AlphaSheeppig

I tried explaining my work in fluid mechanics (a very little understood section involving the complicated reflection patterns of highly unsteady and non-linear shock waves in supersonic flow) to a few of my friends (a journalist, a fashion designer and a fine arts major) and I think I got pretty far. Given several days, I think I'd have no problem explaining it all to my grandmother (if she was alive), but not to the point that she understood the maths behind it. I think the same goes for most fields in physics... The physical principles can be explained, given some time, but explaining the math behind it all would require your grandmother to go get her PhD herself...

This is exactly the solution my girlfriend and I settled on for this problem. Cow for a female, cattle for a group of females, moo-moo for an unidentified gender, moo-moos for a mixed group.

But put it on ice and the sphere will roll on the spot and the truck will stay still inside. The ball rolls forward because friction between it and the ground (an EXTERNAL force) prevents it from just sliding on the spot. But, that said, this inertial propulsion principle does work. I doubt that it's that efficient, but jet engines are extremely inefficient means of propulsion, so 20 times more efficient is not impossible... And can someone please tell me which laws of physics it disobeys? Because as far as I can see, it uses a power supply and electric motor, so conservation of energy is obeyed, and the forward momentum it gets comes from the loss in momentum from the changing radius of rotation (and thus varying radial velocities) for the weights, so conservation of momentum is also obeyed. Anyone who thinks inertial motion is impossible should go read up on why helicopters need rotors on their tails.

You don't even use F=ma in this problem... It depends on the scale. Measure the height of the scale with nothing on, then measure the height of the scale with the ten pound bowling ball. Call the difference in height in ft x. The spring constant k is then (10 lb/x). Then calculate the total kinetic energy the ball will have when it hits. This is E=mgh where m is the mass in pounds, h is the height in ft, and g is your gravitational constant (32.2 ft/s/s). The distance the scale will "bounce" through is d = sqrt(2E/k), and the force you read off is then F=kd.

That is only assuming a rigid body, but in this case it is true. Without friction, the sphere would merely rotate on the spot and the truck would go nowhere. But there are cases where friction is not necessary for motion. Didn't you ever sit in a cardboard box and move around by throwing your weight forward when you were a kid?

Easily best beginner textbook on Fluid Mechanics that I know of is Munson, Young and Okiishi (http://books.google.com/books?id=bv_uAAAAMAAJ&q=munson+young+okiishi&dq=munson+young+okiishi&hl=en&ei=RJspTKWhI-LbsAbo28HEBA&sa=X&oi=book_result&ct=result&resnum=2&ved=0CDIQ6AEwAQ)... . Also Moran and Shapiro (http://books.google.com/books?id=cN4eAQAAIAAJ&q=fundamentals+of+engineering+thermodynamics&dq=fundamentals+of+engineering+thermodynamics&hl=en&ei=GpspTK_uHcWlsQaAj73EBA&sa=X&oi=book_result&ct=result&resnum=2&ved=0CCoQ6AEwAQ) has a couple of really good chapters on heat transfer.

Sisyphus has the right idea. The odds of winning twice are 5.4 trillion:1, but this assumes that you have not yet won. After the first game, your odds are 2.3 million:1, as the outcome of the first game has no affect on the second. The reason the odds change is that before you win the first game, the odds of winning it are 2.3 million:1, but after you have won it, it is a certainty (i.e. 1:1) since it has already happened.

Hi, I don't see any point in giving my name since you can see it right there... Anyway, I'm an engineering postgrad student doing research into shock wave behaviour for applications to blast waves and supersonic aerodynamics, but I'm interested in pretty much everything...