Monday, February 28, 2011

Quick Labs

Some quick labs from one of the Honors Physics classes.  They conceived, designed, executed, and presented these on a white board in a period and a half (one period's the goal - we'll work on it!).
  • This group created a mostly empirical model relating the height to which an air track glider would rebound off of an elastic bumper, based on the height from which it was released.  They created a model of the "effective friction coefficient" based on the data, though they realized about halfway through that the bumper's probably the show, and that, with some more data, they could investigate the energy loss in the bumper as a function of v.

  • This group predicted how far a block would slide down a ramp (slowed by friction and a spring) before it stopped and was stuck by static friction.  

      Here are some "before" and "after" pictures: it was a pretty good prediction!


  • This group found the difference in the average force delivered with a "poke" and with a "flick" to a cart tethered by two springs. 

  •  This group predicted where a ball would land after rolling down a ramp and falling off of a table.  Their results were interesting: all were short, but the smallest solid balls were the best.  They made a surprising conclusion about rotational kinetic energy, which they hadn't even known existed before today!

      The balls' landing positions, with the roll of tape being the target:

  •  This group also tried a "ramp and hit the target" experiment.  They slid a mass down the ramp and tried to land in the foam catch box.

Friday, February 25, 2011

Quick Labs

Some more quick lab results:
  • Alex and Mike let an air track glider accelerate down an inclined track and fly off of the table, predicting where it would land (and placing a catch box there to protect my expensive gliders!).

Here are some videos of their attempts:
Success! (They realized that the end of the track has no air holes and slows the cart down a bit)
  • Haley and RJ tried to predict the amount that an air track bumper would compress while reversing the cart's motion.  They figured out that the rubber band isn't a linear spring, which colors their results a bit.

     A screenshot from them using Logger Pro and a video of the cart's turnaround to find the amount that the rubber band bent:

Wednesday, February 23, 2011

Quick Labs

Honors physics did some quick labs today - labs conceived, designed, executed, and presented on a white board within a single period.

Here's what they did:
  • Sandra and Jason - found the coefficient of kinetic friction between an air track and its glider, sans air!
  •  Danica and Steven - predicted how far a cart would roll down the ramp before being stopped by a spring
  •  Kati and Jayme - also determined the coefficient of kinetic friction between an air track glider and an air track, without the air on. 

Extra fun: why do you think that Jason's and Sandra's coefficient of friction was higher than Kati's and Jayme's?  Both are perhaps surprisingly high, but the track really stopped the carts surprisingly quickly!  Add your favorite theory in the comments!

Tuesday, February 15, 2011


Zach and Chris did a "quick lab" (conceived, executed, analyzed, and presented during a single class period) this week on the forces exerted on the basketball as Chris shoots a (perfect) shot.

In their own words:
The Question - "How much force (friction) is used to spin the basketball compared to the normal force used to propel it? "

The Design - "We recorded Chris taking a shot just short of the free throw line.  We analyzed the video on Logger Pro to determine the initial velocity and the acceleration of the ball.  We also were able to determine the angular velocity and acceleration of the ball. "

The Physics - "We used the known information to calculate the normal force on the ball from Chris's hand, and also the frictional force used to spin the ball."

The Whiteboard:

The Takeaway - "About 20% of the total force used to shoot the ball was used to spin it, and Chris's jumper is silky smooth."

Friday, February 11, 2011

On A Roll

Kyle and Joseph did a "quick lab" (conceived, executed, analyzed, and presented during a single class period) this week on the rotational inertia of a roll of masking tape.

In their own words:
The Question - "What is the moment of inertia of a roll of masking tape? What is the coefficient of the moment of inertia for the tape as compared to a uniform annulus?"

The Design - "2 ramps of different and changeable angles, one with the masking tape rolling and one with a frictionless object.  Angles are changed so that the two objects have the same acceleration."

The race is shown here: pretty much the desired tie.  The video's a little dark because it was shot at 300 fps.

The Physics - "We used the net torque and net force equations to solve for the inertia.  We used the linear acceleration to find the angular acceleration.  The coefficient of the moment of inertia is the moment of inertia divided by the mass multiplied by the radius squared."

The Whiteboard: 

The Takeaway - "Our moment of inertia calculation was a little bit off as compared to an annulus of the same dimensions, but not too far off. One of our assumptions was that the tape was of uniform density. Since the tape also had cardboard to keep its shape, our experimental moment of inertia was not completely accurate."