They were moved along a wood plank while being attached to a 500-g spring scale in order to record the aloes when a) the block first moved, representing as and b) as it traveled at a constant speed, representing PC. In one experiment the wood block was placed on its side and the experiment repeated. Overall, the results showed that as > PC, and that the block that had the least surface area on the plank also had lower coefficients of friction when compared to one with more surface area on the plank.
Introduction The purpose of this experiment is to observe the friction force and to determine the coefficient of kinetic friction as well as static friction of materials of different snugness. Various types of materials were used, as well as horizontal versus inclined ramps. Friction occurs when two surfaces come into contact. The rough areas of each surface can come into contact and become cold-welded. Before an object can move over a surface, these cold-welds must be broken.
It is a non-conservative force; the force used to overcome the frictional force and allow an object to move is dissipated into heat energy and will not return to the system once the movement stops. Specifically, this lab will calculate the coefficient of friction. Unlike most efficient in Physics, friction behaves differently depending on whether the object is at rest or at motion. (Neat). This is due to the cold-welds formed as discussed above. Once the object is in motion, cold-welds cannot form so therefore force is not needed to break them as in the case of a static object.
The first case, the static coefficient of friction, FSP, is the force that keeps an object from moving. If there is an applied force too block, and the block remains at rest, then FSP = F. As the magnitude of F increases, FSP will increase proportionally until is exceeded. It is proportional to the normal force, N, acting on the block. The basic equation for the coefficient of friction is: FSP USN where as is the coefficient of static friction. If the block is just about to move, then FSP = FSML = USN. The force of friction is in the opposite direction of the movement.
To calculate the coefficient of friction, the following equation will be used: as = FSML/FAN Friction is actually a much more complex force than it appears from this introduction, or from the following sets of experiments. Intuitively it would seem that the smoother the surface, the lower the coefficient of static friction would come. However, it has been found experimentally that when two very smooth pieces of metal have been stacked together, given that all contaminates have been removed and they are placed in a vacuum, they become cold-welded and the coefficient of static friction is very high.
It has also been found that two sheets of smooth glass placed on top of each other have a higher coefficient of static friction than two sheets of roughly ground glass (Sings, 2007). For the case of the coefficient of kinetic friction, F fake if the block is moving at a constant speed. Once the force is removed that is causing the movement, he block will slow down and eventually come to rest. The only difference between the two coefficients is, once again, whether or not cold-welds have to be overcome. During movement those do not form, so PC< ps. Lastly, the case of an inclined plane will be examined.
Recall that the frictional force is proportional to the normal force acting on the block. The applied force acts perpendicular, normal, to the surface. The normal force is therefore calculated to be: N = (MGM) (coos 9) From this diagram, we can see the as = FIN, where F = MGM*sin 8 and N = MGM*coos B. Therefore as = MGM*sin e/ MGM*coos e, or tan 9 (Screwy, 1994). For measuring purposes, tan 6 = height/base which will make the calculations much easier. The length of the plank is known, and the height can be measured. Using the Pythagorean Theorem, the base can be calculated and then used to determine as.
Methods Materials: Ramp board, 4 feet long set at 10 CM off the ground. Can of soup 500-g spring scale Meter tape Friction block set (one wood, one glass, one sandpapered) Protractor Procedure:2 part 1 1. A can of soup will be used to add weight to the friction blocks. Weigh the plain wood block and the can of soup. Record the combined weight in grams and Newton’s. 2. Place ramp board horizontally on a table. Secure the board so that it does not slide. 3. Set the block and soup can on a board with the largest surface of the block in contact with the surface of the board.
Connect the block’s hook to the 500-g spring scale. 4. Using the spring scale, slowly pull the block lengthwise along the horizontal board. When the block is moving with a constant speed, note the force indicated on the scale and record. Repeat two more times. 5. While carefully watching the spring scale, start the block from rest. When the block just starts to move, note the force on the spring scale and record. Repeat two more times. Part 2 1. Turn the wood block on its side. 2. Repeat the entire process from Part 1 three times and record the force of kinetic and static friction for each trial. Part 3 1 .
Determine the force of kinetic and static friction for the glass surface and sandpapered surface blocks. 2. Repeat Parts 1 – 3 with at least two flat surfaces around the lab such as rubber, tile, cork, etc. Record the findings in tables similar to Data Table 3. Part 4 1 . Place the plain wood block with the largest surface in contact with the board while the board is lying flat. 2. Slowly raise one end of the board until the lock just breaks away and starts to slide down. Be very careful to move the board slowly and smoothly so as to get a precise value of the angle of repose, Beam. Measure with the protractor and record the result.