Lab 03 cceleration
Purpose
Students will explore acceleration.
Theory
Acceleration happens any time the
speed changes. This is its definitionJtime-change in speed: a ? dv/dt. Zero
acceleration means the velocity is not
changing. Thus it is possible for speed
to be zero when acceleration is not (as
when a rocket first starts its engines)
and for acceleration to be zero when
speed is not (as when an elevator is in
steady motion).
An accelerometer is a device that
detects acceleration. Modern versions
use semiconductors in which electrical
transmission depends on the internal
stresses. Earlier varieties used simple
springs, but there is a far easier way.
Procedure
1. Procure a water bottle and a piece
of cord or string. Dental floss can be
used, as can a thread pulled from aging
cloth. It needs to be four inches or so.
2. Attach a small weight to the end of
the string. It can be a bit of twig or a ball
of aluminum foil, but it must float in
water when the time comes for that.
3. The label needs to be peeled off the
bottle because the weight will hang in
it and needs to be visible. The easiest
way to hang the weight in the bottle is
simply to screw the cap on, trapping
the thread against the rim.
4. Set the bottle upright on a tabletop
or a smooth floor and give it a minute
for the hanging weight to stop moving.
Now push the bottle suddenly to away
and observe the weight. It responds to
the accelerationn fact its horizontal
displacement is pretty much linearly
proportional to the acceleration, but
note the direction.
5. It should be possible to move the
bottle forward at a steady speed along
the floor or table (or just carry it) so
the weight doesn move appreciably.
Quickly stop it and observe the motion
of the weight. This event is a negative
acceleration`deceleration.
6. Fill the bottle with water with the
weight still in there. Screw the cap on
to trap the string again. Turn the bottle
upside-down do the weight floats in
the middle. Repeat steps 4 and 5.
Analysis
From the outside perspective, the
weight swings backward if the bottle
accelerates forward because the bottle
is trying to leave the weight behind.
From the viewpoint of the bottle, there
is an cceleration force,ike the one
seeming to push people back in their
seats when a car accelerates.
Please answer each of the following
in Canvas using complete sentences:
1. When the bottle moved at a steady
speed, what was its acceleration?
2. If the bottle is left to sit, the weight
grows still, but the surface of the earth
is going east at 1000 MPH. Why doesn
the accelerometer respond to this?
3. Suppose the bottle were hung from
the ceiling in a car and the car sped up.
The bottle would swing back in the car.
What would the weight do within the
bottle (no water, just air)? Why?
4. Did the weight do something weird
when the bottle was accelerated while
full of water? What did it do? Why?

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