Download Potoourii of Interia Demos - Otterbein Neutrino Research Group

Interia Demo’s
1. Mass on a rod/Balancing Stick
2. Water on a Tray
3. Mass on a String
4. Eggs Over Easy
5. Coins on a Coat Hanger
6. Toilet Paper Jerk
7. Ken & Barbie
8. Chalk on a Hoop
9. Apple Slices
10. Croquet Balls on Head
11. Tablecloth
12. Egg Spin
13. Bike Tire
14. Roto-rider
15. Inertia Video
1. Mass on a rod/Balancing Stick
http://www.exploratorium.edu/snacks/balancing_stick/index.html
The dowel rotates more slowly when the mass is at the top, allowing you
more time to adjust and maintain balance. When the mass is at the bottom,
the stick has less rotational inertia and tips more quickly. The farther away
the mass is located from the axis of rotation (such as in your hand), the
greater the rotational inertia and the slower the stick turns. An object with
a large mass is said to have a great deal of inertia. Just as it is hard to
change the motion of an object that has a large inertia, it is hard to change
the rotational motion of an object with a large rotational inertia.
You can feel the change in inertia when you do the following experiment.
Grab the end of the dowel that's near the clay. Hold the dowel vertically,
and rapidly move the dowel back and forth with the same motion you would
use to cast a fishing line. Next, turn the dowel upside down, and hold it at
the end that is farthest from the clay. Repeat the casting motion. Notice
that it is much harder to move the dowel rapidly when the clay is near the
top. The mass of the stick has not changed, but the distribution of the mass
of the stick with respect to your hand has changed. The rotational inertia
depends on the distribution of the mass of the stick.
2. Water on a Tray
http://www.stevespanglerscience.com/experiment/00000145
This demo is a slight modification of the classic swinging pail of water demo. The picture
shows the construction of the "spinning platform." The base is made from a square piece
of Plexiglass measuring approximately 12 inches. Drill holes in all four corners large
enough to accommodate a piece of rope. Attach the ropes to each corner of the platform
and join them together in a knot about 2 feet above the platform.
Now that all of the difficult work is finished, it's time to swing the tray and plastic cup
(several plastic cups if you're feeling lucky) around in a complete circle without spilling
the liquid or flinging the cup around the room. It's the tendency for the plastic cup and its
contents to go in a straight line that allows it to seemingly defy gravity. The centripetal
force provided by the tension in the cords is large enough to create enough friction to
hold the plastic cup(s) in place.
Here's a little advice... practice swinging the tray around without the cups in order to get
the feel of a smooth, circular motion. Then add the cup filled half full with water. The
liquid adds mass to the cup and helps to keep the cups in place. Some demonstrators even
glue a thin piece of rubber to the bottom of the cup to give it a little gripping power
(okay, friction) to help the cups stay in place. Shhhh! That's a little secret between you
and me.
How does it work?
Here's the heavy-duty science for people who really care...
According to Newton's First Law of Motion, objects in motion tend to remain in motion
unless acted upon by an external force. In this case, Newton's Law requires the water to
continue moving along a tangent to the circle. Thus a force is required to keep it always
turning toward the center of the circle. The interpretation of this demonstration is
potentially confusing when one considers that at the top of its arc, the water is
accelerating downward because of the motion, but that the force of gravity is also
downward. One can explain that F = ma is thus satisfied without the water leaving the
bucket. This demonstration provides the opportunity to discuss non-inertial (accelerated)
frames of reference and inertial (fictitious) forces (such as the centrifugal force
3. Mass on a String
http://sirius.ucsc.edu/demoweb/cgi-bin/?mechan-statics-inertia
Two equal weights suspended by threads, while two more threads hang below them with
short rods for handles. When the handle is pulled down with a jerk, the lower thread
breaks, but when it's pulled with an even force, the upper thread breaks.
4. Eggs Over Easy
http://www.stevespanglerscience.com/experiment/egg-drop-inertia-trick
We did it with a bent meter stick
Materials:
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Small ball to practice with, if desired
Cardboard tube
Pie pan
Raw eggs
Water
A large drinking glass
Oh, you might need a few paper towels to clean up your practice mess!
