Ch 11 Motion

Motion  A change in position  How do you know something has moved?

 Frame of reference (reference point) = system of objects that are not moving with respect to one another  Relative Motion = movement in relation (or relative)to a frame of reference  Relative Motion = movement in relation (or relative) to a frame of reference

Distance versus Displacement  Distance is the length of a path between two points  SI Unit is meter (m)

 Displacement is the length from the starting point to the ending point

Examples: What is the total displacement? 4m + 2m + 4m + 2m = 12m What is the total distance traveled? ZERO

How is the speed limit measured?  Miles per hour  What 2 things are considered? –Distance (miles) –Time (hour)

Speed  the ratio of the distance (d) an object moves to the amount of time (t) the object moves  SI Unit is meter per second (m/s)  V=d/t, d=Vt, t=d/V Distance Velocity time

Speed  Average speed = computed for the entire duration of the trip  Instantaneous speed = measured at a particular instant

 Florence Griffith Joyner set a world record by running 200m in 21.34s. What was her average speed?  9.37 m/s  Sound travels at a speed of 330m/s. If a lightning bolt strikes the ground 1000m away from you, how long will it take for the sound to reach you?  3.03 s

 Velocity (V) = the speed & direction an object is moving  Vector = a quantity that has magnitude & direction

Same speed & direction = velocity

Distance-Time graph  Slope tells me SPEED!  Horizontal part tells me the object stopped moving=no motion=no velocity  Straight portions tell me constant speed  Greater the slope the higher the speed, vice versa

Graphing speed

Distance-Time Graphs

No motion=stopped

STAR cards  What is a reference point?  An objects that is not moving  What are the units for speed?  Meters per second  What does the horizontal line on a Distance-Time graph mean?  That the object is not in motion, it’s still

Acceleration  Is the rate at which velocity changes  changes in speed  changes in direction  changes in speed & direction  SI unit is meter per second per second (m/s 2 )

Acceleration  The triangle is the Greek symbol delta, means “change in”  Vf = final velocity  Vi = initial velocity  Vf-Vi (final minus initial)

Δ VΔ V at V f – V i SI unit is meter per second per second (m/s 2 )  Why are the seconds squared?

Which car has greatest acceleration? The blue car undergoes the greatest acceleration bc its velocity is changing at a more drastic rate The red car is actually not accelerating at all. It has a constant velocity the entire race.

Distance-Time graph for the cars, Which car goes with which line? Red=B Blue=A Green=C

Distance-Time Graph Curved parts tells me object is increasing & decreasing speed = changing velocity over a time period = acceleration

Speed-Time graph  Slope tells me acceleration!  Horizontal part tells me object is at constant speed (velocity) = no acceleration  Slope downward tells me object is slowing down (decelerating or negative accleration)

Graphing constant acceleration

Speed-Time Graph Constant speed/velocity STOPPED!

 The speed limit changes from 55m/s to 0m/s. To make the change in 10s, what acceleration will it require?

 A car’s acceleration is 3m/s 2. if the car started at rest and it only took 10s for the car to reach this acceleration, what is the car’s final velocity?

 A=9.8m/s 2  Vf=0.5m/s  Vi=?  t=3s

STAR cards  What is a vector?  a quantity that has magnitude & direction  What is acceleration?  Is the rate at which velocity changes  What does horizontal part on a speed-time graph tell me?  object is at constant speed (velocity) = no acceleration  What does horizontal part of a distance-time graph tell me?  No speed, no motion, object is stopped  What does curved part on a distance-time graph tell me?  Acceleration