Chapter 11Chapter 11MotionMotion

11.3 Acceleration11.3 Acceleration

How are changes in velocity How are changes in velocity described?described?

The rate at which velocity The rate at which velocity changes is called changes is called accelerationacceleration..

What Is Acceleration?

• Acceleration applies to any Acceleration applies to any change in an object’s velocity. change in an object’s velocity. • positive acceleration - positive acceleration -

increasing change in speed increasing change in speed • negative acceleration - negative acceleration -

decreasing change in speed. decreasing change in speed. Also called Also called DecelerationDeceleration

What Is Acceleration?

Free fallFree fall is the movement of an object is the movement of an object toward Earth solely because of gravity. toward Earth solely because of gravity.

• The unit for velocity = meters per The unit for velocity = meters per second. second.

• The unit for acceleration = meters The unit for acceleration = meters per second squared (m/sper second squared (m/s22). ).

Objects falling near Earth’s surface Objects falling near Earth’s surface accelerate downward at a rate of 9.8 accelerate downward at a rate of 9.8 m/sm/s22. .

What Is Acceleration?

Each second an Each second an object is in free fall, object is in free fall, its velocity its velocity increases increases downward by 9.8 downward by 9.8 meters per second. meters per second.

The change in the The change in the stone’s speed is 9.8 stone’s speed is 9.8 m/sm/s22, the , the acceleration due to acceleration due to gravity.gravity.

What Is Acceleration?

t = 0 sv = 0 m/s

t = 1 sv = 9.8 m/s

t = 2 sv = 19.6 m/s

t = 3 sv = 29.4 m/s

The velocity of an object moving in The velocity of an object moving in a straight line changes at a a straight line changes at a constant rate when the object is constant rate when the object is experiencing constant experiencing constant acceleration. acceleration.

• Constant accelerationConstant acceleration is a is a steady change in velocity.steady change in velocity.

What Is Acceleration?

Acceleration is the rate at which Acceleration is the rate at which velocity changes. velocity changes. VVii is the initial is the initial

velocity, velocity, vvff is the final velocity, and is the final velocity, and t t is is

total time. total time.

Calculating AccelerationCalculating Acceleration

A ball rolls down a ramp, starting A ball rolls down a ramp, starting from rest. After 2 seconds, its from rest. After 2 seconds, its velocity is 6 meters per second. velocity is 6 meters per second. What is the acceleration of the What is the acceleration of the ball?ball?

Calculating Acceleration

1.1. A car traveling at 10 m/s A car traveling at 10 m/s starts to decelerate steadily. It starts to decelerate steadily. It comes to a complete stop in 20 comes to a complete stop in 20 seconds. What is its seconds. What is its acceleration?acceleration?

2. 2. An airplane travels down a An airplane travels down a runway for 4.0 seconds with an runway for 4.0 seconds with an acceleration of 9.0 m/sacceleration of 9.0 m/s22. What is . What is its change in velocity during this its change in velocity during this time? time?

3. 3. A child drops a ball from a A child drops a ball from a bridge. The ball strikes the bridge. The ball strikes the water under the bridge 2.0 water under the bridge 2.0 seconds later. What is the seconds later. What is the velocity of the ball when it velocity of the ball when it strikes the water? strikes the water?

Describing Ionic Compounds

4. 4. A boy throws a rock straight A boy throws a rock straight up into the air. It reaches the up into the air. It reaches the highest point of its flight after highest point of its flight after 2.5 seconds. How fast was the 2.5 seconds. How fast was the rock going when it left the boy’s rock going when it left the boy’s hand? hand?

Acceleration ExampleAcceleration Example

A flowerpot falls off a second A flowerpot falls off a second story windowsill. It starts from story windowsill. It starts from rest and hits the sidewalk 1.5 s rest and hits the sidewalk 1.5 s later with a velocity of 14.7 m/s. later with a velocity of 14.7 m/s. Find the average acceleration of Find the average acceleration of the flowerpot.the flowerpot.

Acceleration PracticeAcceleration Practice

1.1. A skateboard accelerates from 0 A skateboard accelerates from 0 m/s to 4 m/s in 2.5 s.m/s to 4 m/s in 2.5 s.

2.2. A swimming turtle has a speed of A swimming turtle has a speed of 0.50 m/s. After 4 s, its speed is 0.50 m/s. After 4 s, its speed is 0.80 m/s.0.80 m/s.

