Влияние адгезии на трение качения и скольжения: эксперимент

Normal and tangential contact between a cylindrical steel indenter (wheel) and an elastomer with high adhesive properties is investigated. In the case of indentation in the normal direction, a computer simulation of the process of indentation and detachment was carried out, which shows good coincidence with an experiment. For the rolling friction mode, when analyzing the measured dependences of the tangential component of the contact force on the wheel displacement, the adhesive component of the friction force was determined. The situation of sliding friction, in which the rotation of the wheel was impossible, is considered. In the presence of adhesion, the sliding friction force is proportional to the contact area. In the absence of adhesion (the elastomer is covered with a chalk dust), a stick-slip friction mode is realized. The frequency and amplitude of stick-slip transitions depend on the indentation depth of the indenter into the elastomer.

Detection and Erasing Scribble Blackboard System Based on Hough-Transform Method Using Camera

Teachers of a secondary school in Semarang city are often exposed to blackboard chalk dust. This will give a significant impact if it occurs at a fairly frequent intensity and a long period of time. An automatic scratch detector and designing a device that can erase the blackboard is a preventive step that can reduce the long-term impact of chalk dust. The scratch detector uses a circle shape parameter as a mark of dirty position that needs to be erased. Light can affect the system performance. The system works properly at light intensities ranging from ± 160 to ± 200 lux. Testing the threshold value proves that the system can detect circles in the range of 40 - 55. The pixel size which is detected by the camera was 640x480 will allow the system to divide the blackboard into 9 mapping areas. The mapping area is differentiated into 9 sections so that the x and y coordinate positions of the blackboard dirty spot can be determined. A mechanical execution will erase the top and bottom areas according to the position of the detected mapping area. The success of scratch detector reaches 81.8%..

DESIGN AND FABRICATION OF BLACKBOARD CLEANER

One of the traditional ways of teaching learning process is carried out by using blackboards in classrooms. Blackboards and chalk are inseperable from classrooms. Thus the dusts from chalk can cause some health hazards when the human inhaled it over a long period of time. Hence an attempt has been made by introducing black board cleaner which is operated by six bar mechanism. Its working is similar to the wipers in automobiles. It reduces the potential work of the person who erase the board and reduces the time consumption in cleaning the blackboard. It also prevent the exposure of chalk dust to atmospheric air and helps to create a dust free classrooms.

Canaries at the Climbing Wall: A Comparative Study of Particulate Matter at Two University Climbing Walls

Magnesium alba—chalk—is regularly applied by indoor and outdoor climbers to their hands to reduce sweat while climbing in order to grip climbing holds. We investigated the potential for suspended chalk dust to lead to unhealthy levels of indoor particulate matter (PM2.5 and PM10) in two university climbing facilities. Low-cost, Dylos DC 1700 PM monitors sampled air quality during two, 5-day sampling periods. Findings revealed “good” PM values at one university climbing facility and “unhealthy” (PM2.5) or “very unhealthy” (PM10) values at the other institution’s climbing wall. Facility predicted over 60% of the variance in PM readings, and post hoc tests revealed 75% of the variance in PM values at the second institution can be explained by open climbing hours. These findings hold a variety of implications for future research and management of university climbing wall facilities to ensure the health of staff and their patrons.