2.1 to 2.3

Displacement, Velocity, and Acceleration

2.1 Displacement

• Mechanics

– Kinematics• Describes motion

– Dynamics• Describes effects of forces on motion

Displacement

• Change in position

• x0 = initial position

• x = current position

x = displacement

Displacement

x = x – x0

• Meter

• In 1-D– Right is positive– Left is negative

Displacement vs. Distance

• Displacement = final pos – initial pos

• Distance = total distance traveled

Speed vs. Velocity

• No Direction

• m/stime

distanceSpeedAve

Time

ntDisplacemeVelocity Ave

• Direction • m/s

Average Velocity

• The football player ran 50 m in 20 s. What is his average velocity?

• v = 50 m / 20 s = 2.5 m/s

0

0vVelocity Avett

xx

t

x

Your turn

• The little kid ran 35 m, then turned and ran 15 m back. If he started running at 1:05:00 and ended at 1:06:10, what was his average speed?

• Average velocity?

Instantaneous Velocity

• How fast going at this instant

• As t small, – Average velocity instantaneous velocity

t

xv

t

lim0

2.3 Acceleration

• Describes changes in velocity

• + faster

• - slower

• 0 constant velocity

• Units: m/s2

Ave a vs. instant a

0

0att

vv

t

v

t

va

t

0

lim

Acceleration

• A car goes from 0 to 100 m/s in 6 s. What is its average acceleration?

• a = 100 m/s / 6 s = 16.7 m/s2

v = 100 m/s

a = 16.7 m/s2

Your turn

• A racecar traveling at 320 km/h hits a barrier and stops in 2 s. What was the average acceleration? (Don’t forget to convert to m/s!)

• a = -44.5 m/s2

v = 88.9 m/s

a = -44.5 m/s2

Practice Work

• You can complete

• 48 #CQ1 – 5, P1 – 5, 7 – 9, 12 – 15

• Total of 17 problems