Constant Motion

Constant Motion

Unit 1 - Kinematics

Constant means "unchanging over time."

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​"Constant"

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Multiple Choice

Which one of the choices below is always "constant"?

• hair length

• time

• your pant size after quarantine

• your grade in Physics

Are speed and velocity the same thing?

NO!

Speed is the rate that a certain distance is covered over time.

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Speed is scalar.​ It tells us only the magnitude of how fast an object is moving.

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The SI unit for speed is meters per second (m/s)​

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Speed

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Velocity is the rate of displacement that is covered over time.

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Velocity is a vector.​ It tells us both the magnitude (speed) and direction of an object's motion.

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The SI unit for velocity is meters per second (m/s)​

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Velocity

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Multiple Choice

A brand new car has an odometer reading of 10,000 meters after 45 minutes of driving. What was the average speed of the car?

• 2.9 m/s

• 4 m/s

• 15 m/s

• 222 m/s

Multiple Choice

What was the record time of Usain Bolt during the 100-m event in 2009 if he ran 10.44 m/s?

• 1000 seconds

• 1044 seconds

• 10 seconds

• 8 seconds

Constant speed and velocity

So if constant means "unchanging"...

Then constant speed or constant velocity means that an object's speed or velocity is not changing over time.

Any changes in an object's position over time can be graphed with position on the y-axis and time on the x-axis.

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​Position vs time graph

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The slope of a position vs time graph for an object experiencing constant motion is linear (a straight line).

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​Position vs time graph

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The slope of a linear graph can be calculated with rise over run.

Slope of an x-t graph

For a position vs time graph, the slope of the line represents the velocity of an object!

Slope of an x-t graph

Describing the Motion

Object is moving in a positive direction ​away from the origin with a constant positive velocity.

​Object is at rest at a positive position away from the origin.

​Object is moving in a negative direction towards the origin with a constant negative velocity.

Describing the Motion

Multiple Choice

Which time segment shows the object at rest?

• 10-15 seconds

• 30 seconds

• 15-40 seconds

• 55 seconds

Multiple Choice

When is the object moving with a negative velocity towards the origin?

• 15 - 40 seconds

• 15 - 30 seconds

• 40 5

• 55 seconds

Multiple Choice

Which cyclist is constantly moving away from their starting place?

• A

• B

• C

• D

Multiple Choice

The graphs show 4 cyclists on an afternoon ride. Which cyclist stops for a water break during their ride?

• A

• B

• C

• D

Multiple Select

Which two cyclists are going the same speed?

• A

• B

• C

• D

Multiple Select

Which two cyclists are going the same velocity?

• None

• B

• C

• D

Multiple Select

Which cyclist(s) have a displacement of 0m?

• A

• B

• C

• D

Multiple Choice

Which cyclist(s) have traveled the farthest total distance?

• A

• B

• C

• D