It's not quite accurate to say there are only four methods for separating a mechanical mixture. There are many, and the best method depends on the specific mixture. However, here are four common and widely applicable techniques:

1. Filtration: This is used to separate a solid from a liquid using a filter. The solid particles are trapped by the filter, while the liquid passes through. Examples: separating sand from water, making coffee.

2. Evaporation: This separates a dissolved solid from a liquid by heating the mixture. The liquid evaporates, leaving the solid behind. Examples: obtaining salt from seawater, drying clothes.

3. Decantation: This separates a liquid from a heavier solid by carefully pouring the liquid off. This works when the solid settles to the bottom of the container. Examples: separating sand from water, decanting wine.

4. Magnetic Separation: This method separates magnetic materials from non-magnetic materials using a magnet. Examples: separating iron filings from sand, recycling magnets from scrap metal.

Important note: These are just four common methods. Other techniques include:

* Sieving: Separating particles of different sizes using a sieve.

* Distillation: Separating liquids with different boiling points.

* Chromatography: Separating components of a mixture based on their different affinities for a stationary and mobile phase.

The best method for separating a mechanical mixture depends on the specific properties of the components.