The Physics of a Falling and Unrolling TP Roll

Submitted by Rich on Mon, 06/26/2017 - 17:57

Yes, that's right--the physics of a falling and unrolling toilet paper roll.  This experiment will give students practice in rotational motion of an object and translational motion of its center-of-mass.  It will also involve both the kinematics and dynamics of the motion. While it can be done by use of the VelocityLab app, interpretation of the angular velocity data from the PocketLab app is much easier.

A Velocity Lab Experiment on Rolling Resistance

Submitted by Rich on Mon, 06/26/2017 - 17:45

Rolling resistance is a force that opposes the motion when an object rolls along a surface.  In this experiment a coasting cylinder on a carpet gradually slows down and stops due to rolling resistance.  The primary factor affecting rolling resistance here is deformation of the carpet as the cylinder rolls.  Not all of the energy needed to deform the carpet is recovered when the pressure from the cylinder is removed.  In other words, the effect is non-elastic.  The purpose of this experiment is two-fold:  (1) to determine the force of rolling resistance and (2) to determine the coefficient o

VelocityLab Investigation of Damped Harmonic Motion

Submitted by Rich on Mon, 06/26/2017 - 17:28

This investigation shows how VelocityLab allows for a quick and easy demonstration of damped harmonic motion.  The photo below shows the experiment setup as performed by the author.  A jellied cranberry sauce can was selected as there is virtually no sloshing of the cranberry sauce as the can oscillates back-and-forth on a curved piece of laminate flooring.  The center of the flooring is clamped down to the table with an adjustable wrench.  The ends of the laminate flooring are raised a little with some small wood blocks.  The cranberry sauce can is shown at rest at the VelocityLab zero pos

Using VelocityLab in an AP/College Physics Experiment Involving Rotational Dynamics

Submitted by Rich on Tue, 06/20/2017 - 23:42

This experiment is designed for AP Physics and college physics students.  It considers a solid cylinder of mass M and radius R that is rolling down an incline with a height h without slipping.  Using energy and dynamics concepts, students first derive equations for (1) the speed of the center of mass of the cylinder upon reaching the bottom of the incline, and (2) the acceleration of the center of mass of the cylinder as it rolls down the incline.  The free-body diagram at the center shows all forces acting on the cylinder as it rolls down the incline.

A PocketLab Experimental Analysis of a Yo-yo

Submitted by DaveBakker on Tue, 06/20/2017 - 22:20

The yo-yo, a toy with an axle connected to two disks and string wound on the axle, has been of fascination to many for centuries.  It also offers a perfect opportunity to study angular velocity when a PocketLab has been attached to it.  A graph of angular velocity vs. time of a yo-yo will require students to think carefully about the detailed behavior related to its motion.

Rotational Dynamics of a Falling Meter Stick

Submitted by Rich on Fri, 06/16/2017 - 19:29

There is a well-known problem in rotational dynamics that involves a meter stick.  The meter stick is held in a vertical position with one end on the floor.  It is then released so that it falls to the floor.  The end initially on the floor is not allowed to slip during the fall.  Students are asked to derive an equation that predicts the angular velocity of the meter stick just before it hits the floor.  The derivation involves many physics concepts including gravitational potential energy, rotational kinetic energy, conservation of energy, moment of inertia, and angular velocity, thus giv

Magnetic Field on the Axis of a Current Loop

Submitted by Rich on Thu, 06/15/2017 - 22:17

In this lesson students will find that a current-carrying loop can be regarded as a magnetic dipole, as it generates a magnetic field for points on its axis.  The figure below shows a diagram and the equation for the magnetic field B.  Derivation of this equation requries knowledge of the Biot-Savart Law, calculus and trigonometry.  But in this lesson we are interested only in comparing experimental results from PocketLab's magnetometer to the theoretical equation in the figure below.  More advanced students can consider derivation of the equation, if they wish.

A Quantitative Study of Helmholtz Coils

Submitted by Rich on Thu, 06/15/2017 - 22:05

These coils come in pairs with the same number of windings of wire on each of the two coils. In "true Helmholtz" configuration: (1) the coils are wired in series with identical currents in the same direction in each coil, and (2) the coils are placed a distance apart that is equal to the radius of each coil. When in this configuration, they produce a very uniform magnetic field that is directed along their common central axis.