PASCO ME-9481 Bernoulli Cart Accessory - Manual

Instruction Sheet
for the PASCO
Model ME-9481
Bernoulli Cart Accessory
012-05214A
3/93
$1.00
Bernoulli Cart
Accessory
String (approx. 1m)
Screws
Lower Air
Speed –
Higher
Pressure
Fan
Introduction
The PASCO ME-9481 Bernoulli Cart Accessory at-
taches to the PASCO Dynamics Cart (ME-9430) or
Collision Cart (ME-9454) to demonstrate Bernoulli’s
Principle. The cart should be used on a PASCO Dynam-
ics Track to minimize friction. A fan (approximately 6-
inch to 12-inch diameter) is required to supply moving
air.
The Bernoulli Cart Accessory consists of a vertical
cylinder that can be rotated rapidly by pulling on a
string. (➤ NOTE: String for spinning the cylinder and
two screws for mounting the apparatus on a PASCO cart
are included.) When the fan blows air perpendicularly
across the track, the cart moves along the track in a
direction corresponding to the direction of rotation of the
cylinder.
Theory
According to Bernoulli’s Principle, the pressure in an
incompressible moving fluid is lowest where the speed
of the fluid is highest.
Figure 1 shows the top view of the cylinder mounted on
the cart with the cart sitting on the track. The fan is
AIR
DRAG
AIR
DRAG
+ =
FAN FAN
DIRECTION OF MOTION
+ =
blowing air by the cylinder, perpendicularly across the
track. If the cylinder was not rotating, the air-speed
passing by the front and back of the cylinder would be
the same. The pressure in the front and back would be
equal and the cart would not move.
Figure 1A: Top View of Rotating Cylinder
Figure 1B: Air Distribution
When the cylinder is spinning clockwise (
ω
down) as
shown in Figure 1, friction between the cylinder walls
and the air causes the speed of the air in front of the cart
to become greater than the speed of the air in back of the
cart.
According to Bernoulli’s Principle, the faster moving air
in front of the cart exerts less pressure on the cylinder
than the slower moving air in back of the cart. This
difference in pressure produces a net force which causes
the cart to move forward along the track. If the cylinder
is spun in the opposite direction (counterclockwise,
ω
up), the pressure is less in back of the cart and the cart
moves backward.
Front of
Cart
Cart
moves in
this
direction
Track
Higher Air
Speed –
Lower
Pressure