Mechanical Physics Question.

[nickyboy]

[QUOTE 4150574, member: 9609"]but this is the bit I can't get my head around.
if it would take 50kgf to push vehicle from rear or the same to push the socket bar at the same diameter as the wheel. Then if that wheel was 1.5m radius then the torque would be 1.5x50= 75kg metres
if the wheel had a 4 metre diameter then the torque created at the nut would be 100 kg metres

I think there is something obvious i am missing here ?[/QUOTE]

You're comparing apples with oranges.

Force applied is measured in Newtons (or Kg x g if you prefer)

Torque applied is measured in Newton metres (or Kg x g x m if you prefer)

Torque is not the same as Force

 

[Cheddar George]

The force at the top of the wheel is going to be 50% of the force needed to push the car from the rear, regardless of the radius of the wheel.

What would cause the 50% reduction ?

My thinking was the same as TVC's, needing the same 50kgf either pushing or using the lever.

 

[Markymark]

What would cause the 50% reduction ?

My thinking was the same as TVC's, needing the same 50kgf either pushing or using the lever.

Is it that the force to overcome the wheel/surface friction acts at either r (radius of wheel) or 2r (top of wheel)?

 

[twentysix by twentyfive]

This is great

 

[Cheddar George]

Is it that the force to overcome the wheel/surface friction acts at either r (radius of wheel) or 2r (top of wheel)?

Okay, i can see where that is coming from.

I am still inclined to go with "r".

 

[Markymark]

[QUOTE 4150618, member: 76"]Even then, all these maths professors will not be able to answer the simple question of will a plane take off if it was on a treadmill.....[/QUOTE]
No, it can't unless there's some other force providing the uplift.

 

[Yellow Saddle]

If the car requires 500N to move it, no matter what lever you use or how you gear the pulleys, it will require 500N to move.

No, it can't unless there's some other force providing the uplift.

My wife's treadmill has a large fan in front. That should do the trick. The problem is, the moment the plane leaves the treadmill, it will accelerate and the pilot will have to de-power the engine neatly so that it doesn't hit the wall. It is the same problem James Bond faces when he, at speeds, drives into a truck with a dragging ramp, also travelling at speed. A front wheel or rear wheel car will require a different approach.

 

[Oldfentiger]

I reckon everyone is over-thinking this.

If you push the car at a point vertically above the axle, at the same radius as the periphery of the tyre, then the vehicle will move half the distance compared to the effort at the periphery.
Pu another way, there will be a mechanical advantage of 2:1, which is the same as a gearing reduction of 1:2.
Therefore the force required will be 25Kg.

 

[classic33]

No, it can't unless there's some other force providing the uplift.

Would it be a plane if there wasn't?

 

[Markymark]

It is the same problem James Bond faces when he, at speeds, drives into a truck with a dragging ramp, also travelling at speed. A front wheel or rear wheel car will require a different approach.

The Italian Job showed how to deal with that neatly.

 

[Yellow Saddle]

We don't need to know how long the lever is. Fact is, that car will only move if you apply 500N. Essentially this means the car pushes back at 500N and no matter what, it will still push back at 500N and all the Newtons are going through the soles of your feet. You have to apply 500N to the lever.

 

[Yellow Saddle]

The Italian Job showed how to deal with that neatly.

Did it end as badly as I've also thought it would end? I didn't see the movie or fell asleep, can't remember which.

Edit: I meant to say, did the "drive into a truck" incident end as badly as I always thought these the things should happen in real life. On long car journeys I often think of slipping, Bond style, onto a passing flatbed and push my seat back and fall asleep. But consider the question rhetoric.

 

[Markymark]

Did it end as badly as I've also thought it would end? I didn't see the movie or fell asleep, can't remember which.

It ended as a cliff -hanger - literally....but that was not the bit about the cars getting into the lorry though, they managed to do that quite neatly.

 

[Tim Hall]

[QUOTE 4150618, member: 76"]You have missed the point of this type of thread entirely.

This isn't about who can solve the problem, it's about who is the cleverest mathsy type person, so there will be lots of KGmn x Torque Radius/ Rotational Gyroscopic leverage force x velocity mass if the Gimble offset is above the fulcrum as opposed to below the fulcrum gibbet type bollox.

Even then, all these maths professors will not be able to answer the simple question of will a plane take off if it was on a treadmill.....[/QUOTE]
And smartarse grammar pedants will start bemoaning the lack of the subjunctive.

 

[Oldfentiger]

If you examine the cycloid curve.........

If the vehicle is travelling at say 10mph, the only part of the wheel that is doing 10mph is the centre.(relative to the ground.
The bottom of the tyre is travelling at 0mph, relative to the ground.
The top of the tyre is doing 20mph, relative to the ground.