Kinematics · AP Physics 1

Acceleration

Accelerating vs. Decelerating

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Do Now warm-up prompt

Acceleration - time rate of change in velocity (how quickly velocity is changing)

Distance and Motion

Distance and Motion - Flash

Ranking Task

Which car has the greater acceleration?

t (sec)012345
Car A70 m/s72 m/s74 m/s76 m/s78 m/s80 m/s
Car B0 m/s3 m/s6 m/s9 m/s12 m/s15 m/s
Car C90 m/s90 m/s90 m/s90 m/s90 m/s90 m/s
Car D100 m/s99 m/s98 m/s97 m/s96 m/s95 m/s
↓

Acceleration of Each Car

Car A: +2 m/s²
Car B: +3 m/s²
Car C: 0 m/s²
Car D: −1 m/s²

2 Ways to Have Zero Acceleration

a) Remain at Rest

Eskimo standing still while ice skating

b) Constant Velocity

Boy skateboarding at a constant velocity

1. Equation

a = ΔV/Δt = (Vf − Vi)/t

Ex 1

Action hero being chased by a helicopter
Given

Starting Velocity: 80 km/h West
Final Velocity: 110 km/h West
Acceleration: 1.6 m/s²
Find: How long did it accelerate?

↓

(Vf − Vi) = 30 km/h W →
convert: 30 km/h × (1000 m/km) × (1 h/3600 s) ≈ 8 m/s

a = (Vf − Vi)/t →
1.6 m/s² = (8 m/s)/t

t = 5 sec

Accelerating or Decelerating?

An object has an acceleration of −12 m/s². Is it accelerating or decelerating? It depends on the sign of the velocity.

Accelerating

If velocity is negative: −100 m/s to −124 m/s in 2 sec

Decelerating

If velocity is positive: 124 m/s to 100 m/s in 2 sec

CaseVelocity SignAcceleration Sign
AcceleratingV+A+
AcceleratingV−A−
DeceleratingV+A−
DeceleratingV−A+
Man bending over backwards
Object is said to be “Accelerating Backwards” — the force required to slow an object always opposes the object's motion.

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