Data Sheet

-108-
242. Sound from Motor
Build the circuit shown on the left, press the switch (62) and you will
hear a faint siren from the motor (95). The motor (95) is actually acting
as a speaker. As discussed in project #41, current through the motor
(95) creates a force on the shaft. It turns out this force is also being
applied to the shell of the motor (95) and the shell of the motor (95) is
acting like a cone in a speaker, which is creating the sound you hear.
243. Speed of an AC Motor
Place a 4-wire (4) across points C and D and when you press the switch
(62) you will hear a faint gun shot and machine gun sounds. The number
of poles in an AC motor, combined with the AC line frequency, can be
used to determine the non-load speed of a motor. The derivation of the
formula is beyond the scope of this manual but the result is that the
speed of an AC motor is equal to 120*f
l
/p where f
l
is the line frequency
of the AC power source and p is the number of poles in the motor. In the
United States the AC line frequency is 60 Hz, and thus a simple 2-pole
AC motor would spin at a rate of 120*60/2 = 3,600 RPM.
244. Motors in a Car
Place a 4-wire (4) across points A and B and when you press the switch
(62) you will hear the faint sound of an emergency re siren. Cars are a
major consumer of motors. Did you know that an average car contains
around 30 motors? See how many motors you can count in your car.
245. Engine vs. Motor
Place a 4-wire (4) across points E and F and when you press the switch
(62) you will hear faint space battle sounds. Hopefully you did not
count the engine in your car as a motor in project #244. They are two
different things. Motors run on electricity (from the batteries in these
projects), while engines run on combustion.
246. Combustion for Car Engines
Place a 4-wire (4) across points G and H and when you press the
switch (62) you will hear music. Combustion in car engines is the
process where fuel (e.g. the gas you put in your car) is ignited in a
small, enclosed space to create energy that is used to create a force
that ultimately provides motion to your car.
WARNING: Moving parts. Do not
touch the motor during operation. Do
not lean over the motor.
!
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