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My, how you have changed! Acceleration 1

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Opening questions Was the motion of your MPV constant throughout its run? Suppose you walked at 3 miles/hour around a circular path at school. Is your rate of motion changing? Explain your response

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**What do the main subjects in the following pictures have in common about their motion?**

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They are accelerating 4

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Acceleration’s DEFINITION AND UNITS

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Acceleration Anytime the velocity of an object changes, the object accelerates Get Faster Get Slower If the motion of object changes direction, but stays at a constant rate 6

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Velocity changes if… Speeding up Slowing down 7

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Velocity changes if… The direction of the motion changes, but the speed does not This type of acceleration is call centripetal acceleration 8

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**Units for acceleration**

m/s2 (m/s) / s because the velocity (m/s) changes over time (s)

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**The proof of why it is like it is**

Derivation of units The proof of why it is like it is

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**How we get m/s2 for units of acceleration**

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Units How do you simplify (¾) / 9 12

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answer 13

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TYPES OF ACCELERATION

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**Average or overall Acceleration**

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**Average or overall acceleration**

Acceleration of an object determined over a certain time period

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**Calculating average/overall acceleration**

Acceleration = change in velocity / time a = ∆v / t 17

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**∆v ∆v = vf - vi The ∆ means the change in…**

So ∆v means change in velocity You find the change in a value by subtracting it initial value from its final value ∆v = final velocity – initial velocity ∆v = vf vi 18

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**Final Equation for average/overall acceleration**

a = (vf - vi) / t vf = final velocity vi = initial velocity t = elapsed time a = acceleration 19

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Ex #1 A flowerpot falls off a second story windowsill. The flowerpot start from rest and hits the sidewalk 1.5 s later with a velocity of 14.7m/s. Find the average acceleration. 20

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**What information is given? Identify the information.**

Is the time 14.7 m/s is the final velocity Starts from rest Means that the initial velocity is zero (0) “at rest” always means that vi = o 21

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**Answer #1 a = (14.7 – 0) / 1.5 = 9.8 What are the units?**

(14.7 m/s – 0 m/s) 1.5 s = (m/s) / s m / s2 22

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**UNIFORM OR CONSTANT ACCELERATION**

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**Constant acceleration**

Occurs when rate of change in the velocity of an object is constant. This means the velocity values change at the same rate each second An object that accelerates at 3 m/s2, goes from rest (0 m/s) to: 3 m/s after 1 second, 6 m/s after 2 sec, 9 m/s after 3 sec… 24

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**Constant acceleration and the graphs**

Constant acceleration is indicated by a smooth curve on a P-t graph, and a straight line on a V-t graph. Slope of the line on a V-t graph = value of constant acceleration

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**Ex What is the acceleration of the object at 5 min?**

What is the acceleration of the object at any time between 15 min and 40 min?

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**Constant Acceleration**

An object moving at a constant velocity has a constant acceleration of zero As evidenced in a graph by a straight horizontal line 27

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**Positive acceleration**

Positive slope of V-t graph, graph gets higher moving left to right Getting faster in the positive direction Getting slower in the negative direction 28

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**Negative acceleration**

Graph gets lower moving left to right Slowing down in the positive direction Speeding up in the negative direction 29

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Question What is the difference between constant velocity and constant acceleration? 30

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Answer Constant velocity means the object does not change its velocity over time Constant acceleration means that the object does not change its acceleration over time

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**REAL LIFE EXAMPLES OF CON A**

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**Almost all movement in life can be divided up into segments with constant acceleration**

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**Instantaneous acceleration**

Acceleration at a certain moment in time

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