Friction Lab Study

Physics 121/145 Friction Lab

In this report, I will be exploring several aspects of the current Friction lab

• Does the wiping of the track effect the amount of static friction during static prodedure
• Does the wiping of the tack effect the amount of kinetic friciton during the kinetic procedure
• Create a procedure to capture frictional loss, accounting for several factors
• Measure the effect of the vander walls force by applying force to the friction cart over several iterations.

Wiping the track/ Vander Waals force

I created an experiment to measure the effect of wiping the tracks in order to determine which type of rag is needed in order to prepare the friction experiment.

The repeated process was to level a track, attach the cart/felt friction block to a modified atwoods machine and then add weight until static friction was overcome.

There were three phases to this experiment: 1. Complete measurement with a track that had not been cleaned since it was last used. (at least a month) 2. Complete measurement after the cart/friction block had moved at least once, followed by running the cart back and forth over the track as well 3. Complete measurement after thouroughly wiping off the track with the static free rags

This experiment was tested with 5 randomly selected tracks

ggplot(fric_dat%>%filter(run_once == 'T'), aes(y = grams , x = wiped))+geom_boxplot()+ggtitle('Distribution of Force to Overcome Static Friction When Track is Wiped')

The graph of the distributions of force over 5 events shows that wiping the track does not seem to have any impact on the force that needs to be applied to overcome the static friction once the experiment has been completed at least once.

pre_treatment<-fric_dat%>%filter(run_once =='T' & wiped =='F')%>%select(grams)
post_treatment<-fric_dat%>%filter(run_once =='T' & wiped =='T')%>%select(grams)

t.test(pre_treatment,post_treatment)

## 
##  Welch Two Sample t-test
## 
## data:  pre_treatment and post_treatment
## t = 0.4416, df = 9.9848, p-value = 0.6682
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
##  -6.744468 10.077801
## sample estimates:
## mean of x mean of y 
##  40.66667  39.00000

A hypothesis test confirms that there is no difference between wiping and not wiping the track with the rag.

Effect of running the experiment once on Static Friction

ggplot(fric_dat, aes(y = grams , x =run_once))+geom_boxplot()+ggtitle('Distribution of Force to Overcome Static Friction Before and After Experiment is run once')

pre_treatment<-fric_dat%>%filter(run_once =='F' )%>%select(grams)
post_treatment<-fric_dat%>%filter(run_once =='T' )%>%select(grams)

t.test(pre_treatment,post_treatment)

## 
##  Welch Two Sample t-test
## 
## data:  pre_treatment and post_treatment
## t = 2.2358, df = 6.6882, p-value = 0.0622
## alternative hypothesis: true difference in means is not equal to 0
## 95 percent confidence interval:
##  -0.733504 22.400171
## sample estimates:
## mean of x mean of y 
##  50.66667  39.83333

The plots and t-test confirm that there is likely an effect on the force of the static friction when the experiment is run at least once prior to measurement.