything Science, CC BY 4.0), Chapter 20: Vectors and scalars_