MAR-16-2015 Modeling Friction Forces

Modeling Friction Forces: Part 1

(Static Friction)

Purpose:  This lab is broken into five sections, each dealing with either static or kinetic friction between the felt on the bottom of a block and the surface it's traversing.  We will be gathering data using motion sensors and force sensors for specific sections of this lab.

Procedure:  We first determined the mass of a single block (the one with the felt bottom) which we measured to be 121 g.  We then tied a string to the block, with the opposite end running over a pulley at the end of a table attached to a bent paperclip, which is in turn attached to a Styrofoam cup.  This setup is depicted below.

(Part 1 initial setup)

We then began to add small amounts of water into the cup.  This was continued until there was JUST enough water in the cup to cause the system to begin to move.  Once this occurs, we measured the mass of the cup and water to be 34 g.  

(The cup, bent paper-clip, and water combined mass JUST starts to move the system)

Next, we measured the mass of a second block, and stacked it on top of the original.  We then added more water into the cup until this new system JUST began to move.  This process was repeated until a total of four blocks were stacked upon each other.  Depicted below is a graph which contains the Normal force as the x-axis, and the force of static friction as the y-axis.

(LoggerPro linear fit graph of data collected)

The above graph shows that the slope of this line is the coefficient of static friction, and that value is 0.3712.  Below is handwritten work regarding the same data.

(Work for Part 1 of lab)

Modeling Friction Forces: Part 2

(Kinetic Friction)

Procedure:  In this section of the lab, we used a force sensor in order to determine the force of a constant pull on a block of wood traversing a surface.  First, we calibrated the force sensor using a 500 g hanging mass.  We then determined the mass of the wooden block that has felt on it's lower surface.  We held the force sensor horizontally and zeroed it.  Afterwards, we tied the force sensor and wooden block together with string.  We then used LoggerPro software to record and analyze the average force exerted on the block during a pull at constant speed.  In order to get an average force value, we used the Analyze menu in LoggerPro, then selected Statistics, then recorded the mean value of the pulling force.  This process was repeated for a total up four block stacked upon each other.  The LoggerPro graph is depicted below.

(LoggerPro linear fit graph for part 2 of lab)

It appears the above graph is incorrect in nature, as I doubt the coefficient of kinetic friction is 0.020. The data I received from a lab partner was perhaps corrupted when transferred.  The above graphs were made at home without the aid of experimental equipment.  I'll attempt to rectify this portion of the lab post-haste.

Modeling Friction Forces: Part 3

(Static Friction From A Sloped Surface)

Procedure:  We placed a block on a horizontal surface, and then raised one end of the surface until the block JUST started to slip.  At this point of maximum static friction, we recorded the angle between the horizontal and tilted surfaces.  Below is the work done to calculate the coefficient of static friction between the block and the surface it was attempting to traverse.

(Determining the coefficient of static friction)

Modeling Friction Forces: Part 4

(Kinetic Friction From Sliding A Block Down An Incline)

Procedure:  We placed a motion sensor at the top of an incline which was steep enough to cause the weighed block to accelerate downward.  Recording the angle at 20.6 degrees above the horizontal.  The physical setup as well as the solution are pictured below.

(Inclined surface at 20.6 degrees above the horizontal)

(Solution for coefficient of kinetic surface)