Van der Waals forces are even weaker than Hydrogen Bonds which are much weaker than Covalent Bonds.  However Hydrogen Bonds - and even Van der Waals forces - can be quite strong if the atomic distances are small.
 
 
 

Examples:

In fact ........if the surface of the metal block and the surface of the car roof had been highly polished - so they would fit together at close atomic distances - the H bonds in a film of water would have been strong enough to lift the car by themselves.

If H bonds in 1 square foot are strong enough to lift a car, consider how strongly they can hold atoms and molecules together !!!!!
 
 
 

Van der Waals Forces.

Geckos, or house lizards, are able to run up walls and across ceilings as easily as across floors.  They can even dangle effortlessly from a ceiling by just one toe.  The mechanism by which they are able to do this has never been clear:

• It used to be thought that perhaps Geckos had sticky foot pads - however close examination revealed there was no "stickiness" at all on a Gecko foot.

• Another hypothesis was that there was some kind of "suction cup" mechanism.  However suction cups work by squeezing out all the air underneath the cup, so that atmospheric pressure will press down so strongly on the cup that it adheres to a smooth surface.  Obviously suction cups will not work in a vacuum because if there is no air there is no air pressure to press the cup onto the surface.  However  Gecko feet still "stick" even in a vacuum!

• Scientists and Engineers at the University of California Berkeley now have evidence that it is Van der Waals Forces which stick Geckos to the ceiling!

Microscopy has shown that a gecko's foot has nearly five hundred thousand hairs or setae.  These are made of the protein keratin as are mammalian hairs and bird feathers.  However these hairs are very small -  each 130 µm long seta is only one-tenth the diameter of a human hair and the length is less than the diameter of this period  ----> ^.

As small as it is however single seta contains hundreds of projections, each one terminating in a cluster of four 0.5 µm disk-shaped spatulae.  These spatulae are too small to be seen with an optical microscope ( a bacterium is ~ 1 µM in size).  It is estimated that a Gecko has approximately 1,000,000,000 spatulae on its four feet.

It appears that the spatulae form such intimate contact with surfaces that very small atomic distances allow Van der Waals forces to act.  The sum of these weak forces, acting on a billion spatulae on 2 million hairs, is powerful enough to do far more than simply stick a Gecko to ceilings.

• The scientists showed that a single seta could lift an ant.

• A million setae (only half those on a Gecko!) covering an area the size of a small coin could lift a child weighing about 45 pounds!

So how does a Gecko get itself unstuck when it is running?  It turns out that the setae only contact the surface closely enough for Van der Waals forces to act when they are in a particular orientation.  If the orientation is changed the distances become too great for Van der Waals attractions, and the seta lifts easily.  Geckos have a peculiar behavior of toe uncurling and peeling in which the setae are rolled onto a surface, and then peeled off again as the animal lifts its foot.

It is hoped that this natural mechanism can be mimicked to produce reusable "gecko tape".  Rock climbers have already expressed enthusiasm for "gecko gloves" but these are considered unlikely!
 

Their findings are reported in the June 8, 2000 issue of Nature.