Bell RingerBell Ringer 1-13-1-13-1010

1.1. Give me an example of a unit that Give me an example of a unit that measures distance.measures distance.

2.2. What What ALWAYSALWAYS needs to go at the top of needs to go at the top of your graph?your graph?

3.3. What is the formula for acceleration?What is the formula for acceleration?4.4. A football field is about 100 meters long. A football field is about 100 meters long.

If it takes a person 20 seconds to run its If it takes a person 20 seconds to run its length, what is the speed of the runner?length, what is the speed of the runner?(You may use your formula sheet.)(You may use your formula sheet.)

More Speed ProblemsMore Speed Problems1.1. The pitcher’s mound in baseball is 85 m The pitcher’s mound in baseball is 85 m

from the plate. It takes 4 seconds for a from the plate. It takes 4 seconds for a pitch to reach the plate. How fast is the pitch to reach the plate. How fast is the pitch?pitch?

2.2. A runner covers a distance of 120 m in a A runner covers a distance of 120 m in a time of 80 seconds. What is the runner’s time of 80 seconds. What is the runner’s speed?speed?

ObjectivesObjectivesALCOS Objective # 1ALCOS Objective # 1

Identify steps within the scientific Identify steps within the scientific processprocessApplying process skills to interpret Applying process skills to interpret

data from graphs.data from graphs.ALCOS Objective # 8ALCOS Objective # 8

Identify Newton’s three laws of Identify Newton’s three laws of motion.motion.

AccelerationAccelerationChapter 9, Section 3Chapter 9, Section 3

What is acceleration?What is acceleration?AccelerationAcceleration is the rate at is the rate at

which velocity changes.which velocity changes.In other words, acceleration In other words, acceleration

means “the process of means “the process of speeding up.”speeding up.”

Recall…Recall…What is velocity?What is velocity?Velocity describes both speed Velocity describes both speed

and direction.and direction.In science, acceleration refers In science, acceleration refers

to increasing speed, to increasing speed, decreasing speed, or changing decreasing speed, or changing direction.direction.

When an object speeds up, it is When an object speeds up, it is accelerating.accelerating.

When an object slows down, it is When an object slows down, it is known as deceleration. (or known as deceleration. (or negative acceleration)negative acceleration)

FormulaFormula If direction stays the same…If direction stays the same…

Acceleration = Acceleration = change in speedchange in speed timetime

Acceleration = Acceleration = Final speed – initial Final speed – initial speedspeed timetime

What are the units?What are the units?

If speed is measured in m/s, If speed is measured in m/s, acceleration is measured in acceleration is measured in m/sm/s22..

Calculating AccelerationCalculating AccelerationAccelerationAccelerationAs a roller coaster car starts down a As a roller coaster car starts down a

slope, its speed is 4 m/s. But 3 slope, its speed is 4 m/s. But 3 seconds later, at the bottom, its seconds later, at the bottom, its speed is 22 m/s. What is its average speed is 22 m/s. What is its average acceleration?acceleration?

Distance-time graphsDistance-time graphs On your paper, graph the following:On your paper, graph the following:

D (m)D (m) T (sec) T (sec) 00 00 55 77 1010 14 14 1515 21 21

Was your graph a straight line?Was your graph a straight line?A A distance-time graphdistance-time graph which is a which is a

straight linestraight line indicates indicates constant constant speedspeed..

In constant speed, the object In constant speed, the object does not speed up or slow down. does not speed up or slow down. The acceleration is zero.The acceleration is zero.

Graph the following on a Graph the following on a distance-time graph:distance-time graph:

D (m)D (m) T (s)T (s) 00 00 55 112020 224545 338080 44125125 55

0 1 2 3 4 5

Was your graph a curve?Was your graph a curve?A graph that A graph that curvescurves on a on a

distance-time graphdistance-time graph shows shows that the object is that the object is accelerating.accelerating.

