A large pendulum is pulled to one side and released from just in front
of your face. Upon return it will almost reach your face, so long as
have not moved. This shows conservation of mechanical energy. The sum
the bowling ball's gravitational potential energy and kinetic energy
constant. As it has no kinetic energy upon release it can get no higher
when it returns. When done as the first demonstration it lets you get
of the warnings dealt with at the beginning. I advise putting the back
of your head against a wall or upturned table so you know that you have
not moved forward.
You can spin around under the headgear while it stays stationary. It
Newton's first law, and it's cheap. Thanks to Paul Hewitt for this one.
Paper & Beaker
This is a classic demonstration of inertia, similar to pulling a table
cloth from under crockery. It has as much to do with friction as it
inertia. The beaker does not accelerate with the paper as that would
a force much larger than friction can supply. (No one is surprised that
the table doesn't move either!)
Air Puck and the Record Album Mini-version
Human air puck. The puck consists of a four foot diameter plywood disc,
the bottom of which is covered by a perforated plastic sheet. You can
either a leaf blower or a shop vac as the air supply. The design is
from an article that appeared in the November 1989 issue of "The
Teacher" page 615. Mini-version. The puck consists of an old record
album with an empty
sewing thread spool glued to its center. A balloon fits over the spool.
Table Cloth and Crockery
Make sure that your cloth does not have a seam along the edge being
under the crockery. The crockery will be set in motion, so don't put
too near the edge, nor use a table with a very "slick" surface, it's
cloth that needs to be slippery. Your local "thrift" store is a good
of crockery, choose dishes and glasses that have low centers of gravity
and smooth bottoms.
A more elegant version of the paper and beaker. If the hoop is not
the pen will only stand up easily when vertically above the bottle's
The sand or lead shot is for stability. It is important that the hoop
struck from the inside so that it forms an ellipse with a horizontal
axis. No friction is involved this way and if there's one thing you can
rely on, it's that gravity acts straight down. You can make a "mini"
of this using a section cut from a round, plastic gallon jug and a
Egg & Sheet
This is a graphic demonstration of the effectiveness of air bags and
they relate to Newton's second law. An egg can be thrown very hard at a
sheet held by two people. Have the helpers hold the sheet so that it
in a 'J' shape. Have some slack in the sheet and don't be afraid to
the egg hard, but don't squeeze it. A fitted sheet makes catching the
easier. A water balloon can be substituted for the egg if you're
Bike Wheel Twist
It is very difficult to twist a spinning bicycle wheel, especially if
tire of the wheel is filled with sand so the wheel has a large angular
momentum that needs a large torque to quickly change its direction. The
wheel needs handles fastened to its axle on either side. Commercial
are available. Be sure to wear a glove on the hand spinning the wheel
pick someone with fairly long arms and no loose clothing.
Bike Wheel and Lazy Susan
Hold a spinning wheel while standing on a turntable. Turn the spinning
wheel over, because of conservation of (zero) angular momentum the
rotates in the opposite sense to the wheel.
Skater on Lazy Susan
Hold a sandbag in each hand out at arms length while spinning slowly on
a turntable. When you bring your arms into your chest your rate of
increases showing conservation of angular momentum. Have your audience
just consider the speed of the sandbags. Sandbags are better than
as they don't hurt toes as much if dropped.
Bike Wheel Gyroscope
A spinning bicycle wheel hung by a chain from the axle on one side,
continue to rotate in the plane it was let go in. A vertical plane
well. It is effectively a gyroscope undergoing precession because of
being supported on one side.
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