# Lab Report: Friction

Topics: Friction, Force, Classical mechanics Pages: 6 (1729 words) Published: September 6, 2010
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INTERPRETATION OF RESULTS
In the last experiment, relation between mass of an object or the net force with acceleration was defined. Another type of force acting on a system is to be discussed in this experiment. When two objects interact by touching or contacting each other, interaction is said to be subjected to contact forces. Among those contact forces, we have normal force and frictional force. Normal forces are forces acting perpendicularly towards the object. It is due to molecules of the surface is resisting the molecules of the object squeezed on it. Principal concern in this experiment is the frictional force. The use of oil in a cart engine, the use of right lubrication in skating as well as in basketball, the screeching sound of a sudden stopping car are all occurrences which is exploited by friction in the reality. Meanwhile, frictional force is component acting on them. It acts parallel to the interface or the surface of contact. Furthermore, this force acts to oppose any relative motion between surfaces. Thus, it is a force which resists the relative motion of one surface in contact with another. This force is not only exerted by one object but between the contacting surfaces. One good example of this is the air drag – the frictional force exerted by the air on body moving through it. Frictional force is occurring in the same way as the normal force. When an object is laid on a surface, molecules of the object will form very little bonds with the molecules of the surface. First part of the experiment deals with the determination of coefficient of friction of motion of a moving object. Tension force pulling the wooden block is associated by mass carried by pan and the gravity. It is gradually increased until object moves with constant velocity. At those times that the object is not yet moving, static frictional force is present. It is not constant. We added some load but still, it is not yet moving. By that, static frictional force is equal to the force to the tension force applied thus, capable of contradicting the force. The static frictional force will continually increase as load is added until it reaches the maximum force that the static frictional force can exert. It is also known as (fs)max. When a frictional force is at its maximum, the body in question will either be moving or will be on the verge of moving. At this point, when the object starts to move with constant velocity, the frictional force will be present is now kinetic frictional force, f k. It is easier to move an object in motion rather than starting with stationary object. It is because fs > fk ,usually. In connect with this, we have coefficient of friction is represented by symbol µ which is a dimensionless scalar value. The coefficient of friction (static or kinetic) is a measure of how difficult it is to slide a material of one kind over another; the coefficient of friction applies to a pair of materials and not simply to one object by itself. The coefficient of kinetic friction is usually less than compared to static frictional force. It is the reason why fs > fk because µs is usually smaller than µk. On static frictional forces, its coefficient starts at zero, increasing depending on the force applied until it reaches it maximum value. Thus it is correct to interpret that the static frictional force is given by fs ≤µsN and the kinetic frictional force is given by f k µkN. In the experiment, the kinetic coefficients (since friction is measured when object starts to move constantly) we had calculated are: 0.562, 0.502, 0.493, 0.519, and 0.515 giving an average of 0.5062. This coefficient is extremely independent with the weight of the object and the normal force. It is dependent with two contacting materials because of their different attraction and repulsion with each other. By increasing the surface area starting on the third trial, we could get the same frictional force. Thus,...