If u ride in a car and throw a stone up and down, why doesn`t it go backwards?
445486
Because the up/down motion is independent of the side-side motion. The stone is already going at whatever speed the car is and that doesn't change. The only thing that changes is the up/down part of the motion. For someone outside the car, the stone looks like it goes along a parabolic arc, not just up and down.\n\nThis is related to the relativity of motion. If you are moving uniformly, it is impossible to tell whether you are moving or not unless you look outside the car.
338364
Wagon wheel effect read about it at http://en.wikipedia.org/wiki/Reverse_rotation_effect
234240
Because if it went counterclockwise time would be going in reverse? :)
512623
I will state this here, in yet another question: THERE IS NO SUCH THING AS CENTRFUGAL FORCE!! Look it up in a basic physics textbook like Giancoli or Serway. Or even do a google search. You have to understand what reference frame you're talking about. The fact that your body tends to want to move to the outside of the curve when your car goes around in a circle has nothing to do with anything other than the fact that your body wants to keep going along in a straight line (conservation of momentum), but the car gets in front of it at every turn (semi pun intended). What is actually happening is that the car is an accelerating reference frame.\n\nAs for the moon/earth question... imagine a man 6' tall throws a tennis ball horizonatally with respect to the earth's surface. The ball will go forward a certain distance (because of it's velocity tangential to the earth's surface) as it falls the ~6' to the ground (because gravity pulls it down). The faster he throws the ball (horizontally), the further it will go before it hits the ground. If he throws it fast enough then the amount that the ball travels forward and the amount that it drops towards the earth's surface can match the curvature of the earth, and the ball will orbit the planet (neglecting air resistance, as we physicists always do) and come around and bonk the thrower in the back of the head. The moon is just a much larger tennis ball, thrown by a much larger man.\n\nYour eqn. is correct, but it only describes the force acting upon the moon. It is not the equation of motion, which detirmines what actually happens to the moon. The equation of motion is:\n\nF = m * a  (F = force, m = mass of moon, a = acceleration of moon around earth)\n\nIn the case of the circular motion of the moon around the earth, "a" is defined by:\n\na = (v^2)/r (where v is the magnitude of the velocity of the moon and r is the center-to-center distance from the earth to the moon)\n\nPlugging one into the other you get:\n\nG * M * m/r^2 = m * (v^2)/r (where M is the earth's mass)\n--> G * M/r = v^2\n\nSo, as long as the tangential velocity, v = sqrt(G * M/r), the moon falls just enough towards the earth as it travels just enough tangentially second by second, that it continues to orbit around the earth. (Note: there is NO CENTRIFUGAL FORCE anywhere in any of these eqns.!!)
886324
Think of it like this, if you have a car on ice, there is no friction. The wheels will spin, but the car won't go anywhere. If you have a car on pavement, the wheels spin and the car moves. This is  because the friction where the wheel is touching the pavement doesn't move. Instead,the wheel to rotates and the next part of the wheel touches the pavement and 'doesn't move'.\n\nHope that makes sense. I was never all that good with physics.
1176333
The fly floats in the air. The air in a moving car more are less travel with the same speed. The fly floating in air inside car does not hit on the sides of the car. While travelling in open lorry, if you throw a ball vertically in the air, the ball reaches your hand again, even the lorry moves. This is because, the ball also got the momentum to travel along the lorry while it is in the air. The will work out for certain heights only.
