Forces, resultant force and friction
Learn what forces can do, how to combine forces along a line, and how friction and drag affect movement. This is Cambridge International IGCSE Physics 0625, separate from Egypt’s Egyptian Baccalaureate / Thanaweya Amma and not a Year 3 course.
A force is a push or a pull
You cannot see a force itself, but you can notice what it does. A force can change an object’s size or shape, such as squeezing a sponge. It can also change the object’s velocity: its speed, its direction, or both.
Open the worked example
A moving football is kicked. The kick is a force. It can make the ball move faster, slower, or in a new direction. A force can also bend or squash an object.
Quick check: Name one change a force can make to an object.
Think, then reveal: It can change the object’s size or shape, or change its velocity (speed or direction).
See how opposing forces combine
Interactive model · balance a moving trolley
Change the forward push and the opposing resistance. In this simple model the push acts right and resistance acts left; choose whether the object is moving right or starting at rest.
Resultant = driving force − resistance = 50 N − 30 N = 20 N to the right
When the resultant is zero, an object already moving keeps a constant velocity; an object at rest stays at rest. This model does not calculate acceleration.
Practise, then read the explanation
Try each question first. Open the optional hint if needed, then submit to see why the answer works.
Optional hint
Think about squeezing a sponge and kicking a ball.
This original lesson aligns to Cambridge IGCSE Physics 0625 syllabus objectives 1.5.1.1 and 1.5.1.3–1.5.1.8 as grouped in the supplied Volume A. It covers the effects of a force, resultant force along a straight line, balanced and unbalanced forces, changes to velocity, solid friction and heating, and drag in liquids and gases. Source reading: Physics-0625 Volume A, PDF pp. 58–63 (printed pp. 50–55). The interactive model is a simple one-dimensional representation and does not calculate acceleration.