 # MOTION Chapter 11 How do you know something is moving?  Depends on your frame of reference.  A frame of reference is the location from which motion.

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MOTION Chapter 11

How do you know something is moving?  Depends on your frame of reference.  A frame of reference is the location from which motion is observed.  Most common: the earth.

Measuring distance DDistance: the length of a path between two points. CConsidered a scalar quantity. (only a magnitude) CCan be expressed in any number of units. CChoose a unit that is best suited for the motion being described. EExamples: meters, kilometers, centimeters

Measuring displacement  Displacement is independent of the path taken by the object.  Involves the starting point, ending point, and direction. Vector quantity  Example:

Adding vectors  When the vectors are along the same plane they are added arithmetically.  Many different methods for adding vectors that do not lie in the same plane.  Examples on board

What is SPEED ?  The ratio of distance an object moves to the amount of time it takes to move that distance.  How fast or slow an object is traveling.  Is speed a vector or a scalar quantity

Average Speed DDefined as the total distance / total time. Or  = d/t EExample problems on page 333

Instantaneous speed NNot as useful in physical science. Much more difficult to calculate. DDefined as the speed at a given moment in time.

Graphing motion DDistance-time graphs. TThe slope of a line on a distance-time graph is the speed. AAt what speed is the student walking down the hallway?

Speed vs velocity  Velocity is speed in a given direction.  MUST have a direction.  Considered a vector quantity

What is acceleration?  A situation in which the velocity is changing.  “Speeding up or slowing down”  “changing direction”  Science definition: the rate of change of velocity  Can be both negative and positive  Acceleration is a VECTOR quantity.

Acceleration examples: WWhich car is experiencing acceleration?

If you said the red and blue car you were right!  A distance-time graph of all three cars:  The distance-time graph for accel. Is always a curve.

What is the formula for acceleration?  Acceleration = final velocity – original velocity time Or the change in velocity ( ( v) / change in time (  t)  Label : m/sec/sec or m/sec 2

Example problems: AA roller coaster’s velocity at the top of a hill is 10 m/sec. Two seconds later it reaches the bottom of the hill with a velocity of 26 m/sec. What is the acceleration of the roller coaster?

More examples:  A roller coaster is moving 25 m/sec at the bottom of a hill. Three seconds later it reaches the top of the hill and is traveling at a speed of 10 m/sec. What was the roller coaster’s acceleration?  Can you have negative acceleration?  YES. The negative sign tells us the direction of the acceleration, usually means deceleration.

Free Fall  Acceleration due solely to the force of gravity.  All objects fall at the same rate.  9.8 m/sec 2

Graphing acceleration  Distance-time graph for constant acceleration always a CURVE.  Velocity-time graph for constant acceleration always a STRAIGHT LINE.

Example graphs:

Assignment:  Pages 351-353  1-10, 17,18,19,20,21,24,29,30  1-5 page 353

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