Physics question

Russinating · 19 Sep 2018 at 09:39

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)?

jsmoke · 19 Sep 2018 at 09:47

I would imagine it would reach TV. Just the time taken to reach TV due to friction.

Dis86 · 19 Sep 2018 at 09:57

Yes, it'll reach a terminal velocity.

ubersonic · 19 Sep 2018 at 10:03

Dumb question but could it actually exceed TV?

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

Minstadave · 19 Sep 2018 at 10:11

ubersonic said:
Dumb question but could it actually exceed TV?

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

No.

Feek · 19 Sep 2018 at 10:13

Terminal velocity for a coin in air isn't actually very fast.

jimjamuk · 19 Sep 2018 at 10:22

ubersonic said:
Dumb question but could it actually exceed TV?

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

It is falling... just along the surface.

Silent Bob · 19 Sep 2018 at 10:31

It'll speed up until for force of gravity 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 · 19 Sep 2018 at 11:46

why does a diesel/petrol car engine need a 5speed gearbox yet a steam train or an electric car doesn't ?

GravyMonster · 19 Sep 2018 at 11:49

A plane on a conveyor belt will land safely if it jumps just as the elevator crashes in to the ground.

GravyMonster · 19 Sep 2018 at 11:51

Roland Butter said:
why does a diesel/petrol car engine need a 5speed gearbox yet a steam train or an electric car doesn't ?

Because the latter have lots of torque.

Minusorange · 19 Sep 2018 at 12:07

In a vacuum or atmosphere or underwater ?

Chris Wilson · 19 Sep 2018 at 12:54

Roland Butter said:
why does a diesel/petrol car engine need a 5speed gearbox yet a steam train or an electric car doesn't ?

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.

dl8860 · 19 Sep 2018 at 12:57

ubersonic said:
Dumb question but could it actually exceed TV?

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

spot the fallacy

Resistance · 19 Sep 2018 at 12:57

http://utdallas.edu/~david.lary/CM/...ter_of_Mass_&_Rotational_Inertia_files/10.pdf

dl8860 · 19 Sep 2018 at 12:58

Spunkey said:
A plane on a conveyor belt will land safely if it jumps just as the elevator crashes in to the ground.

Only if the pilot is a spherical chicken

Meridian · 19 Sep 2018 at 13:06

ubersonic said:
Dumb question but could it actually exceed TV?

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

You have just created a perpetual motion machine.The only forces acting are gravity, 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.

Orionaut · 19 Sep 2018 at 13:12

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.

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.

Orionaut · 19 Sep 2018 at 13:14

Dis86 said:
Yes, it'll reach a terminal velocity.

But what would the TV be if it was on the Moon??

Dis86 · 19 Sep 2018 at 13:15

Orionaut said:
But what would the TV be if it was on the Moon??

Good question - lower gravity but also lower resistances.