Kinematics

Acceleration

How Quickly Velocity Changes

← Velocity All Lessons Word Problems →
Do Now warm-up prompt

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

Fill In The Blank Notes

Warm-Up

What is the motion word that describes how quickly an object changes its velocity?

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See Acceleration in Action

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Video Instruction

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Enduring Understanding

1. Acceleration is the time rate of change in velocity. Includes direction.

2. There are 3 ways to accelerate — speed up, slow down, and change direction.

Ranking Task

Rank the accelerations below from smallest to greatest.

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: 5 m/s West
Final Velocity: 25 m/s West
Time: 5 sec

↓

a = (Vf − Vi) / t
= 20 m/s West / 5 sec

a = 4 m/s² West

Ex 2

Girl running with a stick
Given

Starting Velocity: 20 m/s West
Final Velocity: 5 m/s West
Time: 5 sec

↓

a = (Vf − Vi) / t
= −15 m/s West / 5 sec

a = −3 m/s² West (3 m/s² East)

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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Check Your Understanding

5 quick questions — pick an answer to see if you’re right.

1. What is acceleration?

2. A car drives around a curve at a steady 20 m/s. Is it accelerating?

3. A car speeds up from 10 m/s east to 30 m/s east in 5 s. What is its acceleration?

4. A runner slows from 20 m/s west to 5 m/s west in 5 s. What is the acceleration?

5. A car's speedometer reads 90 m/s every second for 5 s while it drives in a straight line. What is its acceleration?

Word Problems →