3.3. A train slows down from 12 m/s A train slows down from 12 m/s to 9.6 m/s in 0.8 s.to 9.6 m/s in 0.8 s.

How does a speed-time graph How does a speed-time graph indicate acceleration?indicate acceleration? The slope of a speed-time The slope of a speed-time graph is acceleration.graph is acceleration.

Graphs of Accelerated Motion

Speed-Time GraphsSpeed-Time Graphs

Constant acceleration is Constant acceleration is represented on a speed–time graph represented on a speed–time graph by a straight line. The slope of the by a straight line. The slope of the line is the acceleration.line is the acceleration.

Graphs of Accelerated Motion

Distance-Time GraphsDistance-Time Graphs

Accelerated motion is represented Accelerated motion is represented by a curved line on a distance-by a curved line on a distance-time graph. time graph.

Graphs of Accelerated Motion

Graphing AccelerationGraphing Acceleration

0

1

2

3

0 2 4 6 8 10

Time (s)

Sp

ee

d (

m/s

)

Speed-Time GraphSpecify the time Specify the time

period when the period when the object was...object was...

slowing downslowing down

speeding upspeeding up

moving at a moving at a constant speedconstant speed

not movingnot moving

Acceleration ProblemAcceleration Problem

Timothy was playing ball in the Timothy was playing ball in the house when his ball bounced out house when his ball bounced out the window. A freely falling object the window. A freely falling object accelerates at 9.8 m/s/s. What is accelerates at 9.8 m/s/s. What is the velocity of Timothy’s ball after the velocity of Timothy’s ball after 2 s?2 s?

Instantaneous accelerationInstantaneous acceleration is how is how fast a velocity is changing at a fast a velocity is changing at a specific instant. specific instant.

Instantaneous Acceleration

Assessment Questions

1.1. What is acceleration? What is acceleration? a.a. the rate at which speed increasesthe rate at which speed increasesb.b. the time an object’s velocity the time an object’s velocity

increasesincreasesc.c. the rate at which displacement the rate at which displacement

changeschangesd.d. the rate at which velocity changesthe rate at which velocity changes

Assessment Questions

2.2. A sports car can accelerate from A sports car can accelerate from 0 m/s to 28 m/s in four seconds. 0 m/s to 28 m/s in four seconds. What is the acceleration of the car?What is the acceleration of the car?a.a. 24 s24 sb.b. 7 m/s7 m/sc.c. 27 m/s27 m/sd.d. 14 m/s14 m/s

Assessment Questions3.3. If you were to sketch a displacement-time If you were to sketch a displacement-time

graph and a speed-time graph for an object graph and a speed-time graph for an object experiencing constant acceleration, what experiencing constant acceleration, what would they look like? would they look like?

a.a. Both graphs would be linear, with the Both graphs would be linear, with the displacement-time graph being steeper.displacement-time graph being steeper.

b.b. Both graphs would be linear, with the speed-Both graphs would be linear, with the speed-time graph being steeper.time graph being steeper.

c.c. Both graphs would be nonlinear.Both graphs would be nonlinear.

d.d. The speed-time graph would be linear; the The speed-time graph would be linear; the displacement-time graph would be displacement-time graph would be nonlinear.nonlinear.

Assessment Questions

4.4. Which of the following is an example of Which of the following is an example of negative acceleration? negative acceleration?

a.a. Mike starts riding his bike and uses the Mike starts riding his bike and uses the pedals to go from 0 km/h to 20 km/h.pedals to go from 0 km/h to 20 km/h.

b.b. Mike pedals up a hill and gradually Mike pedals up a hill and gradually slows from 20 km/h to 5 km/h.slows from 20 km/h to 5 km/h.

c.c. Mike sits on his bike at the top of the Mike sits on his bike at the top of the hill and rests.hill and rests.

d.d. Mike coasts downhill without Mike coasts downhill without pedalling, going from 0 km/h to 15 pedalling, going from 0 km/h to 15 km/h.km/h.

Assessment Questions

5.5. The acceleration at a specific point The acceleration at a specific point on a distance-time graph is the on a distance-time graph is the

a.a. instantaneous acceleration.instantaneous acceleration.

b.b. momentary acceleration.momentary acceleration.

c.c. positive acceleration.positive acceleration.

d.d. numerical acceleration.numerical acceleration.

Assessment Questions

6.6. If an object experiences a steady If an object experiences a steady velocity change in a straight line, it velocity change in a straight line, it is undergoing constant acceleration.is undergoing constant acceleration.

TrueTrueFalseFalse