Ithough mony foctors contribute to cor occidents,
speeding is the
most common kind of risky driving. Unsofe
speed is involved in
obout 2Oo/o of fotol cor occidents in the United
Stotes.
speed is the distonce on object trovers in
o certoin omount of time. For
exomple, o cor that trovels o distonce of g0
kilometers in one hour hos o
speed of 8o kilometers per hour. Any object,s
speed con be corculoted by
dividing the distonce troveled by the time token,
os shown in the equotion:
speed
--
distance
time
People use mony different units to describe
speed. These incrude miles per
hour (MPH), kilometers per hour (kph or tmih),
ond meters per second (m/s).
**_-*_*Fq
CHALLENCT
_F
How can you meosure the speed of o moving
cort?
This car speedometer shows
speed in miles per hour and
in kilometers per hour. Kilometers per hour is the speed
unit commonly used in other
cou
ntries.
E-7
Activity 74 . Measuring
Speed
r\4ATERIALS
a.
.=
la
For each group offour students
2
1
L
1
L
L
trqck pieces
cort
romp
timer
meterstick
morker
mosking tape
PROCEDUR.E
Pcrrt A: Measuring Time ond Distqnce
The fastest track qtclists
can travel a 4000 meter
(2.5 mile) trackin just
under 4 minutes.
E-8
1.
Set up the
2.
mosking tope, ond morker to meosure ond mork the
beginning ond end of the first 100 cm of the level port of the trock. Mok.
sure to ploce the tope next to the trock insteod of directly on the trock.
romp ond trock os shown below.
Use the meterstick,
Measuring Speed
.
Actvity
CarN eVeed
Trial
)ieLance (cm)
Time (e)
l
SVeed (cm/e)
rca
2
100
3
DA
Averaqe
3. In your science notebook,
moke o toble like the one
obove.
4.
Hold the cort so thot its
reor oxle is ot Notch A on
the romp.
5.
Releose the cort, ond stort
the stopwotch when the
reor wheels of the cort trov_
els over the beginning of
the level trock. Time how
Iong it tokes until the reor
wheels trovel to the 100 cm
mork. Record the time in
your toble in the Triol
1
row.
6. Repeot Steps
4-5 two more times.
your doto.
Use
the Triar zond 3 rows to record
the equotion berow to corculote the speed of the
cort for eoch triol:
distonce
speed
7. Use
=
time
8. Colculote the overoge of the three triors. Record
the overoge of the
speeds in your toble.
E-9
T4
Activity 74
"
Measuring Speed
Port B: The Effect of Relegse
Height
,rt
9. Imogine whot would happen to
the cort speed ifyou chonged
the releose height of the cort. In
your science notebook, write
how releosing it ot o lesser
height would offect its speed.
Exploin.
10. To test your prediction, write
o procedure thot uses the
equipment you hove olreody
experimented with.
f{int: Your plon should toke into occount thot the cort might not
olwoys trovel 100 cm before coming to o stop.
11. Prepore o doto table for recording
L2. Show
13.
your meosurements.
your plons to your teocher.
Corry out your experiment qnd record your doto.
ANA
I-YS IS
{l*
L.
{l' *
2' According to your doto from Port B, whot is the effect of releose height
on speed?
)a
d.:
ffi
.&::
e
t".l!,,kt
d;*
According to your doto from Port A, whot is the speed of the cort?
List some common units for speed. Why ore there so mony different
units?
4. Whot port(s) of your experimentol design
o.
b.
increosed your confidence in the results?
decreosed your confidence in the results?
5. Whot is o cor's speed
o.
b.
in Port B:
5 meters
in m/s if it trovels:
in 0.L seconds?
5 meters inO.2 seconds?
c. L0 meters inO.2 seconds?
6.
Reflection: Why
do you
fotol cor occidents?
E-'t0
think speeding is o foctor in obout
2Oo/o
of
Measging Speed A*ivity 74
ffiXTENSION '!
.
Wsical Science poge of the SEPUP
website, ond compore your doto set to thqt of students in other closses.
Post your results on the /ssues and
HXTENSION
2
*
If the speed Iimit is 60 MPH, could the police give o speeding ticket to ony
of the drivers of the cors in Anolysis Question 5?
Hint:
1,000 m = 1 km = 0.62 miles
i*
to medsure how far a car moves in a short amount of time. lt quickly
calculates the speed dnd displays it for the user.
A radar gun
uses sound wdves
E-11