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Acceleration

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**Acceleration Acceleration = speeding up**

Acceleration – the rate at which velocity changes Can be an: Increase in speed Decrease in speed Change in direction

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**Types of acceleration Increasing speed Decreasing speed**

Example: Car speeds up at green light Decreasing speed Example: Car slows down at stop light Changing Direction Example: Car takes turn (can be at constant speed) screeeeech

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Question How can a car be accelerating if its speed is a constant 65 km/h? If it is changing directions it is accelerating

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**Calculating Acceleration**

If an object is moving in a straight line Units of acceleration: Distance/ time = distance/time2 time m/s2

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**Calculating Acceleration**

0 s 1 s 2 s 3 s 4 s 0 m/s 4 m/s 8 m/s 12 m/s 16 m/s

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Question A skydiver accelerates from 20 m/s to 40 m/s in 2 seconds. What is the skydiver’s average acceleration?

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**Graphing Acceleration**

Can use 2 kinds of graphs Speed vs. time Position vs. time

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**Graphing Acceleration: Speed vs. Time Graphs**

Speed is increasing with time = accelerating Line is straight = acceleration is constant

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**Graphing Acceleration: Speed vs. Time Graphs**

Rise = 4 m/s Run = 2 s In Speed vs. Time graphs: Acceleration = Rise/Run = 4 m/s ÷ 2 s = 2 m/s2

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**Graphing Acceleration: Position vs. Time Graphs**

On Position vs. Time graphs a curved line means the object is accelerating. Curved line also means your speed is increasing. Remember slope = speed.

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**Question Run = 3 s Rise = -6 m/s**

Above is a graph showing the speed of a car over time. 1) How is the speed of the car changing (speeding up, Slowing down, or staying the same)? 2) What is this car’s acceleration? The car is slowing down Acceleration = rise/run = -6m/s ÷3s = -2 m/s2

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**curved line = accelerating, straight line = constant speed**

Question: The black and red lines represent a objects that are accelerating. Black is going a greater distance each second, so it must be speeding up. Red is going less each second, so must be slowing down Remember: in position vs. time graphs: curved line = accelerating, straight line = constant speed Which line represents an object that is accelerating?

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Question: Hard one

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Free fall The constant acceleration of an object moving only under the force of gravity If there was no air, all objects would fall at the same speed regardless of the masses

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**Acceleration due to gravitational force**

d = vit + ½gt2 If vi = 0, then d = ½ gt2 g = acceleration due to the force of gravity = 9.8 m/s2 = 10 m/s2

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**Free fall After 1 second falling: v= 10 m/s**

After 2 seconds: v = 20 m/s After 3 seconds: v = 30 m/s

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**Falling Air resistance will increase as it falls faster**

An upward force on the object Eventually gravity will balance with air resistance Reaches terminal velocity - highest speed reached by a falling object.

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Bozeman videos

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Questions Answer the following questions and me your answers. ) 1. How can a car accelerate without the speedometer changing? 2. What does the slope of a velocity vs time graph give you? 3. What is the value of the acceleration due to the force of gravity on Earth? 4. What is the color of the object that is rolled across the table by Mr. Andersen?

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Acceleration- Change in Velocity

Acceleration- Change in Velocity

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