LucidSTEM
A-LEVEL 9702 · AS · TOPIC 2
Kinematics.
The chain of the topic: define displacement, velocity and acceleration, read them off motion graphs as gradients and areas, fold them into the four SUVAT equations, apply those to free fall under gravity, then split a projectile into two independent perpendicular motions. Around the hexagon are the four ideas; above is what it builds on, below is where it leads, to motion explained by forces.
TOPIC 2: KINEMATICS
CAMBRIDGE A-LEVEL PHYSICS 9702 · PATHWAYS
TheLucidSTEM · thelucidstem.com
BUILDS ON
T1 Quantities, units & vectors T3 Dynamics (returns: F = ma) 2.1
2.1
2.1
2.1
TOPIC 2
KINEMATICS
motion described
1 · DESCRIBING MOTION & GRAPHS
Position, its rate of change, and its rate of change.
Displacement s is a vector; distance is its scalar length
Velocity v = Δs / Δt; acceleration a = Δv / Δt
Gradient of s vs t gives v; gradient of v vs t gives a
Area under a v vs t graph gives displacement s
v = ds/dt a = dv/dt
v
t
area = s
gradient = a
2 · EQUATIONS OF MOTION (SUVAT)
Constant acceleration: four equations, five symbols.
Valid only when a is uniform; s, u, v, a, t are the five
List what you know; pick the equation missing the
unknown you do not need.
They follow from the v vs t graph: gradient and area
v = u + at s = ½(u + v)t
s = ut + ½at² v² = u² + 2as
v
t
u
v
t
s = area
3 · FREE FALL UNDER GRAVITY
The special case: a = g, directed downward.
With no air resistance every body falls with the same g
Near Earth g ≈ 9.81 m s−², taken as the only force
Released from rest: s = ½gt², v = gt
Measure g by timing a steel ball dropped a height s
g = 2s / t²
g
equal time steps
gaps grow: speeding up
4 · PROJECTILE MOTION
Two independent motions, one parabola.
Horizontal: constant velocity, no force (ignore drag)
Vertical: free fall, acceleration g, exactly as section 3
The two share only the same clock t; solve separately
Resolve the launch u: horizontal u cosθ, vertical u sinθ
x = (u cosθ) t y = (u sinθ) t − ½gt²
y
x
vx
vy
vx constant; vy changes
LEADS TO
T3 Dynamics: acceleration explained by F = ma T5 Energy: work and power from v and a T12 Circular motion: a from a turning velocity Kinematics describes how things move; the rest of mechanics asks why, by adding the forces that cause the acceleration.
← Builds on IGCSE: Motion