240419
It should flow counterclockwise because of the Coriolis effect.\n\nHowever:\n\n>> But, the Coriolis force is very small, indeed. \n \nCompared to the rotations that one usually sees (tires on a travelling automobile, a compact disc playing music, or a draining sink), the rotation of the Earth is very small: only one rotation per day. The water in a sink might make a rotation in a few seconds and so have a rotation rate ten thousand times higher than that of the Earth. It should not be surprising, therefore, to learn that the Coriolis force is orders of magnitude smaller than any of the forces involved in these everyday spinning things. The Coriolis force is so small, that it plays no role in determining the direction of rotation of a draining sink anymore than it does the direction of a spinning CD. \n\nThe direction of rotation of a draining sink is determined by the way it was filled, or by vortices introduced while washing. The magnitude of these rotations may be small, but they are nevertheless gargantuan by comparison to the rotation of the Earth. I decided to include a picture of a draining sink, and the first one I tried in my house was found to drain clockwise (the opposite of what the silly assertions would have it do here in the northern hemisphere). This direction was determined entirely by the way the tap filled the sink. The direction of rotation of a draining toilet is determined by the way the water just under the rim is squirted into the bowl when it is flushed.<<\n\nI guess you'll just have to observe - I have made the water in kitchen sinks swirl the "wrong" way just for the heck of it, and it doesn't begin to immediately go the "right" way unless I act on it.
1183225
The instant an object is released as it is thrown upwards, it begins to accelerate downward.  This downward acceleration is caused by gravity (the force of weight, m*g, acting downward on the object).  Although the object may continue to travel upwards for a brief time, it is continually slowing in the upward direction as it accelerates towards the ground.\n\nObjects "fall" towards the ground (in the direction of the center of the Earth's mass) since that is the direction of the force of gravity is exerted on them.  An object cannot "fall" up since there is no net force acting in that direction.
863216
It has to do more with the material of the ground rather than with the surface. It all depends on it's elastic coeficient. The least elastic, the more it will bounce because of the transmission of the kinetic energy.
682473
Cars are aerodynamic to reduce wind resistance but this does not create the Bernoulli effect necessarily.\n\nIn fact cars, especially race cars, are designed like upside down aircraft.  Instead of lift, they use the Bernoulli principle to create a down force.\n\nIf cars were round on the bottom and flat on the top then the Bernoulli principle would kick in and create lift.  Probably not enough lift to make the car fly but probably enough lift to make it uncontrollable on the ground.
784055
The way to do this is to first work out the acceleration required to turn the car round the curve.\nFrom there it is a simple matter of working out what angle the road needs to be at so that gravity will provide that acceleration.
904552
Both balls would hit the rocks at the same speed.\nBall #1 would leave your hand travelling straight up at speed 'u'. It travels up, stops, and starts plummeting back to earth. When it reaches the height at which it left your hand, it is travelling at speed 'u' straight down. The speed that it hits the rocks at is u+(time x 10m/s/s).\n\nBall #2 would leave your hand travelling straight down at speed 'u'. The speed that it hits the rocks at is u+(time x 10m/s/s). It is the same speed.
84946
While trying to drive to the store, I accidently put the car in reverse.  I went backwards at an average spped of 5 miles per hour and ended up 500 ft further away from the store than when I started.  How long was I driving backwards?
44366
einstein's theory of relativity.  in the frame of reference of the car, you are stationary, the fly is stationary, and everything else in the car or moving with the car is stationary. this is why if you are in a car and drop a book onto the seat, it goes straight down, not toward the back. it is going at the same speed as the car and therefore is still relative to the car. there is no force acting on it to make it behave otherwise.  that's why you don't feel anything in a car unless you're accelerating or decelerating. so you feel like you're pushed forward when the car is coming to a sudden stop. because then there's a force stopping the car, and therefore you, so you feel it. in this case, the fly would also go flying(no pun intended) to the front of the car.\n\nif this is still unclear, think of the earth. the earth is rotating with a speed of over 1000 m/s, but you don't feel it. that's because you're moving at that same speed, you're stationary relative to the earth so you feel stationary because your frame of reference is the earth.
932837
forces are opposite and equal, otherwise you would change speed/direction.
8313
No, and the Earth won't rotate 'backwards', but if it did, it would be a global disaster. The spin of the earth slightly counteracts gravity, so if the earth stopped and turned around, the tsunamis, earthquakes, and global havoc would be immense.
1065923
each frame (24ish per second) captures the position of the wheel at a specific point in its rotation. alter the speed of the wheel and you alter the capture position of the wheel. the perception on film is of the wheel spinning backwards because the position of the wheel as each frame is captured is at a point just before a complete rotation.\n\nalso strobe lighting effects and spinning wheels can have the same percieved effect