Force, mass and acceleration; circular motion
Build confidence with the Supplement / Extended equation F = ma, then learn how an inward force keeps an object moving in a circle. This is Cambridge International IGCSE Physics 0625, separate from Egypt’s Egyptian Baccalaureate / Thanaweya Amma and not a Year 3 course.
A resultant force changes velocity
A resultant force is the overall force after all the pushes and pulls have been combined. When it is not zero, the object accelerates: its velocity changes. A velocity change can mean speeding up, slowing down or turning.
Open the worked example
A moving trolley has a forward resultant force. Its acceleration points forward, so while it is moving forward its speed increases.
Quick check: What does an acceleration tell you has changed?
Think, then reveal: The velocity has changed. That can be a change of speed, direction, or both.
Explore force and circular motion
Interactive model · change resultant force or mass
This model treats the force shown as the resultant after all forces have been combined. It uses F = ma; it is not a separate calculation of friction or circular motion.
a = F ÷ m = 12 N ÷ 4.0 kg = 3.00 m/s² forwards
Try doubling the mass while keeping the force fixed. The acceleration halves. Try doubling the force while keeping the mass fixed. The acceleration doubles.
Interactive diagram · follow the moving object
Choose a position around the circle. The blue arrow is the instantaneous velocity (tangent); the red arrow is the inward force, at 90° to it.
If this inward force vanishes, the object continues in a straight line tangent to the circle at its current position.
Practise, then read the explanation
Every idea in this lesson is labelled Supplement / Extended. Try each question first, open a hint if needed, then submit to see why the answer works.
Optional hint
Recall the equation and the direction rule together.
Original learning material aligns to Cambridge IGCSE Physics 0625 syllabus objectives 1.5.1.11 and 1.5.1.12, both Supplement / Extended, as grouped in the supplied Volume A. It teaches resultant force, F = ma and acceleration direction, then qualitatively describes the inward perpendicular force in circular motion and how speed, radius and mass affect the force needed. Circular-motion relationships are not used for numerical calculations. Source: Physics-0625 Volume A, PDF pp. 71–76 (printed pp. 63–68).