Kinetic Friction

Experiment 4: Friction Laboratory Report Anna Rucelli Ignacio Michael Giorgio Lapus Ted William Lardizabal Janell Leica Lee Department of Occupational Therapy College of Reabilitation Sciences, University of Santo Tomas Epa, Manila Philippines Abstract The experiment verifies the laws of friction with the use of a spring scale, a block of wood, its different surfaces and the different surfaces of other objects. Another part of the experiment uses the palms of the hands to produce friction then apply lubricants then see the differences.

The experiment also observes the effect of air resistance on falling paper. 1. Introduction Friction is the force resisting the relative lateral (tangential) motion of solid surfaces, fluid layers, or material elements in contact. It is usually subdivided into several varieties: * Dry friction resists relative lateral motion of two solid surfaces in contact. Dry friction is also subdivided into static friction between non-moving surfaces, and kinetic friction (sometimes called sliding friction or dynamic friction) between moving surfaces. Lubricated friction or fluid friction resists relative lateral motion of two solid surfaces separated by a layer of gas or liquid. * Fluid friction is also used to describe the friction between layers within a fluid that are moving relative to each other. * Skin friction is a component of drag, the force resisting the motion of a solid body through a fluid. * Internal friction is the force resisting motion between the elements making up a solid material while it undergoes deformation.

Friction is not a fundamental force, as it is derived from electromagnetic force between charged particles, including electrons, protons, atoms, and molecules, and so cannot be calculated from first principles, but instead must be found empirically. When contacting surfaces move relative to each other, the friction between the two surfaces converts kinetic energy into thermal energy, or heat. Contrary to earlier explanations, kinetic friction is now understood not to be caused by surface roughness but by chemical bonding between the surfaces.

Surface roughness and contact area, however, do affect kinetic friction for micro- and nano-scale objects where surface area forces dominate inertial forces. The normal force is defined as the net force compressing two parallel surfaces together; and its direction is perpendicular to the surfaces. In the simple case of a mass resting on a horizontal surface, the only component of the normal force is the force due to gravity, where N=mg. In this case, the magnitude of the friction force is the product of the mass of the object, the acceleration due to gravity, and the coefficient of friction.

However, the coefficient of friction is not a function of mass or volume; it depends only on the material. For instance, a large aluminum block has the same coefficient of friction as a small aluminum block. However, the magnitude of the friction force itself depends on the normal force, and hence the mass of the block. If an object is on a level surface and the force tending to cause it to slide is horizontal, the normal force N, between the object and the surface is just its weight, which is equal to its mass multiplied by the acceleration due to earth’s gravity, g.

If the object is on a tilted surface such as an inclined plane, the normal force is less, because less of the force of gravity is perpendicular to the face of the plane. Therefore, the normal force, and ultimately the frictional force, is determined using vector analysis, usually via a free body diagram. Depending on the situation, the calculation of the normal force may include forces other than gravity. [pic] A common way to reduce friction is by using a lubricant, such as oil, water, or grease, which is placed between the two surfaces, often dramatically lessening the coefficient of friction.

The science of friction and lubrication is called tribology. Lubricant technology is when lubricants are mixed with the application of science, especially to industrial or commercial objectives. Superlubricity, a recently-discovered effect, is the substantial decrease of friction between two sliding objects, approaching zero levels. A very small amount of frictional energy would still be dissipated. 2. Theory ?s = maximum static friction normal force ?K = kinetic friction normal force 3. Methodology

For the first activity, a piece of wood was placed on top of a wooden board with a spring scale attach to it. The minimum force needed to start the motion was determined by pulling the spring balance which is numerically equivalent to the maximum static friction. The kinetic friction was determined by pulling the spring balance with constant motion. This procedure was repeated by using the other sides of the block and their fsmax and fK was recorded. For the first trial in the second activity, the fsmax and fK of the wooden block was determined.

For the succeeding trials, 100g weight is added to the block every trial and their fsmax and fK was recorded. This was called the normal force which is equivalent to the weight of the block plus 100g. After getting their fsmax and fK, their µs was calculated by using the formula µs = fsmax/fn. Also the µK was calculated by using the formula fK/ fn. For the first trial of the third activity, the fsmax and fK of the wooden block was determined while it was pulled over a wooden board. In the second trial, the wooden surface/board was replaced with the tiles of the floor.

So the wooden block was pulled over the tiles of the floor and its fsmax and fK of the wooden block was recorded. For the third trial, sand paper was used as surface while the wooden block was pulled and its fsmax and fK was recorded. For the next trial, plastic cover was used as surface while the wooden block was pulled and its fsmax and fK was recorded. Lastly, paper/cartolina was used as surface while the wooden block was being pulled and its fsmax and fK was recorded. For the fourth activity, one member of the group was asked to rub his/her hands together for one minute.

After rubbing, was asked to place his/her hands on his/her cheeks and the sensation felt was observed. The succeeding trials were done by applying powder, oil, and lotion before rubbing the hands. The sensation felt was also recorded. For the last activity, a paper was dropped over a motion detector and its terminal velocity and square of terminal activity was recorded by using a program installed in the computer. The following trials were done by adding 1 paper every trial on top of each other and were dropped on the motion detector. Its terminal and square of terminal velocity was recorded.