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.
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
Graphing SpeedGraphing Speed
• Distance on the Y-axis
• Time on the X-axis
• Title your graphs correctly
• Label your axes correctly
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