23
012-05035E
Dynamics Cart Accessory Track Set
Experiment 7: Newton’s Second Law II
EQUIPMENT NEEDED:
– Dynamics Cart (ME-9430)
– Dynamics Cart Track
– Super Pulley with clamp
– Base and Support rod (ME-9355)
– String
– Mass hanger and mass set
– Stopwatch
– Wooden or metal stopping block
– Mass balance
(See Procedure Step
➂
)
Purpose
The purpose is to verify Newton’s Second Law,
F = ma
.
Theory
According to Newton’s Second Law,
F = ma
.
F
is the net force acting on the object of mass
m
and
a
is the resulting acceleration of the object.
For a cart of mass
m
1
on a horizontal track with a string attached over a pulley to a mass
m
2
(see Figure 7.1), the net force
F
on the entire system (cart and hanging mass) is the weight
of hanging mass,
F = m
2
g
, assuming that friction is negligible.
According to Newton’s Second Law, this net force should be equal to
ma
, where
m
is the
total mass that is being accelerated, which in this case is
m
1
+ m
2
. This experiment will
check to see if
m
1
g
is equal to
(m
1
+ m
2
)a
when friction is ignored.
To obtain the acceleration, the cart will be started from rest and the time (
t
) it takes for it to
travel a certain distance (
d
) will be measured. Then since
d
= (
1
⁄
2
)at
2
, the acceleration can
be calculated using
a
=
2
d
t
2
(assuming a = constant)
Procedure
➀
Level the track by setting the cart on the track to see which way it rolls. Adjust the leveling
feet to raise or lower the ends until the cart placed at rest on the track will not move.
➁
Use the balance to find the mass of the cart and record in Table 7.1.
➂
Attach the pulley to the end of the track as shown in Figure 7.1. Place the dynamics cart on
the track and attach a string to the hole in the end of the cart and tie a mass hanger on the
other end of the string. The string must
be just long enough so the cart hits the
stopping block before the mass hanger
reaches the floor.
➃
Pull the cart back until the mass hanger
reaches the pulley. Record this position
at the top of Table 7.1. This will be the
release position for all the trials. Make
a test run to determine how much mass
is required on the mass hanger so that
Figure 7.1 Equipment Setup
adjustable
end stop
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