Why Does Chalk Stay on the Blackboard and Why Should You Use It?

Chalk, a traditional tool used in teaching and education, often leaves lasting marks on blackboards. This phenomenon can be attributed to two primary factors: friction and adhesion. Understanding these factors can help educators choose the most appropriate writing medium for their teaching.

Breaking Down the Science: Friction and Adhesion

When chalk is rubbed against the surface of a blackboard, it creates friction. This frictional force helps the chalk particles stick to the board, allowing the marks to remain in place until they are wiped away. Additionally, chalk is made of calcium carbonate, which can form a slight bond with the blackboard's surface. The microscopic texture of the blackboard provides small grooves and pits that can hold the chalk particles, further enhancing its adhesion.

Furthermore, the rubbing between chalk and the board can create electrostatic charges, leading to attractive forces. These forces help the chalk particles stick to the board more effectively. The process of abrading the chalk leads to weak intramolecular attractions within the chalk particles, which in turn allows them to adhere more strongly to the board's surface.

Rubbing Creates Electrostatic Charges

The interaction between chalk and the blackboard surface can result in the creation of and minus charges. This phenomenon is based on the principle of triboelectrification, where friction between dissimilar materials can cause one to gain a positive charge and the other to gain a negative charge. The resulting attractive force between these charges ensures that the chalk particles remain on the board.

Comparison with Whiteboards and Markers

Besides the traditional blackboard, many modern classrooms also use whiteboards and markers. While blackboards require chalk, which can be somewhat dusty, they have their advantages. For instance, chalk lasts a long time and doesn't get stolen, unlike markers which are often quickly used up and can become dry. This can lead to having to carry extra markers or even resorting to stealing them from other rooms.

Using whiteboards and markers comes with its own set of challenges. Whiteboard markers get used up quickly and often dry out, creating a lot of non-organic waste. In addition, the smell from the markers can be unpleasant, and the resultant waste is mostly non-recyclable plastic items. This creates logistical challenges for educators, especially if a room does not have any usable markers.

Advantages of Chalk

One significant advantage of chalk over markers is the ease of determining if you have enough chalk to make it through a class. In classrooms where whiteboards are the primary writing surface, there might be five or six dead markers and only one working one in the room. Chalk, on the other hand, is often easily visible with sufficient amounts, as unused chalk objects are typically not hidden or misplaced in the same way as markers.

Additionally, many teachers prefer to carry their own chalk, especially when using a chalk holder, because the handle provides a more comfortable grip. However, the feel of chalk may not appeal to everyone, making it a subjective choice.

In conclusion, while whiteboards and markers have their benefits, the traditional chalk and blackboard combination continues to be a reliable and versatile tool for educators. Understanding the principles behind how chalk sticks to a blackboard can help in making informed decisions about teaching materials.