Tab 7 Speed Estimates. Skid Marks Sliding Objects Scuff Marks Linear Momentum Airborne Kinetic...
33
Tab 7 Speed Estimates
-
Upload
bethany-kelly -
Category
Documents
-
view
218 -
download
0
Transcript of Tab 7 Speed Estimates. Skid Marks Sliding Objects Scuff Marks Linear Momentum Airborne Kinetic...
Tab 7
Speed Estimates
Speed Estimates
Skid MarksSliding ObjectsScuff MarksLinear MomentumAirborneKinetic Energy
Energy of Motion
(Kinetic Energy)
= Energy to stop
(Work Energy)
½ M V2 Fd=
Determining Slide to Stop
Speed
Through algebraic substitution from one side of the equals sign to the
other, the above formula becomes:
FdMV 22
1
dfSmph 30
dfSkph 254
Three basic speed formulae
dfS 30
f
Sd
30
2
d
Sf
30
2
Three basic speed formulae
dfS 30
f
Sd
30
2
d
Sf
30
2
Speed from skid marks
Three basic speed formulae
dfS 30
f
Sd
30
2
d
Sf
30
2
Distance from speed and factor
Three basic speed formulae
dfS 30
f
Sd
30
2
d
Sf
30
2
Factor from speed and
distance (test skids)
Traffic Template 101
On a clean sheet of paper, draw a vertical
line from top to bottom in the middle of the
sheet
This page will be needed many times in the next couple days
Time for another test
Distance (feet)
Feet per Second
(Velocity)
Miles per Hour
(Speed)
Drag Factor or
Acceleration Factor
Acceleration Rate
(FPS2)
How many feet per second will a vehicle travel at 30 mph?
FPS = Speed (1.47)
FPS = 30 (1.47)
FPS = 44.1
Calculate using the Template
Metric: 1 Km/hr = 1000 meters in 3600 sec.
1000 m/3600 sec = 0.278 conversion factor
First, refer to
the “SPEED” side of
the center column
Second, using
the page you
made with the
line, place the
line horiz. across
the center column at 30 MPH
Third, on the FPS side of
the center
column, read the
cor-responding Feet per
Second opposite 30 MPH
30MPH = 44 FPS
If a vehicle travels 110 feet in one second, how many miles will it
travel in one hour?
Use your template to calculate the answer.
110 FPS = 75 MPH
What would be the safe following distance at 60 MPH, assuming a 2-
second following distance?
Use your template to calculate.
60 MPH = 88 FPS X 2 seconds
= 176 feet
A car left 100 feet of skid marks on a dry, traveled, asphalt surface. How fast was it going when it
began to brake?
Use your template to calculate.
First, decide what you’ll use
as the drag factor,
let’s say .70
Second, place your line
(horiz.) on the drag factor
column at .70
Third, place the other end of
the line on the 100-ft mark on
the distance (left) column
Fourth, read the SPEED in
the center column
~46 MPH
(Remember, MPH, not FPS)
A pickup skidded for 75 feet on a wet, traveled, asphalt road surface. How fast was it going when it began
to brake?
Use your template to calculate.
Drag factor = 0.60
Speed = ~36 MPH
How far will a car traveling 30 MPH slide to a stop on a surface with a
drag factor of .70?
Use your template to calculate.
Drag factor = 0.70
Speed = 30 MPH
Distance = 43 feet
How far will a car traveling 60 MPH slide to a stop on a surface with a
drag factor of .70? (If we double the speed, will the distance double,
too?)
Use your template to calculate.
Drag factor = 0.70
Speed = 60 MPH
Distance = 172 feet
If we double the speed, we quadruple the distance (so long as the factor remains
equal)
Similarly, if we double the speed, the Kinetic energy quadruples. This is due to the term “v2” in the formula KE = ½ Mv2
If you know two out of three, you can calculate the third:
If you know the factor and the speed, you can calculate the distance.
If you know the distance and the factor, you can calculate the speed.
If you know the distance and the speed, you can calculate the factor.