5. Coins on a Coat Hanger
http://www.wonderhowto.com/how-to-perform-easy-magic-trick-with-coathanger-and-coin-412841/
Same idea as the trick we showed but better
This magic trick is really not so much a feat of illusion as a dizzying demonstration of physics.
This video will show you how to do this easy trick with only a humble coin and coat hanger as
props that will dazzle your audience for about 20 seconds with practice.
6. Toilet Paper Jerk
Two rolls of toilet paper, one full and the other almost gone, are placed on a rod so that
they are free to rotate. Inertia is discussed. Inertia is a measure of how difficult it is to get
something to move. We use weight and mass to measure inertia. The heavier something
is, the more inertia it has, and the harder it is to get it to move. A very sharp or fast blow
applied to something with a lot of inertia is more likely to break it rather than move it.
The same blow applied to something with less inertia is more likely to move it. It is very
easy to rip off one or two squares of toilet paper with a quick jerk of one hand from a full
roll without having it spin and unravel because of it's large inertia. However, it is almost
impossible to do this with a roll that is almost gone. Because of it's low inertia, it is much
easier to move.
7. Ken & Barbie
Objective: to demonstrate Newton’s First Law of Motion (Inertia) students can see
that objects at rest will stay at rest. Objects in motion will remain in motion unless a
force is acting upon it. The motion of objects will continue in a straight line. Objects
will eventually stop due to friction. This demonstration also covers Newton’s Second
Law of Motion – Forces and Acceleration. When the “unbuckled” doll is launched, it
accelerates – force causes acceleration. The force acting upon the “dolls” in the
accident is the object the doll hits.
Materials: 2 dolls
1 doll secured; 1 doll unsecured (duct tape)
1 skateboard
Block/barrier to stop the board and eject one of the dolls
Procedure:
1. Place the dolls on skateboard; secure one by taping or tying down.
2. Use a decline ramp (simply release the board) and place a barrier at the end of the
route or push board on a level plane.
3. One doll should be launched to demonstrate acceleration and a net force acting on
the “vehicle.”
Conclusion:
Two laws are observed. The board is in motion until acted upon by a net force. The
dolls are at rest while on the board and Barbie stays at rest because she is buckled and
Ken accelerates when acted upon by a net force (the barrier the board hits) and is
propelled into the air. Ken accelerates while Barbie does not. To accelerate the mass
it has to have a net force applied to it; the less mass the easier it is to accelerate. For
example, a shopping cart full of groceries and a cart with just a gallon of milk. The
lighter cart will accelerate at a faster rate than the other shopping cart.
Science Terms:
Inertia – An object at rest will remain at rest, an object in motion will remain in
motion unless acted upon by a net force
Friction – A resistance by having contact of solid to solid OR solid to air/water;
eventually slowing an object down. Friction has three types on a surface: sliding,
rolling, and static
Acceleration – The rte in which velocity (speed together with the direction of the
motion) is changing
Net force – The combination of all forces acting on an object. For example: if you
pull on an object at rest with 10 N (Newton) on a frictionless surface, then the net
force will be 10 N and it is being acted upon by a “net force” of 10 N as it moves.
Enrichment:
A motorcycle accelerates from rest to 31 m/s in 10 seconds. Find the motorcycle’s
average acceleration. Solve for acceleration:
a = 31 m/s – 0 m/s
10 s
8. Chalk on a Hoop
A piece of chalk is at rest on a very flexible hoop that has been balanced on top of
a narrow neck bottle. When one tries to remove the hoop with a quick strike in the
horizontal direction, the flexible hoop will change its shape to an oval one. As a
result of the very low friction between the chalk and the hoop, the piece of chalk
will fall straight into the bottle
9. Apple Slices
Puncture a knife through an apple. Hold the knife so it is pointing down
with the apple at the tip of the knife. Pound your fist on to the knife
handle and the apple will appear to move up the knife. It is really a
demonstration of inertia. The apple is at rest and wants to remain at
rest. The knife moves downward
Start
Finish
10. Croquet Balls on Head /Mr. Potato Head
Objective: This demonstration shows Newton’s First Law of Inertia. Objects at rest
will stay at rest unless acted upon by a net force. The demonstration focuses on the
object staying at rest, although there is a quick movement that occurs (turning your
body). The interruption is brief, similar to a table cloth being yanked and the dishes
remain.
