Speed and Acceleration Measuring motion. What Is Motion? Motion is when an object changes place or...

Speed and AccelerationMeasuring motion

What Is Motion?

Motion is when an object changes place or position. To properly describe motion, you need to use the following:

• Start and end position?• Movement relative to what?• How far did it go?• In what direction did it go?

Measuring Distance

Meter – international unit for measuring distance.

= 50 m1 mm

Calculating Speed

Speed (S) = distance traveled (d) / the amount of time it took (t).

Speed is the distance an object travels in a certain amount of time.

S = d/t

Units for speed

Depends, but will always be a distance unit / a time unit

Ex. Cars: mi./h Jets: km/h Snails: cm/s Falling objects: m/s

Calculating speed

If I travel 100 kilometer in one hour then I have a speed of…

100 km/h

If I travel 1 meter in 1 second then I have a speed of….

1 m/s

S = d/t

Ways To Calculate SpeedConstant speed is when you are traveling at the same rate of speed, such as 55 mph constantly on a highway.Average speed is taking the total distance traveled, and dividing by the total time it takes. Used for calculations that involve changing speed.Instantaneous speed is the speed at any one given point in time.

Average speed

Speed is usually NOT CONSTANT Ex. Cars stop and go regularly Runners go slower uphill than downhill

Average speed = total distance traveled/total time it took.

Average Speed What is the AVERAGE speed of

the bass boat depicted in the graph?

Bass Boat Speed

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65 65 65

85

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125

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Time (seconds)

Dis

tan

ce

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ete

rs)

Calculating Average Speed

It took me 1 hour to go 40 km on the highway. Then it took me 2 more hours to go 20 km using the streets.

Total Distance: 40 km + 20 km = 60 km

Total Time: 1 h + 2 h = 3 hr

Ave. Speed: total d/total t = 60 km/3 h = 20 km/h

timeTotal

DistTotalSpeedAve

_

.__.

Question

I travelled 25 km in 10 minutes. How many meters have I travelled? A) 25000 m B) .0112 m C) .025 m D) 2.5 m

25 km * 1000m/km = 25000 m

Question

I ran 1000 m in 3 minutes. Then ran another 1000 m uphill in 7 minutes. What is my average speed? A) 100 m/min B) 2000 m/min C) 10 m/min D) 200 m/min E) 20 m/min

Total Dist. = 1000 m + 1000 m = 2000 m

Total Time = 3 min + 7 min = 10 min

Ave speed = total dist/total time =

2000m/10 min = 200 m/min = D

Speed Graphs

• In what time period is the bass boat speeding up? • In what time period is the bass boat slowing down?• When is the speed NOT changing?

Bass Boat Speed

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Time (seconds)

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Instantaneous Speed

What is the instantaneous speed of the bass boat at t=7 seconds?

Instantaneous speed is speed at any given point in time. At 7 seconds, the distance is 85 meters; therefore the IS is

Graphing Speed

Speed is usually graphed using a line graph, and it depicts the distance and time.

•Time is the independent variable, and thus is ALWAYS on the x-axis.•Distance is the dependent variable, and is ALWAYS on the y-axis.

Velocity

Velocity – the SPEED and DIRECTION of an object.

Example: An airplane moving North at 500 mph A missile moving towards you at 200 m/s

Question

What is the difference between speed and velocity?

Speed is just distance/time. Velocity includes direction as well.

Velocity Problem

Indicate which of the following are velocities:

a. 125 cm/secb. 30 km/h northwestc. 350m/sec northd. 520 km/h

Graphing Speed: Distance vs. Time Graphs

Phoenix

Denver


3 h

600 km


3 minutes

600 m

Different Slopes

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Dis

tan

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km

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Run = 1 hr

Run = 1 hr

Run = 1 hr

Rise = 0 km

Rise = 2 km

Rise = 1 km

Slope = Rise/Run= 1 km/1 hr= 1 km/hr



Question

Below is a distance vs. time graph of my position during a race. What was my AVERAGE speed for the entire race?

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Time (hr)

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Average Speed = Total distance/Total time = 12 km/6 hr= 2 km/hr

Run = 6 hr

Rise = 12 km

Question

What does the slope of a distance vs. time graph show you about the motion of an object?

It tells you the SPEED

Question

Below is a distance vs. time graph for 3 runners. Who is the fastest?

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Time (h)

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mi.

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Bob

Jane

Leroy

Leroy is the fastest. He completed the race in 3 hours

Acceleration

Acceleration = speeding up

Acceleration – the rate at which velocity changes Can be an:

Increase in speed Decrease in speed Change in direction

Types of acceleration

Increasing speed Example: Car speeds up at green light

Decreasing speed Example: Car slows down at stop light Deceleration is when acceleration has a

negative value. Changing Direction

Example: Car takes turn (can be at constant speed)

screeeeech

Question

How can a car be accelerating if its speed is a constant 65 km/h?

If it is changing directions it is accelerating

Calculating Acceleration

If an object is moving in a straight line

Time

SpeedInitialspeedFinalonAccelerati

__

Units of acceleration:m/s2

Calculating Acceleration

0 s 1 s 2 s 3 s 4 s

0 m/s 4 m/s 8 m/s 12 m/s 16 m/s

2/4

4

/0/16

__

sm

s

smsmTime

SpeedInitialSpeedFinalonAccelerati

Question

A skydiver accelerates from 20 m/s to 40 m/s in 2 seconds. What is the skydiver’s average acceleration?

2/10

2

/20

2

/20/40

__

sm

s

sm

s

smsmTime

speedInitialspeedFinalAccel

A skateboarder is moving in a straight line at a speed of 3 m/s and comes to a stop in 2 sec. What is his acceleration?

Graphing Acceleration

Can use 2 kinds of graphs Speed vs. time Distance vs. time

Graphing Acceleration:Speed vs. Time Graphs

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1)Speed is increasing with time = accelerating2)Line is straight = acceleration is constant

Graphing Acceleration:Speed vs. Time Graphs

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1)In Speed vs. Time graphs:Acceleration = Rise/Run = 4 m/s ÷ 2 s = 2 m/s2

Run = 2 s

Rise = 4 m/s

Graphing Acceleration:Distance vs. Time Graphs

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1)On Distance vs. Time graphs a curved line means the object is accelerating.

2)Curved line also means your speed is increasing. Remember slope = speed.

Question

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m/s

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Above is a graph showing the speed of a car over time.1) How is the speed of the car changing (speeding up,

Slowing down, or staying the same)?2) What is this car’s acceleration?

1) The car is slowing down2) Acceleration = rise/run = -6m/s ÷3s = -2 m/s2

Run = 3 s

Rise = -6 m/s

Question:

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1)Which line represents an object that is accelerating?

The black and red lines represent a objects that are accelerating. Black is going a greater distance each second, so it must be speeding up. Red is going less each second, so must be slowing down

Remember: in distance vs. time graphs: curved line = accelerating, flat line = constant speed

Question: Hard one

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Above is a graph showing the speed of a car over time.1)What would a distance vs. time graph for thislook like?

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Time (s)

Dis

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m)

Speed and Acceleration Measuring motion. What Is Motion? Motion is when an object changes place or...

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