# Physics Lab

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Date Submitted: 05/15/2012 10:18 AM

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Physics lab II

Coefficient of static and kinetic friction

Aim:

To find coefficient of static and kinetic friction between an object and its surface

Theory:

For µk

∑Fy = N-m∙g∙cos(x )= 0

N= m∙g∙cos(x)

∑Fx = m∙g∙sin(x) -µk m∙g∙cos(x) = m∙a a= 2∆x/t^2

µk= g∙sin(x)- a/ g∙cos(x) ∆x=at^2/2

µk= tan(x)-2∆x/t^2 ∙ g∙ cos(x)

For µs

m∙g∙sin(x)= Fs= µs∙m∙g∙cos(x)

µs= tan(x)

Materials:

-Stop watch – measuring tape –wooden board- a metal object- protractor

Procedure:

For kinetic friction:

At a constant distance of the wooden board, measure the time it takes for the metal piece to hit the ground at several different angles. In this experiment we tested the time for 6 different angles.

For Static friction:

Raise the wooden slowly with the metal piece at the very end of the board. Measure the angle in which the piece starts to move. Repeat 5 times and average the result.

Observations:

|  angle | T1 | T2 | T3 | T4 | Tavg | Tavg squared |  Uk |

0.85m | 45 | 0.58 | 0.40 | 0.47 | 0.58 | 0.507 | 0.257 | 0.046 |

0.85m | 60 | 0.50 | 0.42 | 0.45 | 0.47 | 0.46 | 0.2116 | 0.093 |

0.85m | 67 | 0.48 | 0.46 | 0.42 | 0.42 | 0.445 | 0.198 | 0.1149 |

0.85m | 70 | 0.59 | 0.37 | 0.50 | 0.50 | 0.49 | 0.240 | 0.635 |

0.85m | 79 | 0.41 | 0.48 | 0.40 | 0.44 | 0.43 | 0.1849 | 0.23 |

0.85m | 80 | 0.40 | 0.48 | 0.45 | 0.45 | 0.445 | 0.198 | 0.63 |

Average  Uk  = 0.29

angle 1 | angle 2  | angle 3  | angle 4  | angle 5  | angle average  |

30º | 27 º | 29 º | 28 º | 23 º | 27.4 º |

Results/Calculations:

Analysis:

Some errors would have been that we didn’t measure the angles accurately, not having a fast reflex when the metal piece hits the ground, making errors while calculating the results. The results we calculated are quiet acceptable compared to the actual kinetic friction of a wooden board and a metal piece because it ranges from 0.2 to 0.6 and our...