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Key Concepts What kind of motion does acceleration refer to? How is acceleration calculated? What graphs can be used to analyze the motion of an accelerating object?. Acceleration. Key Terms. Acceleration . What is Acceleration?. Everyday language – the process of speeding up
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Key Concepts What kind of motion does acceleration refer to? How is acceleration calculated? What graphs can be used to analyze the motion of an accelerating object? Acceleration
Key Terms • Acceleration
What is Acceleration? • Everyday language – the process of speeding up • Scientific definition – the rate at which velocity changes • A change in velocity can be a change in speed or direction – or both • Therefore acceleration refers to increasing speed, decreasing speed or changing directions
Increasing Speed Examples: • A car moving from a stopped position • A car speeding up to pass another car • A person coasting down a hill on a bicycle
Decreasing SpeedNegative acceleration Examples • Softball landing in fielder’s mitt • A car stopping at a red light • Water skier when the boat stops pulling
Changing Direction Examples • A car following a bend in the road at constant speed • A car changing lanes on a highway • A softball as it changes directions when it is hit • Circular motion such as a Ferris wheel is continuous acceleration although the speed may not change
Calculating Acceleration • If an object is not changing direction you can calculate its acceleration as the rate at which its speed changes Formula: • Acceleration = Final speed – initial speed Time
Units for Acceleration If speed is measured in meters/second and time is measured in seconds, the SI unit for acceleration is m/s/s or m/s2 If speed is measured in km/hr and time is measured in hrs, the SI unit for acceleration is km/hr/hr or km/hr2
Acceleration Example • Look at the plane on p. 24 and 25 • The plane’s initial speed is 0m/s • The plane’s final speed is 40 m/s • The time it took for the plane to speed up to 40m/s was 5 s. • Acceleration = final speed – initial speed Time =40m/s-0m/s =40m/s =8m/s2 5s 5s
Graphing Acceleration • speed vs time graphs and distance vs time graphs can be used to analyze the motion of an accelerating object
Speed vs Time Graphs • Upward slanting line shows that speed is increasing • Downward slanting line shows that speed is decreasing • Straight line shows that acceleration is constant • Find acceleration by calculating the slope of the line – slope = Rise Run
Distance vs Time Graph • Represents the motion of an accelerating object • Curved line means an object is accelerating • Shows that during each second the object travels a further distance • Also shows that each second the speed is greater than the second before