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LearnEdexcelYMA012018 specificationWME01 · Mechanics 1Dynamics of a particle in a straight line

WME01 · Module

Dynamics of a particle in a straight line

4 subtopics≈ 150 min in total

Start the module: Newton's laws and F = ma Open graphing calculator

Newton's laws and F = ma
Add up the forces in the direction of motion to get the resultant, then $F=ma$ gives the acceleration. If the resultant is zero, the object keeps a constant velocity. In lifts, the floor's reaction is more than the weight when accelerating upwards and less when accelerating downwards.
≈ 35 min
Friction and inclined planes
Friction opposes motion (or attempted motion) and can grow up to $\mu R$ . Once sliding, it equals $\mu R$ . On a slope, resolve along and perpendicular to the plane: the weight gives $mg\sin\theta$ down the slope and $mg\cos\theta$ into it, so $R=mg\cos\theta$ when nothing else pushes.
≈ 40 min
Connected particles and pulleys
Particles joined by a light inextensible string share the same acceleration, and a light string over a smooth pulley has the same tension on both sides. Write $F=ma$ for each particle separately; adding the equations eliminates the tension and gives $a$ .
≈ 40 min
Momentum and impulse
Momentum is mass × velocity, so it has a direction. An impulse changes momentum: $I=mv-mu=Ft$ . When two particles collide, the total momentum before equals the total after, as long as no external impulse acts.
≈ 35 min