Motion turn to 2.1 in your physics booklet January 22 nd 2009

Rate Rate - a change in some quantity divided by time For example: heart rate birth rate = babies per year speed = miles per hour

Speed Speed is the rate at which distance changes per unit time. speed = Δ distance / Δ time speed = Δd/Δt (Δ=change in)

Speed Average speed = total distance / total time v=Δd/Δt Instantaneous speed is the speed at a given instant (a small amount of time). Δt is close to zero

Velocity = speed with a direction. If either the speed or direction of a object changes, then its velocity changes. Velocity

Average speed, Instantaneous speed or Velocity?  Paul got pulled over for going 75mph.  A car is moving 30mph north on Hwy N.  He ran the mile in 5:33 minutes.

distance vs. displacement Displacement - length from the starting point to the ending point Distance - length of the path traveled ceDistance.html ceDistance.html

Acceleration Acceleration = rate at which your velocity changes per unit time a = Δv/Δt

Example Problem Calculate the acceleration of a car that goes from rest to 100 km/hr in 10 sec? a=? Δv= 100 km/hr Δt= 10 s a = Δv/Δt a = 100 km/hr / 10 s a = 10 km/hr/s

Example Problem A bike goes from 0-10 m/s in 5 second. What is its acceleration? a=? Δv= 10 m/s Δt= 5 s a = Δv/Δt a = 10 m/s / 5 s m/s/s=m/s 2 a = 2 m/s 2

Deceleration What is the acceleration of a pitch that slows from m/s in going from the mound to home plate in.41 seconds? m/s 2 Deceleration = negative acceleration

Free Fall  Ignore air resistance  Affected only by gravity  Gravity is symbolized by “g”  g=9.8 m/s 2  An object in free fall has a constant acceleration of 9.8 m/s 2 timeacceleration 1 s9.8 m/s 2 2 s9.8 m/s 2 3 s9.8 m/s 2

Free Fall  If you drop a ball off a cliff, how fast would it be going after 1 sec?  v=at timevelocity 0 s0 m/s 1 s9.8 m/s 2 s19.6 m/s 3 s29.4 m/s

Free Fall  If I drop an object, how far has it fallen after 1 sec?  Not 9.8 m  4.9 m  d=½at 2 resource/phy03.sci.phys.mfw.ga lileoplane/

Equations Velocity v=Δd/Δt or d=vt Acceleration a = Δv/Δt Free Fall (starting from rest) v=at d=½at 2

Review  Does the speedometer of a car read instantaneous or average speed?  What is the difference between speed and velocity?  What 3 controls on a car causes a change in velocity?  What is the acceleration of a car that travels at a constant speed of 100km/hr?

Distance vs. Time Graph  slope = velocity  neg. slope = change in direction  steeper slope= faster D i s t a n c e (m) Time (s)

Motion Graphs What does this graph represent?

Motion Graphs  What does this graph represent?

Motion Graphs

 What happens during this motion graph?

Motion Graphs Stage 1: 100 m in 10 s. Stage 2: 50 m in 10 s. Stage 3: 150 m in 20 s.

Motion Graphs  What does the exponential curve represent?

time distance Change in distance Change in time  d  t speed =  d /  t Slope = rise/run =  d/  t Is there an acceleration? Acceleration = v/t

Velocity vs. Time Graph  Slope = Acceleration  Neg. Slope = Deceleration  Neg. Velocity = change in direction  Steeper Slope = > Acceleration V e l o c i t y (m/s) Time (s)

Motion Graphs What can you tell me about this graph?

Motion Graphs  What can you tell me about this graph?

Motion Graphs  What can you tell me about this graph?

Motion Graphs  What about this one?

Motion Graphs  What is happening here?

..\Animations\motion graphs.avi

Examples Carl Lewis sprints from 0-11 m/s in about 4 seconds. What is his acceleration? 2.75 m/s 2 What is the acceleration of a downhill skier going from 0-70 m/s in 5 second? 14 m/s 2