why does th canvas roof of a convertible car bulge upward when the car travels at high speeds???
363865
As the car moves along, air passes over the top of the roof, creating an area of low pressure.  The air pressure inside the car, having a higher pressure than outside, then forces the canvas upward.\n\nThe principle is similar to that of an airplane wing.  Of course though, there isn't anywhere enough lift generated to make the car fly.
906102
If an aircraft window was square or rectangular (as the used to be) there is a concentrated stress on the corners of the window.\n\nThis stress, due to stresses on the aircraft as well as pressures, has previously caused windows to blow out.\n\nA circular window will spread the forces evenly around the frame, reducing the stresses on the seam of the window.
491260
It's a large amount of air pushing through a small space. It's not the "buns" flapping. It happens at the point of exit. \n\nThere really isnt any more delicate way to put it.\n\nI cant believe I just answered this question. I need a life!
611973
*******************************************************\n*It's not a paradox to begin w/!!!!  It's perspective.*\n*******************************************************\n\nThe question is "immovable object & irresistable force." It's a perspective thing. They do exist. The problem lies in the fact you're on the outside looking in on the system. \n\nWhat is the irresistable force? There IS only one. Gravity.\n\nWhat is your immovable object? Pick something. Anything.\n\nNow drop it. From your perspective the object falls to the ground. BUT what happens from the object's perspective? The ground jumps up and hits it, while the object remained still. It's your basic car window perspective question.\n\nIf using large enough objects, it can become a "matter shake."
1168063
Air pressure.  It actually implodes not explodes.  There is no airpressure in the cargo holds at that height.  The key being that it was sealed.  Watch for shampoo bottles or anything like that.  I had a suitcase full of shampoo. :-(
981896
The upward reaction force (at the top of the bump) is NOT mg + mv^2/r.\n\nPer unit mass, it is g - v^2/r. Note the sign.\n\nAlso, the relevant mass is not the whole mass of the car m but, say, about *half* of it---the rear wheels are not even in contact with the bump unless it's a really huge one (was this overlooked when the question was set?)\n\nThe previous answers are *almost* correct---except for the sign mistake (+ instead of - in the centripetal term). Taking the upward direction as +ve, the gravity force is -ve (-g per unit mass), the bump's reaction n is +ve, and the centripetal force is -ve (c = -v^2/r per unit mass), with c = -g + n (gravity and reaction add up to provide the req'd centripetal acceleration, which is negative, i.e. downward). So, per unit mass, the reaction is \n\nn = -gravity + centripetal = g - v^2/r.\n\nIOW, at that point, the bump's curvature actually lessens the load on the wheels (it's a different story at the point of initial contact of course). \n\nThe relevant mass for the front wheels is m/2, so the numerical answer is:\n\nReaction on the *front* wheels is \n(g - v^2/r)m/2 = (9.8 - (16.6)^2/42.1)1720/2\n= 2800 (newtons) = 286 kG (kilograms-force)\n\n[An answer that forgets to halve the mass would be 5600 N.]\n\nReaction on the *rear* wheels is: gm/2 = 9.8*1720/2 = 8428 (newtons) = 860 kG (kilograms-force)\n\n\nPS: I see now that the correct sign did also occur to gp4rts in his last edit.
937731
Because the faster a vehicle goes, the greater the momentum.\n\nMomentum = mass * velocity, so it increases with velocity.\n\nWhen you get in an accident, and if your car is brought to a sudden stop, you still have this momentum, this velocity. If you are not strapped down, then your movement, at the velocity continues, regardless of the new post-accident velocity of the car. If it is stopped then you will impact the instrument panel and windshield with the same velocity and momentum you had.\n\nIf you have an accident without a seatbelt, without airbags, you will get seriously messed up. And the faster you are going, the worse off you'll be.
587814
The rear window of a car is made of tempered glass -- the glass is heated approximately to its softening temperature and then cooled abruptly to put its surface under compression, leaving its inside material under tension. That tempering process makes the glass extremely strong because its compressed surface is hard to tear. But once a tear does manage to propagate through the compressed surface layer into the tense heart of the glass, the entire window shreds itself in a process called dicing fracture -- it tears itself into countless little cubes.\n\nThe stresses frozen into the tempered glass affect its polarizability and give it strange characteristics when exposed to the electromagnetic fields in light. This stressed glass tends to rotate polarizations of the light passing through it. As a result, you see odd reflections of the sky (skylight is polarized to some extent). Those polarization effects become immediately apparent when you wear polarizing sunglasses.
