prompter: Which kind of tree produces the hardest wood?

assistant: The hardness of wood can be measured by the "Janka hardness test" developed by Gabriel Janka.
The highest value measured currently is the Australian "Allocasuarina luehmannii" (also called buloke or bull-oak).

prompter: Oh wow, that is super interesting! Can you still use a normal axe to chop this wood? Or does it even break a chainsaw?

assistant: Wood with an exceptionally high Janka hardness, like the Allocasuarina luehmannii, can be very difficult to cut and chop with standard tools. Some key points:

It would require a very sharp axe and a lot of force/effort to chop through this wood with an axe. A dull axe would likely just bounce off or get stuck.
It can dull chainsaw blades quickly and may require a more powerful chainsaw.
It can be hard on power tools in general and shorten the lifespan of cutting discs, blades, etc.
It may require pre-drilling and screwing/bolting instead of nailing due to how hard it is.

So while you can cut it with the right tools and blades, it does present more challenges than typical softer woods. The extreme hardness is what makes it durable for uses like flooring or construction, but that same hardness makes it much more difficult to work with manually or with standard tools.

assistant: Is should be still possible to chop this type of wood with an axe, or chainsaw, but it will be much harder and time consuming, according to "Janka hardness test" you would need 25,000 newtons to embed an 11.28-millimeter-diameter steel ball halfway into the wood.

assistant: There are several trees that produce very hard wood and it can be difficult to determine which one produces the hardest wood. However, one of the hardest and densest woods in the world is produced by the Lignum vitae tree, which is native to the Caribbean and the northern coast of South America.

Lignum vitae wood is exceptionally hard, heavy and durable, making it ideal for use in applications that require resistance to wear and tear, such as shipbuilding, bearings and tool handles. It is so dense that it sinks in water and has a Janka hardness of 4,390 lbf (pounds-force), one of the highest of any tree species.

It's worth noting that the hardness of wood can vary depending on factors such as the age of the tree, the growing conditions and the part of the tree the wood comes from. In addition, different sources may have slightly different rankings of wood hardness based on their testing methods and criteria.

prompter: How can that wood be used in shipbuilding if it's so dense that it sinks in water?

assistant: The density of the building material itself is not a crucial factor; for example, many ships are built of even denser steel.  The critical factor in ensuring a boat will float the displacing a mass of water greater than its total weight.  Typically a ship's hull surrounds a volume of air, so its average density is much lower than the water it is floating in.

assistant: You're right that Lignum vitae's extreme density causes it to sink in water. However, its density and hardness also make it very resilient to impact, wear, and crushing forces. In shipbuilding, Lignum vitae is often used for applications where these properties are important, such as:

- Propeller bushings and bearings: Lignum vitae's hardness and lubricity make it good for bushings and bearings that support rotating shafts. It withstands the friction and forces involved well.
- Pulley systems: Lignum vitae can be used for sheaves and other pulley system components that need to withstand tension and wear.
- Ship's wheels: Lignum vitae's density and hardness make it a good material for ship's wheels and other steering/control components that need to withstand forces.

So while Lignum vitae sinks in water due to its density, that same density is what makes it useful for certain high-stress, high-impact components in shipbuilding. It is often used for core parts that are then covered or combined with other materials.

assistant: Altough the wood is dense, the water still applies an upwards force to it. 
A boat can float on water because the surface in contact with the boat in an upward direction provides enough force to stop it from sinking. To achieve this effect, the boat does not have a flat bottom but a sloping one. The deeper the ramp goes into the water, the more force the water exerts to keep the boat afloat. The surface of the ramp allows for more water to contact the boat to create that upwards force.

In short: the slope angle is more important than the material used to build the boat, to keep it afloat.

assistant: Brazilian Walnut (Ipe) - This tree, which is native to South America, produces one of the hardest woods in the world. It is often used for outdoor decking, furniture, and flooring.

prompter: what's 3 + 3 ?