Physics question

Russinating

Russinating

Russinating

Soldato
Joined
27 Dec 2005
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If you start a coin rolling along a surface that is sloped at 1-degree, and assuming the surface is smooth and continuous, will said coin roll at a slow speed forever or eventually reach terminal velocity (close to free-fall speed less rolling friction)?
 
Dumb question but could it actually exceed TV?

I mean, IIRC TV is basically when the forces of mavity and drag even out, but in this case it's rolling not falling so its momentum is also aided by the centrifugal force involved?
 
ubersonic said:
Dumb question but could it actually exceed TV?

I mean, IIRC TV is basically when the forces of mavity and drag even out, but in this case it's rolling not falling so its momentum is also aided by the centrifugal force involved?
Click to expand...


It is falling... just along the surface.
 
It'll speed up until for force of mavity matches the rolling and air resistance (the coin wont' be perfectly cirular and the surface won't be perfectly smooth). Its velocity won't be as fast as dropping it vertically.
 
Roland Butter said:
why does a diesel/petrol car engine need a 5speed gearbox yet a steam train or an electric car doesn't ?
Click to expand...

Because most steam engines and electric motors can produce maximum torque at zero RPM, whilst a diesel or petrol engine has maximum torque way above zero RPM so needs torque multiplication from a gearbox and most times a step down ratio in the drive axle(s.) The clutch also acts as a crude torque converter when slipped on manual transmission vehicles.
 
ubersonic said:
Dumb question but could it actually exceed TV?

I mean, IIRC TV is basically when the forces of mavity and drag even out, but in this case it's rolling not falling so its momentum is also aided by the centrifugal force involved?
Click to expand...
spot the fallacy
 
ubersonic said:
Dumb question but could it actually exceed TV?

I mean, IIRC TV is basically when the forces of mavity and drag even out, but in this case it's rolling not falling so its momentum is also aided by the centrifugal force involved?
Click to expand...


You have just created a perpetual motion machine.The only forces acting are mavity, rolling friction and air resistance. However, a 1 degree slope is not enough to overcome friction so it would come to a stop pretty quickly. If the slope was steeper it would achive a constant velocity lower than free-fall Terminal Velocity (I would guess by the sine, but that's a guess) but would keep going.
 
Chris Wilson said:
Because most steam engines and electric motors can produce maximum torque at zero RPM, whilst a diesel or petrol engine has maximum torque way above zero RPM so needs torque multiplication from a gearbox and most times a step down ratio in the drive axle(s.) The clutch also acts as a crude torque converter when slipped on manual transmission vehicles.
Click to expand...


Reminds me of the prototype Rover gas turbine car, the stall torque was around 3 times the running torque, so it didn't need a gearbox either.
 
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