Materials:
1 coat hanger
2 potatoes or clay balls placed at each end
Procedures:
Prior to the demonstration, have students predict what will happen if you decide to
“turn around” and face the other potato behind your head. Create camps of opinion
and see which group’s prediction was correct. To create a potato head, open the
hanger so it’s straight and then bend into a V-shape. Place the potato at each end; the
weighted hanger will balance on your head. Have a potato in front of your face, and
then quickly turn yourself around so that you will be facing the other potato.
Conclusion:
Students will see that the potatoes stayed at rest even though you were in motion.
Friction is a factor that keeps or slows the hanger from moving. Newton’s first laws is
observed when the potatoes stay at rest and you are in motion. Have students create or
think of other ways to demonstrate this phenomenon.
Science Terms:
Inertia – An object will remain at rest OR an object in motion will remain in motion
and move at a constant speed unless a force is applied
Friction – A force that resists sliding between two touching surfaces or through air or
water. Friction slows down an object. There are three types: static, sliding, and rolling
Enrichment:
Have students create or think of other ways to demonstrate this phenomenon.
11. Table Cloth
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The table setting rests on a silk tablecloth. Rapidly yanking the
tablecloth out from under the setting pieces leaves the table
setting unchanged. The plates are at rest and want to remain at
rest.
12. Egg Spin
Observation
The hard-boiled egg will spin readily and stops soon after it is touched. But
the fresh egg is difficult to get spinning and once it starts moving it is
difficult to stop it from moving.
Result
Only the hard boiled egg spins readily since the mass inside it is solid and
evenly distributed. In the case of the raw egg, the liquid within causes a
drag effect that resists the spin initially and once the liquid is moving it
resists coming back to the state of being motionless. The egg that spins
readily and comes to a stop as soon as it is touched is the hard-boiled egg
hence.
13. Bike Tire
http://www.exploratorium.edu/snacks/bicycle_wheel_gyro/index.html
A rotating bicycle wheel has angular momentum, which is a property involving the speed of
rotation, the mass of the wheel, and how the mass is distributed. For example, most of a
bicycle wheel's mass is concentrated along the wheel's rim, rather than at the center, and this
causes a larger angular momentum at a given speed. Angular momentum is characterized by
both size and direction.
The bicycle wheel, you, and the chair comprise a system that obeys the principle of
conservation of angular momentum. This means that any change in angular momentum within
the system must be accompanied by an equal and opposite change, so the net effect is zero.
Suppose you are now sitting on the stool with the bicycle wheel spinning. One way to change
the angular momentum of the bicycle wheel is to change its direction. To do this, you must
exert a twisting force, called a torque, on the wheel. The bicycle wheel will then exert an equal
and opposite torque on you. (That's because for every action there is an equal and opposite
reaction.) Thus, when you twist the bicycle wheel in space, the bicycle wheel will twist you the
opposite way. If you are sitting on a low friction pivot, the twisting force of the bicycle wheel
will cause you to turn. The change in angular momentum of the wheel is compensated for by
your own change in angular momentum. The system as a whole ends up obeying the principle
of conservation of angular momentum.
Unfortunately, the gyroscopic precession of the wheel hanging from the rope is not explainable
in as straightforward a manner as the rotating stool effect. However, the effect itself is well
worth experiencing, even though its explanation is too difficult to undertake here. For more
information, consult any college physics text under precession.
14. Roto-rider
The sponge is forced by the cage into a circle. The water is
unaffected by the cage (the cage does not apply a force to it) so it
flies away from the sponge (in a straight line)
Water