Profound Query of the Day

xsnv said:
You forgot your "a" in the "2s" term. It should be "2as" otherwise your equation is not dimensionally consistent (m/s divided by m is per second. multiply that by mass and you get m/s...not the units of force)

you need to fix either a or t

You see now?
Click to expand...
I don't really understand this.

Can I try another analogy?

If I'm driving at 10m/s and want to stop in 50m, is it impossible to work out my deceleration (assumed constant)?

u=10
v=0
s=50

v^2 = u^2+2as
=> a=(v^2-u^2)/2s

Is that mathematically illegal?

edit: You've removed your post. I'm going to leave my quotation there for effect ;) :p
 
yeah, made a blunder! just realised this though...his deceleration can't be constant. If it was he'd start travelling the other way after his velocity got to 0 !!!!!

What do you think? His deceleration can't be constant. His velocity gradually decreases to 0. His final velocity is fixed. If his velocity didn't decrease it would go to 0 instantly hence infinite deceleration1
 
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p4radox said:
I don't really understand this.

Can I try another analogy?

If I'm driving at 10m/s and want to stop in 50m, is it impossible to work out my deceleration (assumed constant)?

u=10
v=0
s=50

v^2 = u^2+2as
=> a=(v^2-u^2)/2s

Is that mathematically illegal?

edit: You've removed your post. I'm going to leave my quotation there for effect ;) :p
Click to expand...

edit: hang on there, rewriting something :o

Yep, draw a graph of v/t

50 metres is the area [of the graph], which is the distance travelled
10 m/s is your start velocity

You want to know the gradient of the graph (your decceleration).

1/2 vt = 50m

You know v, so solve for t...
t = 10 seconds

You need to deccelerate at 1ms^-2
 
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What do you think? His deceleration can't be constant. His velocity gradually decreases to 0. His final velocity is fixed. If his velocity didn't decrease it would go to 0 instantly hence infinite deceleration!

lol
 
daz said:
edit: hang on there, rewriting something :o

Yep, draw a graph of v/t

50 metres is the area
10 m/s is your start velocity

You want to know the gradient of the graph (your decceleration).

1/2 vt = 50m

You know v, so solve for t...
t = 10 seconds

You need to deccelerate at 1ms^-2
Click to expand...

Deceleration would be 1m/s^2...
Anyway, that's not my point. Isn't my analogy with the car analogous to the one with the guy in bubble wrap?

edit: you spotted your mistake anyway. Damn, people are quick tonight!
I know how to do the sums, I was just questioning xsnv's reasons for discounting my method. :)
 
xsnv said:
What do you think? His deceleration can't be constant. His velocity gradually decreases to 0. His final velocity is fixed. If his velocity didn't decrease it would go to 0 instantly hence infinite deceleration!

lol
Click to expand...

Constant decceleration, not constant speed.
 
bah i give up! I see your point and tbh I can't argue against it right now. I can't think clearly enought to. You might be right actually.
 
Aha...it's the time over which the force acts that determines it's effect i.e the impulse of the force. I went about the wrong way trying to prove this (and i was found out pretty quickly) but *** concept was the same.

Impulse of Force

The product of average force and the time it is exerted is called the impulse of force. From Newton's second law

the impulse of force can be extracted and found to be equal to the change in momentum of an object provided the mass is constant:
Calculation
The main utility of the concept is in the study of the average impact force during collisions. For collisions, the mass and change in velocity are often readily measured, but the force during the collision is not. If the time of collision can be measured, then the average force of impact can be calculated


something along those lines anyway. I was wrong with the fixing acceleration and time thing. this time is the time over which the force acts not the time over which the body decelerates. i got them mixed up.

This i do know though. its the change in momentum hence impulse that characterizes collisions and this is dependent on time
 
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What about if we fill the bubbles with helium?

The gathering crowd would all sound like Joe Pasquali.

'He's dead!'
 
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You're all forgetting one important thing :

With all that tension sheet to play with, the person wrapped inside would be so relaxed by imapct time he wouldn't care!! :D


See the Red Dwarf thing I did there? ; )
 
Mickey_D said:
You're all forgetting one important thing :

With all that tension sheet to play with, the person wrapped inside would be so relaxed by imapct time he wouldn't care!! :D


See the Red Dwarf thing I did there? ; )
Click to expand...

OMG! Someone in America watching Red Dwarf! A WITCH!!!
 
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