PASCO ME-9502, Руководство пользователя, Страница: 17 / 94

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M o d e l N o . M E - 9 5 0 2 E x p . 2 : A d d i n g F o r c e s — R e s u l t a n t s a n d E q u i l i b r i a n t s
0 1 2 - 1 2 8 7 6 B 13
Exp. 2: Adding Forces—Resultants and Equilibriants
Equipment Needed
Theory
In figure 2.1, Person A and Person B are pulling with forces represented by F
A
and
F
B
on a car stuck in the mud. Since these forces are acting on the same point of the
car, they are called concurrent forces. Each force is defined both by is direction
(the direction of the vector arrow), and by its magnitude, which is proportional to
the length of the vector arrow. (The magnitude of the force is independent of the
length of the tow rope.)
The total force applied by the two people can be determined by adding vectors F
A
and F
B
. The parallelogram method is used in the example. The diagonal of the par-
allelogram is called the resultant , F
R
. It shows the magnitude and direction of the
combination of F
A
and F
B
.
Because the car is not moving, the net force on the car must be zero. The friction
between the car and the mud is equivalent to the resultant force,
F
R
. This equivalent
opposing force is called the equilibriant , F
E
. This force has the same magnitude as
the resultant, F
R
, and it has the opposite direction of the resultant.
Setup
Set up the Spring Scale and Force Wheel on the Statics Board as shown. Twist the
Force Wheel until the bubble level shows that the Force Wheel is level. Attach one
of the threads from the force disk (inner part of the String Tie) in the center of the
Force Wheel to the bottom hook of the Spring Scale. Connect a second thread to a
mass hanger (let the third thread dangle). Add 80 g (0.080 kg) to the mass hanger.
Adjust the Spring Scale up or down so that the force disk is centered in the Force
Wheel. The mass hanger applies a force downward,
F
g
= m g (the force due to grav-
ity, where m is the total mass of the mass hanger). When the force disk is centered,
the system is in equilibrium, so the downward force
F
g
must be balanced by an
equal and opposite force, the equilibriant , F
E
. In this case, the equilibriant force,
F
E
, is applied by the Spring Scale.
Item Item
Statics Board Mounted Spring Scale
Force Wheel Large and Small Pulleys
Mass and Hanger Set Thread
Figure 2.2: Setup
Force
Wheel
Bubble
level
Force
disk
Spring
Scale
Thread
Force
disk
F
g
= mg
F
E
= mg
Figure 2.1: Resultant and Equilibriant
F
A
F
B
F
R
F
E
Car