Why do the wings on a Boeing 737 point upwards at the ends?

A winglet is a device used to improve the efficiency of aircraft by lowering the lift-induced drag caused by wingtip vortices. The winglet is a vertical or angled extension at the tips of each wing.

Winglets work by increasing the effective aspect ratio of a wing without adding greatly to the structural stress and hence necessary weight of its structure — an extension of wing span would also permit lowering of induced drag, though it would cause parasitic drag and would require boosting the strength of the wing and hence its weight — there would come a point at which no overall useful saving would be made. A winglet helps to solve this by effectively increasing the aspect ratio without adding to the span.

The exact upward angle (called cant) of the winglet, and its inward angle (or toe) is critical for correct performance, and is determined for each aircraft application. The vortex which rotates around from below the wing strikes the angled surface of the winglet, generating a small lift force that angles forwards relative to the direction of flight — thus the energy in the vortex contributes to thrust rather than drag as it normally would. This is analogous to a sailing boat sailing very close to the wind. This small contribution can be very worthwhile on long-distance flights.
To prevent cortex from diminishing lift.
Its all to do with the air flowing over them correctly I think. As long as they are pointing up dont worry!
They are called winglets and it is suppose to help the airplane be more fuel efficient. Southwest's 737-700 I think has them and a few other carriers use them also.
So when it crashes that bits survives, it's where they keep the black box!

Seriously I suppose it's to do with aerodynamic in which case, sorry not a clue!
William T had it almost correct.
They are called Winglets.
They are to eliminate the vortex at the wing tips.
Reducing or eliminating the vortex increases stability giving a better ride. And also increases fuel efficiency.
'Cow Horns' - I think is the nickname for them, they help the plane with aerodynamics by cutting out the drag (of air) which comes at the end of the wingtips.

On film you can best see the effects of not having them when lanes come into land either in mist of when it is raining .there are 'swirlings' (a 'vortex' at the end of each wing) of these substances seen - which can be a hazard to a planes' stability on landing (partly as a result to local terrain).

I also believe they help in cutting fuel costs, for pretty much the same 'drag' reasons.

I know a little, not a lot about aviation.

So when you look out of the window and they are pointing down...S. :-) :-)
at the tips of a wing, the air flow currents have the tendency to move from below to on top of the wing, generating a balance of the air pressure from upper surface with that from the lower surface,and that's exactly what shouldn't happen; this difference of the air pressure generates the lift force and those upper wing tips avoid this loses of aerodynamic lift force and some other undesired phenomena generated by the improper flow of the air string as the butterfly effect.
This is all about directing airflow. The wing tips point up at the ends (commonly known as winglets), to direct more airflow over the trailing edge (rear) of the wing. This helps to generate lift more efficiently. Without these, air flows off the wing tips which creates vortexes which increase drag.
There winglets disigned to improve drag.
There called wiinglets and make the plane econimise with fuel.
I think
my dad worked for both Lockheed and General Dynamics.
the easy answer is: to hold and force the air over the wing and create more lift rather than that air slipping off of the wing tip to be lost or wasted. i cannot tell you the name of the devise at the end but I'm sure a web search could tell you. I think you might see more of these in the future as we learn more of the properties of both air and flight. the vertical "tip" allows for a more average wing to do the same work of a larger wing, instead of having to engineer and build (at a greater cost) a larger wing ,as aircraft grow ever larger.
The upwards pointing thingy is called winglet.. not getting into advanced aerodynamic explaination (good for u to get it:) )
As a general phenomenon the aircraft wings gain lift coz of the air pressure diffrences on the top and the bottom surface of the wing (ie low pressure on the top and high pressure on the bottom) the shape of the wing is made in such a crossection to facilitate this.. it is called AEROFOIL crossection
now what happens is like v know that air tends to move from high pressure zone to low pressure zone.. ie, it tries to balance the pressure on both the top and bottom surfaces. BUT if both the pressures would be equal there would be no LIFT possible at all.. so to prevent the air from escaping from the bottom surface to the top surface (ie, high pressure to low pressure) the winglets are installed.. they act as a barrier to the airflow trying to escape

there's an intresting question relating to this. it goes like.
how much weight does a 6ft high winglet add to the Boeing 777 airplane
the answer is : NONE !
explaination. it is because the lift capacity of the airplane drastically increases after the installation of a winglet on the wing and the winglet also serves as a fuel reservoir to store upto 700 lts. of fuel !
They are called winglets.

They REDUCE the vortecies coming off the tip of the wing. Vortices are required for lift prodution and if you put a big enough winglet to eliminate them, you would eliminate lift.

All they do is increase the effective span of the wing without increasing the actual span. They are no different than having an increased span wing. (like the 777).

Winglets add considerable weight because the wing has to be strengthened and a huge weight has to be installed at the front of the winglet to prevent it from increasing the angle of the wing, plus the weight of the winglet itself.

Winglets only reduce drag at high altitudes and low airspeeds where induced drag (due to vortices) is predominant. The fuel savings is almost unnoticable.
They are winglets, and reduce drag on the aircraft.

They do this by 'interfering' with the vortices which develop along the leading edge of the wing (and which roll backwards) along to the end of the wing and then to the rear, so you have two rolling vortices turning inwards at the rear of the aircraft ( seen that at an airshow when someone does a sharp pullup - especially high performance jets?)

The winglets moidify this airflow to reduce the drag, so the aircraft uses less fuel, has better performance - and so keeps your fare down!!
To stop vortices from developing at the wingtips. This reduces drag which decrease fuel consumption
the winglets are there to reduce the induced drag and improve the efficiency of the plane.
To prevent Vortexes.

A wing creates lift by creating a lower air pressure over the wing than the pressure under the wing (by making the air move faster over a curve). This difference in pressure causes lift, as the higher pressure wants to get to the lower pressure and equalise it. At the wingtips, the high pressure air can slip around the wingtip and mix with the lower pressure air, creating an air swirl or vortex. this increases the aircraft's drag and hence reduces the aircraft's efficiency, needing more fuel to get to it's destination. Bending the wingtips greatly reduces the ability of the air to form vortexes.
Because the pilots keep hitting the hangar with the wings when they put the plane to bed at night and they've bent them out of shape.
They're called wingets or wingtips, they're to increase efficiency, but not all 737s have them

Experts are undecided how much fuel is saved, and whether it's worth having wingtips on all aircraft