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Here are some more possible ideas to explore and explain the balls on ramps.

What are some questions students can ask to determine what is happening?:

Do the balls start at the same place?  Do they end at the same place?

Are there places where one ball speeds up (accelerates) faster than the
other ball?

If one ball speeds up and moves faster than the other, is there a period of
time when it is traveling faster than the other ball?

When the ball that moves faster goes back uphill, does it slow down?  If it
slows down, is it moving faster, slower, or the same as the other ball at
the same point on the track?

When the balls get to the end of the tracks, which one rolls furthest on a
flat surface - or do they both roll the same distance?

What if we start at the bottom of the ramps and push the balls up the ramps?
How far does each go if we give them equal pushes?  Which returns to the
bottom first?

Can we place the balls at different starting points so they reach the bottom
at the same time?

What if we have horizontal ramps (one  straight and flat and the other with
a dip in the middle) so that we need to push the balls to get them to roll
(the dip goes downhill, travels a distance, and then goes back uphill to the
horizontal surface)?  How do the speeds of the balls compare at different
places?



Quick simple explanation for staff:

The kinetic or moving energy and thus the velocity (or speed) of the ball at
the bottom is a function of how far the ball falls (distance from the
release point straight down to the floor). So both balls should moving at
the same speed at the end of the ramp if the ends of the ramps are at the
same height or place since both balls fall the same distance even thought
they roll much greater distances. Friction is ignored in this explanation.

When rolling down the ramp because of the force of gravity, one ball speeds
up because is goes down a steeper hill. It then travels at a distance at a
faster speed than the other ball - and thus moves ahead of the other ball.
When the faster ball goes up hill is looses its advantage but it is ahead of
the other ball because it moved faster for a period of time. It turns out
that, in this case, moving faster offers a grater advantage than the
disadvantage of moving further.  If you could measure the speed of the ball
on the straight ramp at the point where the faster ball returns to the same
height as the slower ball, the balls would be traveling at about the same
speed at that point on the ramps (and both would be traveling faster than
they where when the one ball dropped into the dip).

Hope this helps.

Bill Schmitt











-----Original Message-----
From: Informal Science Education Network
[mailto:[log in to unmask]]On Behalf Of Jonah Cohen
Sent: Monday, December 05, 2005 12:11 PM
To: [log in to unmask]
Subject: Let it Roll


ISEN-ASTC-L is a service of the Association of Science-Technology Centers
Incorporated, a worldwide network of science museums and related
institutions.
****************************************************************************
*

OK, here's a question for ya...



Say you've got an exhibit where two balls roll down tracks. One goes down a
straight inclined plane (maybe a 40 degree angle), the other goes down a
wavy path (steeper slope in parts, but also some uphills). You may well have
this exhibit at your center.



Experiment shows that the ball on the wavy track hits the bottom first, even
though it has to travel further. But reconciling theory to experiment is
where it gets dicey. Why does this happen? We've had detailed debate on this
and what should be in the signage.



And ironically, this exhibit is in our kids area. Draw what conclusions you
will from that about concept + process.



Help me, fellow physics geeks!

Jonah Cohen

Outreach & Public Programs Manager

Science Center of Connecticut



"On blind faith they place reliance,

what we need more of is science"

           -MC Hawking




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