Science Class 9
How Forces Affect Motion
See how a push changes motion — three rules, with real numbers.
14 lessons · ~102 min total
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Lessons in this topic
- 0 Start here A roadmap: net force, inertia, F = ma, friction, action and reaction, and softer stops. · 4 min You are here
- 1 No force, no change A moving object keeps its velocity unless a net force acts, and friction is such a force. · 7 min
- 2 Inertia and mass Inertia is the tendency to resist a change in motion, and a larger mass has more of it. · 7 min
- 3 Force and acceleration Acceleration is net force divided by mass, and it points the way the net force points. · 9 min
- 4 Friction with numbers Friction is a force. The net force is the push minus the friction. · 8 min
- 5 Action and reaction If one object pushes another, the second pushes back equally, the other way. · 7 min
- 6 Equal forces, unequal motion The forces of a pair are equal and never cancel, but the lighter object usually accelerates more. · 8 min
- 7 Softening a stop A longer stopping time means a smaller acceleration, so the average force needed is smaller. · 8 min
- 8 Which law answers One situation, three questions: will it change, by how much, and what is the partner force. · 8 min
- 9 Force from a velocity graph The slope of a velocity–time graph gives acceleration. Mass times that gives net force. · 9 min
- 10 Two boxes, one system Boxes joined by a light string move as one system. On a smooth floor, divide the outside pull by the total mass. · 9 min
- 11 Checkpoint: force from a graph and joined boxes A graded check on the last two lessons. · 6 min
- 12 The big picture Ten ideas about how forces change motion on one screen, with the hand-off to your book. · 4 min
- 13 Track quiz Ten rules, then ten questions, one on each idea. · 8 min
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