Where would be without glue? We use it in some many different ways including PVA glue for all your family craft needs and even as a metal bonding adhesive like you can find at www.ct1ltd.com/product-applications/metal-to-metal-adhesive But have you ever stopped to think how this wonder of science actually works?
There are many different types of adhesives from synthetic made to natural and many of the natural ones have been used for centuries It is thought that early cavemen used a bitumen type material (a bit like tar) to stick the flint axe heads to the top of their hunting spears. These would then have been bound at the bottom by some type of rope to help keep them in place.
Glue uses some of the natural forces that we see in everyday life in order to work. To understand how glue works you need to first know these forces. Gravity is the force that stops us from spinning off into outer space and essentially pins us to the ground but it is a weak force as by using our own muscles we can jump from the ground before being pulled back down again. It is a bit like unsticking ourselves temporarily from the earth. When items stick together there are essentially two different forces at work adhesive forces and cohesive forces.
Adhesive forces are those that make one item stick to another, such as a water drops from a rest downpour sticking to your window. The cohesive forces are what cause the water droplets to occasionally stick to one another. This is of course very simplistic terms. Cohesive forces are stronger than their adhesive counterparts. Theses exact same forces occur with glues and adhesives.
If you were to stick together two pieces of wood, you would have adhesive forces occurring between the glue and each individual piece of wood and cohesive forces occurring within the glue itself. In simple terms this means that the glue has to be strong enough not to simply break apart when you stick together the two items. If you were to use a strong adhesive to glue something to wall, if the adhesive forces we strong then the item would remain stuck to the glue, but if the cohesive forces were weak then the glue would simply break in half causing your item to fall from the wall leaving the other half of the glue still stuck there.