Two or three years ago, there was an exchange of several articles in "Primary Science Review" about the question: "What is the best way of naming the forces acting on a descending parachute?" (Harrison, 2001; Harlen, 2002; Sell, 2002). Stuart Harrison reported that, according to the Qualifications and Curriculum Authority (QCA), a third of 11-year-old children referred to "upthrust" in a SAT (Standard Assessment Test) question, when the QCA preferred "air resistance" because upthrust "is miniscule in comparison to the force of air resistance for a falling parachute". Sell considered it harsh that the QCA regarded use of the term upthrust as uncreditworthy in its mark scheme. More recently, Lee and Tan (2004) have suggested that particle models of matter should be employed in primary teaching. This article therefore attempts to show how particles can be used to help teachers and children grasp the difference. (Contains 5 figures.)