Distance-time graphsDistance-time graphsDescribe the motion of the object as Describe the motion of the object as

shown in the shown in the graph.graph.From 0-8 sec, constant speed:(25 m/sec);From 8-12 sec, no motion;From 12-16 sec, acceleration;From 16-20 sec, constant speed

Speed-time graphsSpeed-time graphsUsing the distance-time graph from Using the distance-time graph from

the last frame, draw a speed time the last frame, draw a speed time graph. First fill in the table below:graph. First fill in the table below:

Average Speed (m/s)Average Speed (m/s) Time (sec) Time (sec) ________ 0 to 80 to 8________ 8 to 128 to 12________ 12 to 2012 to 20

250

37.5

What does your graph look What does your graph look like?like?

Constant speedConstant speed will be a will be a horizontal horizontal line line on a speed time graph. on a speed time graph.

If the speed If the speed decreasesdecreases, the line will , the line will

slant slant downdown..

If the speed If the speed increasesincreases, the line will slant , the line will slant upup..

What do the following speed-What do the following speed-time graphs depict?time graphs depict?

AccelerationAccelerationChange in velocityChange in velocity

Can be change in speed Can be change in speed oror direction direction

Acceleration = ∆V/ ∆TAcceleration = ∆V/ ∆T

∆ ∆VV aa tt

Acceleration problemAcceleration problem A roller coaster’s A roller coaster’s

velocity at the top velocity at the top of a hill is 10m/s. of a hill is 10m/s. Two seconds later Two seconds later it reaches the it reaches the bottom of the hill bottom of the hill with a velocity of with a velocity of 26m/s. What is the 26m/s. What is the acceleration of the acceleration of the roller coaster?roller coaster?

AnswerAnswerAcceleration = ∆V/ ∆TAcceleration = ∆V/ ∆Ta = a = 26m/s – 10m/s26m/s – 10m/s

2 s2 sa = a = 16m/s16m/s

2s2sa = 8m/s/s or 8m/sa = 8m/s/s or 8m/s22

Calculating AccelerationCalculating Acceleration

More acceleration problemsMore acceleration problems 1. A car accelerates at a rate of 1. A car accelerates at a rate of

20mi/hr/s. How long does it take to 20mi/hr/s. How long does it take to reach a speed of 80 mi/hr?reach a speed of 80 mi/hr?

2. A car travels at 60 miles per hour 2. A car travels at 60 miles per hour around a curve. Is the car accelerating?around a curve. Is the car accelerating?

3. A car travels in a straight line at 3. A car travels in a straight line at 60mi/hr. Is the car accelerating?60mi/hr. Is the car accelerating?

Answers:Answers:1. 1. ∆V ∆V 80mi/hr80mi/hr

a ta t 20mi/hr/s20mi/hr/s t t

4sec = t4sec = t2. Yes! Because it’s changing direction!2. Yes! Because it’s changing direction!3. No! It’s not changing speed or direction!3. No! It’s not changing speed or direction!

DecelerationDecelerationNegative accelerationNegative acceleration

Example: A car slows from Example: A car slows from 60mi/hr to 20mi/hr in 4 60mi/hr to 20mi/hr in 4 seconds. What is its seconds. What is its acceleration?acceleration?

Answer:Answer:Acceleration = ∆V/ ∆TAcceleration = ∆V/ ∆TAcceleration = Acceleration = Vf – ViVf – Vi

tta = a = 20mi/hr – 60mi/hr20mi/hr – 60mi/hr

4 s4 sa = a = -40mi/hr-40mi/hr

4s4sa = -10mi/hr/sa = -10mi/hr/s

Review: Distance-time graph of Review: Distance-time graph of accelerationacceleration

Distance-time graph of Distance-time graph of decelerationdeceleration

Review: Speed-time graph of Review: Speed-time graph of accelerationacceleration

Review: Speed-time graph of Review: Speed-time graph of decelerationdeceleration

Review: Distance-time graph of Review: Distance-time graph of constant speedconstant speed

Exit QuizExit Quiz 1-13-101-13-101.1. What is on the y-axis on a distance-What is on the y-axis on a distance-

time graph?time graph?2.2. What is constant speed in your own What is constant speed in your own

words?words?3.3. What does acceleration mean?What does acceleration mean?4.4. If acceleration is negative, what is it If acceleration is negative, what is it

called?called?5.5. If a car goes 20 meters in 5 If a car goes 20 meters in 5

seconds, what is its seconds, what is its speedspeed? ? (Include units!)(Include units!)