Speed

1
Speed Following Distance

• Transportation Ch. 1, Act. 2

2
What do you think?

• What is a safe distance between your car and the
  car in front of you?
• Depending on your drivers education program
• 2 seconds
• 3 seconds
• 1 car length for every 10 mph
• How do you decide?

3
What is kinematics?

• Kinematics is the study of motion.
• Measurement of speed.
• Measurement of acceleration.

4
Speed

• How do we measure it?
• Speed (v) distance (d) / time (t)
• v d/t

5
Average vs. Instantaneous Speed?

• Average Speed Total distance traveled / total
  time.
• Average speed is independent of the path
  traveled.
• Average speed does not necessarily reflect your
  speed at a given moment in time.
• Instantaneous Speed The speed that you are
  traveling at at a specific moment in time.
• Speedometer reading.

6
Observing Speed

• Speed can be observed and represented in a couple
  of ways.
• Motion Diagrams A strobe representation through
  pictures of a moving object taken at a specific
  time interval.
• Graphs Speed can be determined through
  graphical analysis where the distance or velocity
  of an object may be measured vs. time.

7
Motion Diagrams
Stationary
Slow
Fast
Time
8
Graphical Analysis of Motion

• Distance vs. time When the motion is uniform,
  the slope of the line will give you the speed (v
  ?d/?t).

(t2, d2)
Slope (m) (d2 d1) (t2 t1)
(t1, d1)
9
Describe the Motion
Constant speed.
Constant speed followed by not moving.
10
Describe the Motion
Constant speed in the positive x-direction
followed by not moving, followed by moving at
constant speed in the negative direction.
Distance
Time
Constant speed in the positive x-direction
followed by a faster speed in the positive
x-direction.
Distance
Time
11
Describe the Motion
Uniform accelerated motion.
Distance
Time
12
Following distance

• What do you think is a safe following distance?
• Experts say that 2 seconds between vehicles is
  required to keep a safe distance from the vehicle
  in front of you. How many feet is this at
• 25 mph?
• 55 mph?
• 75 mph?
• Do these results surprise you?

73 feet
161 feet
220 feet