MOTION

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## 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**• Distance: the length of a path between two points. • Considered a scalar quantity. (only a magnitude) • Can be expressed in any number of units. • Choose a unit that is best suited for the motion being described. • Examples: meters, kilometers, centimeters**Measuring displacement**• Displacement is independent of the path taken by the object. • Involves the starting point, ending point, anddirection.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 scalar**Average Speed**• Defined as the total distance / total time. Or • = d/t • Example problems on page 333**Instantaneous speed**• Not as useful in physical science. Much more difficult to calculate. • Defined as the speed at a given moment in time.**Graphing motion**• Distance-time graphs. • The slope of a line on a distance-time graph is the speed. • 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:**• 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/sec2**Example problems:**• 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 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/sec2**Graphing acceleration**• Distance-time graph for constant acceleration always a CURVE. • Velocity-time graph for constant acceleration always a STRAIGHT LINE.**Assignment:**• Pages 351-353 • 1-10, 17,18,19,20,21,24,29,30 • 1-5 page 353