MotionMotion

Three Terms to know:

• Position. This is precisely where an object is located.

• Speed. Precisely how fast an object is moving.

• Acceleration. Precisely how fast an object's speed is changing. (most challenging for people)

What is Motion?What is Motion?

• Motion can be describedas a change in position.

• To know whether theposition of somethinghas changed, you needa reference point. (Train Example)

Motion and TimeMotion and Time

• Descriptions of motion often include speed

• If you think of motionmotion as a change in position, then speedspeed is an expression of how much time it takes for that change in position to occur

Speed…more definitionsSpeed…more definitions

• Speed is the rate of change in position.

• Speed can also be described as simply a “rate of motion”

Measuring SpeedMeasuring Speed

• The speedometer in a car shows instantaneous speed

• Instantaneous speed is the rate of motion at any given instant.

Average vs. Instantaneous Speed

Speed Triangle/Pyramid

The EquationsThe Equations

• DistanceDistance = = Speed Speed xx TimeTime

• SpeedSpeed = = DistanceDistance / / TimeTime

• TimeTime = = DistanceDistance / / SpeedSpeed

Changing SpeedChanging Speed• Think about riding a bicycle to your friends house

2 km away • You start from a stop. Speed = 0 km/hr• You reach a speed of 20 km/hr• As you pedal up a steep hill your speed drops to 12 km/hr• As you go down the hill your speed increases to 35 km/hr,

and you pull into your friend’s driveway• You look at your watch and see the trip has taken you

30 minutes• How would you express your speed on such a trip?

Would you use your fastest time, your slowest time, or some speed in between?

Average SpeedAverage Speed

• In cases where the rate of motion (speed) varies a great deal, the best way to describe speed is to use average speed.

• Average Speed is the total distance traveled divided by total time of travel

• So from the last slide: If the total distance was 2 km, and the total time was 30 minutes how fast was the cyclist going?

Example ProblemExample Problem• Your neighbor says she can skate at a speed

of 4 m/s. To see if you can skate faster, she times you as you skate as fast as you can for 100 m.

• Your time is 20 seconds. Who skates faster?

AnswerAnswer1. What is known/given?

DistanceDistance, d = 100m , d = 100m TimeTime, t = 20s, t = 20s2. What is unknown? (what are you trying to find?)

Average Speed = ?3. Choose an equation with the appropriate variables

ss = = dd / / tt4. Input the values and solve the equation

ss = = 100m100m / / 20 seconds20 seconds = = 5 m/s5 m/s

Velocity

• Speed with a direction…– 2 m/s SOUTH– 5.6 km/s NORTHWEST

Graphing SpeedGraphing Speed

• Distance on the Y-axis

• Time on the X-axis

• Title your graphs correctly

• Label your axes correctly

Distance Vs. Time

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Time (seconds)

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Time Distance0 01 12 23 34 45 56 67 78 89 9

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