28916
That's just the nature of the optics. They need to be bent in order to have you - from the front seat - see a wide enough area along the side of the car. The result is a curved lenses and distortion.
48985
airplane wings work because of their curvature - the upper surface of the wing is more curved than the lower surface, so air moving over the top of the wing has to take a longer path.  \n\nthis longer path causes the air to thin out over the top surface of the wing, and this leads to a lower pressure on the top surface.  the higher-pressure air on the underside of the wing pushes the wing upwards into the lower-pressure region, just like the higher pressure inside a balloon pushes the balloon outwards into the lower-pressure atmosphere.\n\nanyway, i think you can think about a leaf on a windshield as acting like a wing of sorts.  air will flow faster over the upper surface of the leaf but stay trapped underneath.  if the leaf is solid, then the pressure differential pushes outward on the leaf, away from the windshield.  \n\non the other hand, if there is a slit in the leaf, then the higher-pressure air underneath can move through the slit and equalize the pressures, so there is less force on the leaf pushing it away from the windshield.\n\nas for holes, perhaps if the holes were big enough, you would no longer have the smooth ("laminar") flow over the surface, and instead get turbulent air that causes a vortex to form.  \n\nvortices are lower pressure areas so that might suck the leaf off.  or, a big hole might cause an edge of the leaf to flip up into the airstream and catch some of the air, forcing it down under the leaf and pushing it off the windshield - whereas a slit might still allow the air to flow smoothly over the leaf yet still equalize the pressure.\n\ni'm totally guessing, but i guess it's a reasonable theory.
176123
The force that pulls you towards the side of your car when you go around a corner too fast is actually inertia.  It's the same force that makes you fly forward when you hit the brakes too fast or sink into your seat when you lay on the gas.  According to Newton (I believe it's his third law), "an object in motion tends to stay in motion and an object at rest tends to stay at rest."  Well when you are in your car and you are moving in a straight line, your tendency is to keep moving in that straight line.  When you take the turn too sharply, the car is turning but your body's natural tendency is to keep moving in that straight line, so you get pushed up against the side of the car.  The same justification explains why you move forward or back when the car accelerates or decelerates too quickly.\n\nCoriolis force is a completely different force that is caused by the rotation of a sphere and the fact that the sphere is densest in the middle, with decreasing density as you approach the poles.  This change in density causes a force which makes moving things tend to move towards the equator of the sphere.
923574
It goes into thermal energy (heat) as the brakes heat up due to friction and perhaps to other, less significant sources of energy loss (e.g. sound of brakes squealing).\n\nNote: The car doesn't really gain energy, it just converts its gravitational potential energy (from being at the top of the hill) into kinetic energy (the energy associated with motion).
611670
It doesn't make the car faster; it decreases the frictional force that is slowing the car down.\n\nAn object has to move the air out of it's way for it to pass through.  Buses, for example, have a big, flat front end that sorta traps air in front.  You really want to cut through the air, like a sports car.  Also, the air flowing over the body can create drag.  Hence, a nice smooth surface with little variation is good.  Finally, the back side of a car makes a difference.  Again, the bus will create a low pressure area as air has to fill the space that it leaves.  This is bad.  It's much better to slowly close the space behind the vehicle.
1046019
when a car speeds by you, you feel wind. it's the same way with the earth, as it spins very fast.
635462
Maybe the car designers like a bottom heavy babe! In fact CG or centre of gravity of the vehicles is at a low point if the heaviest weight is aaranged at the lowest point. Since engine is the heaviest part, it is placed at the lowest possible point to give car highest stability
990419
To look like it is flying.
501575
the dimpling creates an aerodynamic effect that allows them to stay aloft longer.  \n\ninterestingly, the same effect occurs on the Mig29.  although, there it is an accident.  poor manufacture, not design causes the dimpling.