Lab 09

Lab 9: Static, Kinetic, and Rolling Friction on Inclined Surfaces Laboratory Report Data Table 9.3 Surface Trial μ s μ k μ r Cardboard 1 .243 .228 .213 2 .293 .239 .206 3 .307 .275 .224 Cork 1 .299 .282 .192 2 .271 .243 .199 3 .261 .236 .195 Rubber 1 .674 .304 .227 2 .710 .346 .263 3 .646 .282 .238 Sandpaper 1 .364 .179 .260 2 .353 .222 .231 3 .343 .264 .227 Data Table 9.4 Surface Avg. f s Avg. f k Avg. f r Avg. μ s Avg. μ k Avg. μ r Cardboard .787 .694 .602 .281 .247 .214 Cork .777 .711 .549 .277 .253 .195 Rubber 1.89 .871 .682 .676 .311 .242 Sandpaper .991 .621 .672 .353 .221 .239 Data Analysis Question: Which surface had the higher static, kinetic, and rolling friction. Why is this the case? Support your answer with your data. Rubber had higher static, kinetic, and rolling tension because of the adhesion the rubber creates between surfaces, and it required a greater amount of weight to move it.

Lab 9: Static, Kinetic, and Rolling Friction on Inclined Surfaces Laboratory Report 2. What other factors do you think could also play a role in why rolling friction is less than sliding friction? The area of contact between the surfaces and the smoothness or roughness of the surfaces 3. Explain the effect of gravity on a wheel in relation to rolling friction up an incline compared to attempting to pull (dragging) a block up an inclined plane. The force of gravity would be the same in either instance, but the force of friction would be different 4. Would 12 N of pulling force be enough to pull a 10 kg block up a 25° incline that has a coefficient of static friction of .89 and a coefficient of kinetic friction of .65? Support your answer in the space below. No; 𝑇 = 𝑚𝑔 sin 𝜃 + 𝜇𝑚𝑔 cos 𝜃 ; 10(9.8)(sin 25) + (.89)(10)(9.8)(cos 25) = 120.5 N 5. Would 12 N of pulling force be enough to pull a 10 kg block across a horizontal version of the surface in problem 4? Support your answer in the space below. No; f = μ mg; (.89)(10)(9.8) = 87 N Error Analysis The first error was caused by a higher inclination in the track. The recommended incline given was between 15° – 25 °, but because of how the setup had to be done, the incline of the track was 30°. However, as the incline increases, there is a greater component of gravitational force acting on the object causing acceleration. In this experiment, there should be no acceleration because it changes the value of the required tension. This error could have been the reason for the percent errors higher than 20%. The second error occurred while recording the tension of the cart on the sandpaper. Due to the sandpaper being used multiple times, the sandpaper had worn down a little bit causing the surface to not be as rough. This affected the amount of tension required to pull the cart on this surface and can be seen in the percent error for the coefficient of the static and kinetic friction which were 47.1% and 57.9% respectively. The third source of error is the lack of consideration of the friction from the pulley and the string. In order for the experiment to be executed correctly, the string had to be level and not at an angle. However, because the levelness of the pulley had to be measured with the human eye, there is a chance for error. If the string creates an angle, then the friction would be increased/decreased. The percent error was high for some of the surfaces, and this error could have been a contributing factor.