Transcript Velocity and Acceleration

 Reference
point- stationary object that helps
you determine how far something moved
 Distance- how far an object moves
• Unit- meter (m)
 Displacement-
distance and direction of an
object’s change in position from the starting
point
 Speed – distance traveled per unit time
• s = d/t
• Speed = distance / time
• Unit- m/s
 Average
speed- total distance divided by
total time
 Instantaneous
speed- speed at that
moment
• Like your speedometer
 Constant
speed- speed doesn’t change
 Distance-time graph- has time on the xaxis and distance on the y-axis
• Slope is speed
• Steeper line = faster
• Flat line = stopped
• Negative slope = moving backwards
Speed of Swimmers
700
Distance (m)
600
500
Adam
400
Jeff
300
Cory
200
100
0
0
5
10
Time (min)
15
20
25
 If
you know that a hurricane is moving at 20
km/h, and it is 100 km away from you, do
you need to be concerned?
• Maybe- you can’t tell- it might be headed toward you
or away from you!!
 Velocity
– Speed and direction
 Car one is headed east at 50 mph. Car two
is headed west at 50 mph. Do they have the
same speed? The same velocity?
• Speed – yes
• Velocity - no
 Are
you moving if you are sitting 100% still
in your chair??
• YES! The earth is moving and you are on the earth,
so you are moving relative to the other planets, the
sun, etc.
• NO! Relative to the floor, you are not moving
• It all depends on your frame of reference
 Relative
motion – motion depends on your
frame of reference
• http://www.phy.ntnu.edu.tw/ntnujava/index.php?top
ic=140
 Acceleration- rate of change in velocity
• Occurs when speed or direction changes
• Negative acceleration- when something slows
•
•
•
•
•
down
Positive acceleration- when something speeds
up
Change in velocity / change in time =
acceleration
Acceleration = Force / mass
Units m/s2
Acceleration due to gravity = 9.8 m/s2
Aircraft acceleration
700
Speed (m/s)
600
500
Airplane 1
400
Airplane 2
300
Airplane 3
200
100
0
0
5
10
Time (sec)
15
20
25
 Slope
= acceleration
• Flat slope = constant speed
• Positive slope = sleeping up
• Negative slope = slowing down
 Choose
one option:
• You have 2 toy cars. Which one will have the
greatest velocity with the same force applied to
both?
• You have 2 toy cars. Which one will have the
greatest acceleration with the same force
applied to both?
 Or do both for extra credit!