All,
Many thanks for taking the time to offer your explanations. Putting them all together has enabled to grasp the principal that you've all been driving at.
Kind regards,
Peter
Grateful if someone could explain why, if Newton's 2nd law says F=ma, I've read warnings and cautions in several physics books that mass times acceleration is not a force. Is it because the equals sign does not mean equals as in 2+2=4, perhaps?