I need someone to enlighten me; my puny mind is unable to grasp physics.
Say someone is running down a street holding a ball, and he throws it straight up. Does the ball go forward in a projectile motion, or does it go straight up?
I KNEW the answer before, like a long time ago, and now I can’t seem to understand or visualise the motion of the ball.
And, since we’re at it, can someone also tell me how in the world can a ball dropped from an accelerating hot air balloon move UPWARDS?
And also, can someone explain to me why voltage in a parallel circuit splits according to resistance of each path, and why current splits in a series and not in parallel arrangement?
Blah, I feel dumb.
Since the ball has the same forward velocity as the thrower, neglecting air resistance, the ball will continue to move forward at the same speed as the thrower (as long as he is not accelerating in the forward or backward direction).
If you drop a ball from a hot air balloon, it will have momentum due to it’s velocity. If the balloon was rising, it will continue to rise but will decellerate due to the force of gravity until it stops, then it will fall and accellerate towards earth (unless the balloon was rising at or above the escape velocity, in which case it will never return to earth). If the balloon is descending (I’m assuming a slow constant velocity descent), the ball will accelerate towards earth at a rate g. Neglecting air resistance, it will continue to accelerate until it hits something solid.
The first two questions are about relative velocities. When you throw the ball, it might look like you throw it straight up from your point of you, but it’s really also travelling forwards at the same speed as you are running, so it follows a parabolic path, like projectile motion. This is what someone standing still would see.
The second case is similar. When you let go of the ball, it’s still travelling upward at the same speed that you were travelling when you let it go. It takes a while for gravity to slow the ball and make it fall to the ground, so the ball would be seen by an observer in a stationary baloon to go upwards before falling.
Imagine a water pipe at the top of a hill. It splits into two at some point, with one of the pipes being much narrower than the other (the higher resistance). Most of the water will flow through the broader pipe as there’s less resistance, but just before the water enters either diversion, they’re at the same potential (but it’s gravitational rather than electrical). At the bottom, the waters converge again, at the same potential.
It’s not a great analogy (and I no expert) but night help.
It won’t stand up to stern scientific evaluation I suspect:)
Ok i kind of understand it now… but what about the last question? The splitting of current in a series arrangement? Why is it that current does not split when in parallel arrangement but in series?
And really, the idea of a ball falling upwards never ceases to amaze me…
It’s not current that splits in a series arrangement. It’s voltage. Current splits in a parallel arrangement, like the water did in Andy’s example.
Water is always flowing through the pipe at the same speed, and the rate that water comes out of the pipe is equal to the rate that it goes in. So, in this example, the current is the same anywhere in the pipe.
The voltage, however, is the distance the water falls as it goes down each section of the pipe. A pipe that drops 5m could be split into two sections that drop 1m and one that drops 3m. The total voltagge is the sum of all the voltages of each section of wire.
Anyone care to take it from there while I try to reword this so people can understand it?
OK, I’ve had a think about the electrical ones, and there’s a little thought experiment you can do.
For the series example, imagine there are two resistors in series, connected by perfectly conducting wires. The potential before both resistors is +V, the potential at the other end zero. Increase the resistance of one resistor enormously…what happens? The resistance of the first becomes insignificant and all the potential is dropped across the second, but the same current must flow through each.
For the parallel circuit, do the same thing and increase the resistance of one hugely. All the current flows through the other resistor. But, the bit of wire (how technical) which connects the highly resistant resistor at the +V end is connected to the terminal of the +V end of the low resistor, so it must be at the same potential.
Clear as mud?
That’s my ignorance fighting over for the day, my head hurts;)
monny, you may not need it, but for the benefit of others who might read this post, here are a couple of basic physics books that are accessible to an average reader with an interest in the subject:
“Understanding Physics” by Isaac Asimov - a bit dated, but it reads well and provides a good level of descriptive detail without using a lot of mathematics which tends to drive people away.
“Six Easy Pieces” by Richard P. Feynman - an introduction to 6 core concepts of physics written for a non-technical audience. includes topics on Conservation of Energy, Gravitation, and Quantum Mechanics
“Six Not-So-Easy Pieces” by Richard P. Feynman - six more advanced concepts of physics including Relativity, Symmetry, and Space-Time. Again, written for general audiences.
After reading and understanding them, you shouldn’t have any problems answering the types of questions monny posted or engaging in intelligent conversation on most topics in physics.
