Forces, Friction & Equilibrium
Read everyday force situations correctly: identify the forces, decide their directions, compare them, and determine whether an object stays at rest, moves at constant speed, or accelerates.
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Track what changes
Distance counts the path; displacement compares final and initial position with direction.
Velocity includes direction. Turning changes velocity even at constant speed.
Acceleration means velocity changes: speeding up, slowing down, or turning.
For the same object, greater height means greater gravitational potential energy.
Gravity changes vertical motion while ideal horizontal motion continues.
Rolling combines translation and rotation; mass distribution affects rotational inertia.
STATE → CHANGE → RESULT
STATE: identify the starting motion or energy state. CHANGE: mark exactly what changes—speed, direction, height, time, or input. RESULT: follow the physical consequence without adding an unstated assumption.
Five relationships to recognize
Turning: same speed can still mean changing velocity because direction changes.
Height: the same object has greater gravitational potential energy at the higher point.
Equal-time marks: increasing gaps mean increasing speed; equal gaps mean constant speed.
Projectile: at the highest point, vertical velocity is momentarily zero but horizontal velocity remains in the ideal model.
Rolling: equal-mass, equal-radius objects can roll differently if their mass distributions differ.
Common traps
Same speed does not mean same velocity when direction changes. Distance and displacement differ when a path reverses. A projectile is not stopped at its highest point. The heaviest rolling object does not automatically arrive first.
Can you transfer the idea across five forms?
This diagnoses your next practice step; it does not verify mastery.
Practice at the level you need
Verify the competency
Mastery requires 5/5. An unsuccessful attempt loads a different set.
Quick clarifications
Can acceleration happen without speeding up?
Yes. Changing direction changes velocity.
At the top of a projectile path, is it stopped?
No. Vertical velocity is momentarily zero, but horizontal velocity remains in the ideal model.
Does the heaviest rolling object always arrive first?
No. Ideal rolling can depend on rotational inertia and mass distribution.
Continue Mechanical Reasoning
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