I would think that if, say, you throw a ball against a wall and it ricochets back, the velocity isn't changing instantaneously, just very quickly.  But if you shine a flashlight at a mirror and the light reflects back, is the velocity changing instantaneously or just very quickly?  

I'm not trying to be a smart ass asking the question, I'm really wondering and I can't quite get my mind around it.  

FP

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Very quickly. The light still has a velocity, its velocity is just so large that it changing from 3*10^8km/s or w/e to -3*10^8. Nothing is instantaneous as far as I can think of (so no one comes and rattles out a list of stuff that isnt actually instantaneous, blah blah)

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Again, it is different with light. And all subatomic particles, for that matter. Like electrons.

FP

EDIT: Spelling

Post edited at 2:30 pm on April 2, 2007 by FurryPanther

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LiveWire's resident furry.
I am the God of Unsultry Pleasures. Bow to me!
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Malo periculosam libertatem quam quietum servitium.

Reflected light will have the same velocity either direction but here you are talking about photons not physical mass.

Post edited at 2:35 pm on April 2, 2007 by ZenaGirl

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The velocity of a ball can NOT change INSTANTANEOUSLY.  A high speed camera would show that the ball would be compressing as it hit the wall and would be slowing down during that time.  

Reflected light will have the same velocity (300,000mtrs/sec) either direction but here you are talking about photons not physical mass.

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Alright, I remember learning about things compressing as they collided, but I wanted to clarify...

I still don't understand a lot of things about light, though.  My physics teacher... ugh, I cannot express my hatred for my old physics teacher.  He was terrible.  

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I still don't understand a lot of things about light, though.  My physics teacher... ugh, I cannot express my hatred for my old physics teacher.  He was terrible.  

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Light is a wave, not a mass, so it acts differently, even with it's particle properties.

FP

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LiveWire's resident furry.
I am the God of Unsultry Pleasures. Bow to me!
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Malo periculosam libertatem quam quietum servitium.

If you throw some batteries into a bathtub, could a person in it get shocked?  

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Ok, I have another kinda strange question that has been haunting me for a couple of years:  

If you throw some batteries into a bathtub, could a person in it get shocked?  

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Not with ordinary batteries- the voltage is very low- typically just 1.5 volts per cell.  That compares to 120 volts that comes from a outlet.  Also it's DC voltage which requires higher values to shock than AC voltage (like from a outlet).

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 ~ Anyone who is not confused doesn't understand the situation ~

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Quote: from palepalepeach at 6:10 pm on April 2, 2007

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Ok, I have another kinda strange question that has been haunting me for a couple of years:    

 If you throw some batteries into a bathtub, could a person in it get shocked?  

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Not with ordinary batteries- the voltage is very low- typically just 1.5 volts per cell.  That compares to 120 volts that comes from a outlet.  Also it's DC voltage which requires higher values to shock than AC voltage (like from a outlet).

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Yes, I figured that, but would there be a current in the water, even if it were a low one?  Maybe not with AAs or AAAs, but what about 9 volts?  

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Quote: from ZenaGirl at 3:48 pm on April 2, 2007

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Quote: from palepalepeach at 6:10 pm on April 2, 2007

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Ok, I have another kinda strange question that has been haunting me for a couple of years:      

  If you throw some batteries into a bathtub, could a person in it get shocked?  

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 Not with ordinary batteries- the voltage is very low- typically just 1.5 volts per cell.  That compares to 120 volts that comes from a outlet.  Also it's DC voltage which requires higher values to shock than AC voltage (like from a outlet).

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Yes, I figured that, but would there be a current in the water, even if it were a low one?  Maybe not with AAs or AAAs, but what about 9 volts?  

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People lick 9V batteries. It's not going to do much in the bath methinks.

Post edited at 8:24 am on April 4, 2007 by Just another kid

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Quote: from palepalepeach at 6:10 pm on April 2, 2007

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Ok, I have another kinda strange question that has been haunting me for a couple of years:  

 If you throw some batteries into a bathtub, could a person in it get shocked?

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Not with ordinary batteries- the voltage is very low- typically just 1.5 volts per cell. That compares to 120 volts that comes from a outlet. Also it's DC voltage which requires higher values to shock than AC voltage (like from a outlet).

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I've shocked myself with 600 V at low amperage, and all I did was jump up and yell explitives.  Tasers, used as non-lethal defence, shocks people frm 50-100,000 V.

Small batteries like AAAs wouldn't, but bigger batters with 1A of current or so might be able to do something.  It really depends on many, many factors.

There's a Mythbuster's segment on YouTube about bathtub electrocution.

As for instntaneous change in velocity, think about it.
Acceleration = change in velocity / change in time
A = 10 m/s / 0 s

Uh oh, divide by zero!

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I guess I'll keep walking.

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Being electrocuted is more dependent on amperage than voltage (potential difference).

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Very true, but you have to have enough voltage to overcome skin resistance.  If probes are placed INSIDE the body- a very small voltage can kill- the voltage used by heart pace makers is in the millivolt range, but if pulsed at the wrong time could kill by causing fibrillation or heart block.  But when applied on the outside you must first have enough voltage to overcome skin resistance- which can be several thousand ohms if the skin is dry- then a sufficiently low souce impedance to delivering enough current.  You can generate thousands of volts by rubbing a piece of fur on a balloon but the current is infinitesimal- a few microamps maybe.  Conversely, a car battery can deliver several hundred amps, but only if the resistance is very low- less than a ohm so you can touch a 12V car battery and not feel a thing. It's when you have both high voltage and current that it's dangerous- especially if it's AC.



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