# Ch. 2. Motion is Relative Think about how fast you are moving when walking inside of a plane compared to walking across campus…

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Ch. 2

Motion is Relative Think about how fast you are moving when walking inside of a plane compared to walking across campus…

Speed A measure of how fast an object is moving Measured using distance covered in a unit of time speed = distance / time s = d/t

Instantaneous Speed = speed at a particular instance Average Speed = average speed during a trip average speed = total distance covered time interval

Velocity ( v ) Speed in a given direction v = d/t Velocity = distance covered per unit time What are the requirements for Constant Velocity? What are the requirements for Changing Velocity?

Velocity Speed in a given direction What are the requirements for Constant Velocity? Requires BOTH constant speed and direction What are the requirements for Changing Velocity? – Changing speed – Changing direction OR BOTH!!!!!

Acceleration (a) The rate at which velocity is changing a =  v t

Acceleration (a) The rate at which velocity is changing a =  v = v final – v initial tt

Problem Solving Strategies Memorize the variables that are given in each equation!!!! – example: v = velocity Know the units for a given variable – example: velocity is measured in units of distance over time (meters per second or m/s)

Journal Velocity (v) v = d/t Units: m/s Acceleration (a) a = v f -v i t Units: m/s 2

Journal: Problem Solving Practice 1. You ride a bike a distance of 6 m in 2 s. What is your speed?

Problem Solving Practice 1. You ride a bike a distance of 6 m in 2 s. What is your speed? s = d/t

Problem Solving Practice 1. You ride a bike a distance of 6 m in 2 s. What is your speed? s = d/t s = 6 m/ 2s

Problem Solving Practice 1. You ride a bike a distance of 6 m in 2 s. What is your speed? s = d/t s = 6 m/ 2s s = 3 m/s

2. A car moving in a straight line increases its speed from 70 km/h to 75 km/h in 5 seconds. What is the acceleration of the vehicle? a =  v/t

2. A car moving in a straight line increases its speed from 70 km/h to 75 km/h in 5 seconds. What is the acceleration of the vehicle? a =  v/t a = 75 – 70 5

2. A car moving in a straight line increases its speed from 70 km/h to 75 km/h in 5 seconds. What is the acceleration of the vehicle? a =  v/t a = 75 – 70 = 5 = 1 km/ h  s 5 5

3. You yell across a canyon and you hear your echo return 6.5 s later. Assuming that the speed of sound in air is 340 m/s. How wide is the canyon at this location? equation:

3. You yell across a canyon and you hear your echo return 6.5 s later. Assuming that the speed of sound in air is 340 m/s. How wide is the canyon at this location? equation: v = d/t rearrange to get d = v  t Since we are solving for the width…..

3. You yell across a canyon and you hear your echo return 6.5 s later. Assuming that the speed of sound in air is 340 m/s. How wide is the canyon at this location? equation: v = d/t rearrange to get d = v  t Since we are solving for the width, not the entire journey, we need to only use half the time. Plug and Chug

3. You yell across a canyon and you hear your echo return 6.5 s later. Assuming that the speed of sound in air is 340 m/s. How wide is the canyon at this location? equation: v = d/t rearrange to get d = v  t Since we are solving for the width, not the entire journey, we need to only use half the time. d = (340 m/s) (3.25 s) = 1105 m

More Practice 4. What is the acceleration of a car moving in a straight path that increases its speed from 5 km/h to 17 km/h in 3 seconds? 5. By how much does the speed of a vehicle moving in a straight line change each second when it is accelerating at 3 km/h  s? 6. Calculate the average speed of a skateboarder that covers 20 m in 5 seconds?

More Practice 4. What is the acceleration of a car moving in a straight path that increases its speed from 5 km/h to 17 km/h in 3 seconds? 4 km/h  s 5. By how much does the speed of a vehicle moving in a straight line change each second when it is accelerating at 3 km/h  s? 3 km/h 6. Calculate the average speed of a skateboarder that covers 20 m in 5 seconds? 4 m/s

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