physics chapter 2 lesson 2

Motion in One Dimension Section 2

© Houghton Mifflin Harcourt Publishing Company

What do you think?

• Which of the following cars is accelerating?– A car shortly after a stoplight turns green– A car approaching a red light– A car with the cruise control set at 80 km/h– A car turning a curve at a constant speed

• Based on your answers, what is your definition of acceleration?



Acceleration

• Rate of change in velocity• What are the units?

– SI Units: (m/s)/s or m/s2

– Other Units: (km/h)/s or (mi/h)/s

• Acceleration = 0 implies a constant velocity (or rest)



Classroom Practice Problem

• Find the acceleration of an amusement park ride that falls from rest to a velocity of 28 m/s downward in 3.0 s.– Answer: 9.3 m/s2 downward



Direction of AccelerationDescribe the motion of an object with

vi and a as shown to the left.

• Moving right as it speeds up

• Moving right as it slows down

• Moving left as it speeds up

• Moving left as it slows down

Vi a

+ +

+ -

- -

- +



Graphing Velocity

• The slope (rise/run) of a velocity/time graph is the acceleration.– Rise is change in v– Run is change in t

• This graph shows a constant acceleration.

• Average speed is the midpoint.

2i f

avg

v vv



Graph of v vs. t for a train

• Describe the motion at points A, B, and C.

• Answers– A: accelerating (increasing

velocity/slope) to the right– B: constant velocity to the right– C: negative acceleration

(decreasing velocity/slope) and still moving to the right



Useful Equations

1.

2.

3.

4.

5.

2i f

avg

v vv

avg

xv

t

avg

va

t

f iv v a t

21

2ix v t a t

2 2 2f iv v a x



Classroom Practice Problems

• A bicyclist accelerates from 5.0 m/s to 16 m/s in 8.0 s. Assuming uniform acceleration, what distance does the bicyclist travel during this time interval?– Answer: 84 m

• An aircraft has a landing speed of 83.9 m/s. The landing area of an aircraft carrier is 195 m long. What is the minimum uniform acceleration required for safe landing?– Answer: -18.0 m/s2



Now what do you think?

• Which of the following cars is accelerating?– A car shortly after a stoplight turns green– A car approaching a red light– A car with the cruise control set at 80 km/h– A car turning a curve at a constant speed

• Based on your answers, what is the definition of acceleration?• How is acceleration calculated?• What are the SI units for acceleration?

physics chapter 2 lesson 2

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