Quote:
Originally Posted by Tcoat
It is basic physics. I thought engineers understood such but guess I was wrong.
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in case you aren't just trolling I'll try to explain briefly.
In rolling motion, you have two types of velocity, translational and angular. Angular is always perpendicular to the radius, while translational is a constant in the direction of travel. To get the velocity of any point on the wheel, you add both of these velocities together.
First, break down the angular velocity into it's horizontal and vertical components. This is typically done through basic trigonometry, but to spare you the math we will look at 4 easy points to visualize. At the bottom of the wheel is as negative (backwards) as it is going to get. At this point all of the angular velocity is horizontal. At the top of the wheel it is as positive (forwards) as it is going to get, again the velocity is 100% horizontal. At the front and the back (relative to the car) of the wheel, the horizontal velocity is 0, meaning those points are traveling vertically. Don't believe me? Have someone swing a weight on a string and watch it from the side.
Knowing that, the best chance for a rock to be flung straight back is if it were flung from the bottom of the wheel right? However, we know that the bottom of the wheel, in contact with the ground, has to be moving at the same speed as the ground, otherwise it would be slipping. Which means that the bottom of the wheel must be moving at a horizontal velocity of 0kph.
As discussed before, the bottom of the wheel is the most negative angular velocity you can have. So if the point of the wheel with the most negative angular velocity is traveling at an total (angular+translational) velocity of 0, then all other points on that wheel must have a positive total velocity.
Therefore something which at one point matches the actual velocity of the wheel and is then thrown off can only be going forward or remain stationary.