This Java applet is a simulation of a ball rolling on a surface with kinetic friction. The user can vary the properties of the system to examine the transition from sliding to rolling without slipping. The center of mass velocity and the velocity of the edge of the ball are shown as functions of time as the ball moves.
Type of Material:
Java simulation with tutorial materials.
Recommended Uses:
Lecture/demo, Tutorial, Homework aid
Technical Requirements:
None noted
Identify Major Learning Goals:
Practice calculation of translational and rotational motion of a rolling object. Develop understanding of kinetic friction.
Target Student Population:
Lower level undergraduate
Prerequisite Knowledge or Skills:
Introductory mechanics, including friction, rotational motion, and torque.
Content Quality
Rating:
Strengths:
This is nice demonstration of rolling with and without slipping, and of the transition between one and the other. The initial center of mass velocity is fixed, but the angular velocity (actually, the angular velocity multiplied by the radius) and coefficient of friction are controllable by the user. The user can choose a spherical shell, or solid ball so as to vary the moment of inertia. An arrow in the applet shows the direction of the frictional force under the set conditions. The applet tracks the center of mass velocity and angular velocity of the ball graphically and numerically.
Concerns:
In the applet w (omgega) is positive for clockwise spin, different than for most right handed polar coordinate systems. The images in the simulation help to describe the situation.
The simulation correctly treats situations in which r*w0 is either less than V0 or greater than V0, but the text only refers to the first situation.
The equation for omega, w = w0 - t * (r u mg)/I (u is the coefficient of friction) in the text is wrong (it needs a plus sign instead of a minus sign in the sign convention used here) as long as r*w0 < V0.
It should be pointed out that the frictional force under consideration is the kinetic friction on the ball, and not static friction. Such distinctions are often unclear to students.
The radius of the ball and the units of r*w should be given so that students can more easily compare the numerical values generated by the applet with their own calculated values.
Potential Effectiveness as a Teaching Tool
Rating:
Strengths:
This simulation shows a ball transitioning from slipping to rolling without slipping,
which is not covered extensively in most undergraduate textbooks. This makes this material useful to supplement or extend standard curricula.
This applet can guide students to explore the transition to rolling without slipping conceptually as well as analytically by observing the motion under various initial conditions and then using the equations of motion to solve the problem. In addition, measurements of velocity and angular velocity can be made from the graphs with the mouse.
Concerns:
The instructions do not explain that the user can read values on the graph using the mouse.
This applet is somewhat limited in scope. There are not too many things that the user can do with it, especially as it pertains to quantitative problem solving.
While the applet works correctly, there are misprints and mistakes in the accompanying text.
Ease of Use for Both Students and Faculty
Rating:
Strengths:
The controls are pretty straight forward with drop-down menus for setting angular velocity and coefficient of friction.
Note: the user can pause the animation with the right mouse button, which is termed "toggle" in the instructions. The text accompanying the applet is divided into a section describing the physics and a section describing how to use the applet.
Concerns:
The variable rw might confuse students. Students might understand this better if they are told r is a constant and they are changing the angular velocity (w), and displaying r*w.
The graphs are a bit difficult to understand at first, but are useful.
There are a few problems with the grammar and spelling in the instructions.
Although perhaps obvious, the units of rw are not given.
"White arrow" should read "blue arrow" in the instructions.
Creative Commons:
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