Movie of the spinning plant

A bulb plant is grown while spinning on a platform 24/7.  This is clearly hard on the player, so don't expect to play records after using one like this.  I use a dedicated record player set to 45 or 78 rpm (usually 45).  With the added resistance, the result is much lower than 45 rpm.  Watering is done by unplugging, slowing it down to a stop, watering, spinning it back up and re-plugging it in - as you'd expect.

The goal for the class is to use measurements from the video (or live demo usually) of radius and time (use 10 revolutions) to determine the centripetal acceleration, v^2/r.  Then, use this as a component along with g, to predict the angle the plant should be growing at.  The growth hormones at the base of the bulb are 'sloshed' through the cells to promote growth on the outside and bottom.  The growth hormone would usually be evenly distributed near the bottom, hence the growth from the base.  The plant does not grow straight up because more growth hormone is away from the center and the outside cells then multiply faster.  Light for energy in growth is removed as a factor because of the spinning, and the shoots grow much straighter and are clumped more narrowly because of the increased total acceleration making for an easier angle measurement.  The growth angle of the plant as a whole does not change due to the fact that the growth is only at the base at one location - so it grows straight.  I made a large overhead of the image to measure the angle with the class while they did the same on 1/2 sheet handouts.  Although I go through this together, one could use a handout and video file with small groups.

You may find this useful if using the video or plan on doing this:
The radius for the platform (1x4 board)  is 0.565 meters; this size works well with a smallish pot.
Note the hole drilled in the center to fit onto the player (Centripetal.jpg).  The pots are bolted onto the board with oversized fender washers inside the pots.
The plant is a Paperwhite (bulb), aka Narcissus.  The advantage is the quick growth.  Plant the bulbs, keep them moist, and you have a plant that looks like the spinning image in a little over a week.  In three weeks, the top blooms and becomes top-heavy, then flops over.  Bulbs are generally available at the stores in fall and spring only; Paperwhites sell out relatively quickly.

When the live plant demo doesn't quite work (sometimes my bulbs get mushy by the time I am ready for this), I use this video.

Other Notes:
A lead-in to this could be the toys that hang from the ceiling.  It is much easier to set up a toy then to grow the plant and it takes up less space (and doesn't have to be a possible distraction for over a week).  A video and image (paused from video taken in class is fine) can then be used along with a classroom-sized protractor on the projected screen (whiteboard) or television works great.  Examples are superheroes (Fusion Toys), airplanes, space shuttle, helicopters (all D.Y. Toys), or even flying pigs.  I bought all of mine from a store at the Mall of America in Bloomington, MN.  I used to do a lab on this, but it wasn't elegant enough to really get good results and make good connections for the students.  It's better as a demo or lab demo to see the relationship.  If you make your own video, include a meterstick in the video or something to set the scale, make sure the camera angle is at the same level, and place something conveniently behind (within the circular path not necessary...) to 'measure' the spinning against.  You may want to use pots of two very different colors if using plants for counting or reference.  I've never used anything but Paperwhites, but perhaps something fast growing like chives or even grass (may) work, if only for effect.  I think it needs to grow from the base?  I plan on growing a row of whatever I can get ahold of to see if we can get an angled effect.  I use this same set-up then with a candle in a beaker to discuss what direction the flame should point, or a ping-pong ball buoyed with bright yellow cord to the bottom...


Dan Hagstrom
Mount Horeb

Still Powerpoint Print out for students to do angular calculations

Overhead Powerpoint use to show the plant angle


Files attached are
* 2 Mb video - Remember there are two plants spinning although you can only see one at a time... (use the cabinet doors for start/stop on the stopwatch)
* image of identical bulb plant grown normally
* image of spinning toys I have used in lab
* still image from the video
* PowerPoint file for 1/2 sheet handouts for kids to measure angle
* PowerPoint file for full size overhead transparency