$(2$ marks$)$ Ball$-$bearings are by far the most common type of bearing used. What types of loadings must we consider for the proper use of these types of bearings?

$(1$ mark$)$ The figure shows an example of what type of bearing?

$(2$ marks$)$ Mechanical systems by definition have moving parts that allow for work to be performed in an efficient way. Many mechanisms have metal$-$on$-$metal components. In what ways can lubrication be used to protect these mechanical systems?