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# Lab_3 - Phys 151 F04 Name_Duties Name_Duties Name_Duties...

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Phys 151 F04 Lab 3 Name ______________   Duties ______________________________________ Name ______________   Duties ______________________________________ Name ______________   Duties ______________________________________ For this lab you will complete two exercises. Below are the prelab write-ups that you should read and understand before you show up for the class. Print a copy and bring along to the lab . Title : Slip Sliding Away! Oh, Friction is so “Triggy” Purpose : To understand friction and its characteristics. Concept/Theory : Friction is the force that "kicks in" to oppose the relative motion of two surfaces that are in contact. When an object is placed on an inclined plane, gravity will try to drag it down. That’s why hilly slopes are a skier’s paradise. However, you know that nothing happens if the slope is too gentle. And weight seems not to matter either. A heavier person is just as likely to remain “stalled”. Gravity is still acting so what gives here? It’s because another unseen force is present, namely friction and, since it exists mainly to oppose motion, friction between the object and the slope works here to negate the effect of gravity. But why did you not remain stalled when the slope is steep? That’s because friction (which grows to match whatever is needed to prevent motion) cannot exceed a maximum value for a set mass. (This is similar to what happens with a rubber band that stretches until the elastic limit is exceeded, when it snaps.) If the weight is increased (with the surfaces in contact remaining unchanged) so is this maximum value increased but their ratio (directly related to a number called the coefficient of friction of the two surfaces) does not change. Thus for a given slope, weight (in general) does not change an object’s inclination to move. There is one other factor that plays a role in this “ski-namics”. If you wax your skis you have a distinct advantage. That is because how large friction is depends upon the nature of the two surfaces in contact. In this

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Lab_3 - Phys 151 F04 Name_Duties Name_Duties Name_Duties...

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