ACCELERATIONACCELERATION

Science 10 – Physics UnitScience 10 – Physics Unit

Comparing Types of MotionComparing Types of Motion

• Uniform motion– Moves in a straight line with constant velocity

•Speed and direction are constant•Feels smooth or like no motion is occurring

• Non-uniform motion -- acceleration– Speed and/or direction is changing

•Feels like being pushed or pulled

ACCELERATIONACCELERATION

•Acceleration is a rate (over time) of change in velocity

•Occurs whenever–Speed changes–Direction changes

ACCELERATIONACCELERATION• Acceleration (a) is calculated as

• a = ∆ v = v2 – v1 change in velocity

∆t = t2 – t1 change in time

• Acceleration units are derived from velocity units (m/s) over time units (s)

• Acceleration units are m/s/s = m/s2

a = Δv = m/s Δt s

a = Δv Δt

Equation ManipulationEquation Manipulation

Δt = tf – ti

Δt + ti

tf – Δt

Δv = vf – vi

Δv + vi

vf – Δv

a = Δv Δt

a Δt

Δv a

tf =

ti =vi =

vf = Δv =

Δt =

a = vf – vi

tf – ti

vf – vi = a (tf – ti)

ti = tf = vf – vi

a

a = Δv Δt

Δv = a Δt

Δt = Δv a

Equation ManipulationEquation Manipulation

Practice Practice unit unit recognitionrecognition

Measurement

• 25m

• 25s

• 25m/s

• 25m/s2

Property

Time

Velocity

Acceleration

Position

AccelerationAcceleration

• BIG Acceleration means velocity is

CHANGING QUICKLY

– Means speed changes in short time

interval

– Means direction changes in short time

interval

– DOES NOT MEAN big velocity

AccelerationAcceleration

• Small Acceleration means velocity is

CHANGING SLOWLY

– Means speed changes in long time

interval

– Means direction changes in long time

interval

– DOES NOT MEAN small velocity

Comparing AccelerationsComparing Accelerations

• Instantaneous acceleration – acceleration at a specific moment in time (*snaps)

• Average acceleration – acceleration which occurs over a time interval

• When acceleration is constant, – average equals instantaneous

Comparing AccelerationsComparing Accelerations

• Positive Acceleration means

velocity is INCREASING

–more speed over time

–away from origin over time

Comparing AccelerationsComparing Accelerations

• Negative Acceleration means

velocity is DECREASING

–less speed over time

–toward origin over time

Check Your Understanding:Check Your Understanding:

Which measurement is an acceleration?

(a) 25s(b) 25m/s(c) 25m/s/s(d) 25m

Which measurement shows greatest acceleration?

(a) 25m/s 5s

(b) 25m/s 2s

(c) 25m/s 10s

(d) 25m/s 25s

UNITS!Smallest

time interval

Comparing ConstantsComparing Constants

Constant “velocity” vs Constant “acceleration”

• Constant velocity = no change in velocity – acceleration = ZERO

• Constant acceleration = no change in rate of velocity– Velocity is changing at a constant rate

Visualizing AccelerationVisualizing Acceleration• metronome and marker (ticker timer)

Positive acceleration

•• • • • • – more distance in same time, increasing velocityNegative acceleration

• • • • • •– Less distance in same time, decreasing velocity

Visualizing AccelerationVisualizing Acceleration

• Velocity-Time Graphs – effect of time on velocity – Velocity labeled on y-axis– Time labeled on x-axis

• Slope (line) represents acceleration• The steeper the slope, the greater

acceleration – the greater the CHANGE IN velocity

Time(s)

Velocity

(m/s)

0 10

1 10

2 10

3 10

4 10

5 10

Flat line represents ZERO acceleration Flat line represents ZERO acceleration – zero change in velocity --- constant – zero change in velocity --- constant

velocityvelocity

Time(s)

Velocity

(m/s)

0 0

1 10

2 20

3 30

4 40

5 50

Smooth sloping line upward Smooth sloping line upward represents increasing velocityrepresents increasing velocity

Smooth sloping line downward Smooth sloping line downward represents decreasing velocityrepresents decreasing velocity

Time(s)

Velocity(m/s)

0 50

1 40

2 30

3 20

4 10

5 0

a = - 10m/s2 = slope

Ve

loci

ty (

m/s

)

time (s)

Curved slope means changing Curved slope means changing accelerationacceleration

A. At which time interval is acceleration greatest?

B. At which time interval is acceleration zero?

C.How long does it take the object to slow to a stop?

D.What is the Δv of the blue line between 1s & 2s?

0-2s

4-7s

3s

Practice Analysis

5m/s

A. Which line shows negative acceleration?

B. Which line shows zero acceleration?

C.Which line shows greatest constant acceleration?

D.Which line shows changing acceleration?

Blue (A)

Blue (A)

Purple (C)

Practice Analysis

E

(E)

Calculating accelerationCalculating acceleration

a = vf – vi

tf – ti

Suppose a car going in a straight Suppose a car going in a straight line is moving at 35km/hr at 3 line is moving at 35km/hr at 3 seconds and 50km/h at 8 seconds. seconds and 50km/h at 8 seconds. What is the accelerationWhat is the acceleration of the car? of the car?

Given Unknown Equation Solution Sentence

Calculating accelerationCalculating acceleration

a = vf – vi

Δt

What is the accelerationWhat is the acceleration of a of a vehicle that changes its velocity vehicle that changes its velocity from 100 km/h to a dead stop in from 100 km/h to a dead stop in 10s?10s?

G U E S S

Calculating time intervalCalculating time interval

a = vf – vi

Δt

When the shuttle bus comes to a sudden When the shuttle bus comes to a sudden stop to avoid hitting a dog, it accelerates stop to avoid hitting a dog, it accelerates uniformly at 4.1m/suniformly at 4.1m/s22 as it slows from 9.0m/s to as it slows from 9.0m/s to 0m/s. 0m/s. FindFind the the time intervaltime interval of acceleration for of acceleration for the bus.the bus.

G U E S S

Δt = vf – vi

avf – vi = aΔt