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Physics Unit 2 1-D and 2-D Motion

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Topics: 4 What is Linear Motion? 4 Vector vs. Scalar Quantities 4 Distance vs. Displacement (Comparison) 4 Speed vs. Velocity (Comparison) 4 Velocity: Constant, Average, Instantaneous 4 Acceleration

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Linear Motion 4 Motion in one direction 4 Example: the motion of a Marta train- the train moves either forward or backward along the track

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SCALAR PHYSICAL QUANTITY Can be completely specified by its magnitude with appropriate units. It has no direction. Ex) Distance, time, speed, mass, etc.

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PHYSICAL QUANTITY VECTOR Has a magnitude, a unit and a direction e.g displacement, velocity, acceleration, force.

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Demonstrating a Vector The direction of the arrow indicates the direction of the vector quantity. The length of the arrow indicates the magnitude of the vector quantity. A Tail Head

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ADDING VECTORS -ONE DIMENSIONAL 4 Vectors are added by placing the tail of one vector at the head of the other vector. 4 A third vector (C) is drawn by placing the tail of one vector at the head of the other. AB C

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EXAMPLES 200m100 m 300 m-resultant 50 m 30 m 20 m-resultant

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Distance How far an object actually moves

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Displacement Displacement does not always equal distance traveled Displacement can be positive or negative

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Displacement

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Displacement is ZERO

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Distance vs. Displacement 4 Displacement- a change in position d = d f - d i final position - initial position

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Displacement Questions 1. Amy runs 2 blocks south, then turns around and runs 3 miles north. 2. Jermaine runs exactly 2 laps around a 400 meter track. 3. Ray runs 30 feet north, 30 feet west, and then 30 feet south. 4. Jamison turns around 5 times. 5. David walks 3 km north, then turns and walks 4 km east.

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Speed and Velocity

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Speed 4 Speed is a rate 4 Speed is a rate of the distance traveled in a unit of time

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Speed 4 Speed is a measure of how fast something is moving 4 Speed is a SCALAR quantity- it only requires a magnitude

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Calculating Speed Speed = Distance traveled Time

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What is the fastest land animal? 4 The cheetah can travel at speeds up to 100 km/h!!

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Velocity 4 The terms speed and velocity are used interchangeably 4 Velocity is speed in a given direction

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Velocity 4 VECTOR quantity- it must have both magnitude and direction –magnitude is a number –direction: north, south, east, west, etc.

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Units of Speed and Velocity 4 Units of distance /unit of time 4 Meters/sec, miles/hour, kilometers/hour, nanometers/sec,

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Velocity Graphs (position vs. time) A B A C B D

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Constant velocity 4 Occurs when the average velocity is the same for all time intervals 4 Also called uniform velocity

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Constant Velocity Graph 4 The velocity is equal to the slope of a distance versus time graph

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Average Velocity 4 Used to describe an objects motion when the velocity is changing, i.e. speed up, slow down, stop, start, etc. 4 Average velocity will equal the magnitude of an object moving with a constant velocity.

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Calculating Average Velocity 4 Total distance (displacement)/total time 4 slope of line drawn from start to stopping point on a distance time graph.

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Average Velocity 4 DISPLACEMENT divided by TIME v avg = average velocity = change in position = displacement change in time time interval

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Instantaneous Velocity 4 The velocity of an object AT a particular INSTANCE or moment.

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Instantaneous Velocity 4 Determined by drawing a tangent line to the curve and determining the slope of the line.

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Example 4 During her first track meet, Andrea runs with an average velocity of 6.02 m/s to the east. What distance does Andrea cover in 137 s? Given: v = 6.02 m/s t = 137 s d = ? V=

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Example 4 Last weekend I traveled from Lawrenceville to Dillard (100 km). If I drove 50 km/h for the first 50 km and 100 km/h for the second 50 km, what was my average velocity?

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Acceleration Acceleration is the rate of change in velocity

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Acceleration Acceleration is shown by a curved graph when position (distance) versus time is plotted.

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