Physics question - surely it's just the extra weight?

[Ari]

Got shown this the other day.

http://www.youtube.com/watch?v=X-QFAB0gEtE

Thing is, for all his explanation of the one of the chain hitting the ground sooner due to the chain "whipping the weight around thus making it accelerate faster", surely the real reason is that the one with the chain on hits the ground first simply because it has a blimmin great heavy chain attached to it so it's heavier?

Or am I just being thick? (Again).

[Ledaig]

Irrespective of mass, everything will accelerate at the same rate 9.81m/s^2.

Something to think about is that during the fall the chain will be building up a store of energy as it's velocity increases, as each link in the chain reaches the end of it's permitted travel this energy will be transformed into an alternative form - in this case applied as an additional accelerative force to the remaining length of chain in free fall as well as the weight.

[Einion Yrth]

Ari said:

Or am I just being thick? (Again).

Thick? Maybe, maybe not. You are plainly, however, ignorant of the fact that in any given gravitational field acceleration due to gravity will be identical regardless of the mass involved.

[rhinochopig]

Einion Yrth said:

Ari said:

Or am I just being thick? (Again).

Thick? Maybe, maybe not. You are plainly, however, ignorant of the fact that in any given gravitational field acceleration due to gravity will be identical regardless of the mass involved.

You sure. That's only correct for a vacuum isn't it? Drop a feather and a hammer on earth and the hammer will always hit first.

[Einion Yrth]

rhinochopig said:

Einion Yrth said:

Ari said:

Or am I just being thick? (Again).

Thick? Maybe, maybe not. You are plainly, however, ignorant of the fact that in any given gravitational field acceleration due to gravity will be identical regardless of the mass involved.

You sure. That's only correct for a vacuum isn't it? Drop a feather and a hammer on earth and the hammer will always hit first.

So would a small hammer with the same mass as a feather, one rather leaves air resistance out of the picture on this one.

[Puggit]

rhinochopig said:

Einion Yrth said:

Ari said:

Or am I just being thick? (Again).

Thick? Maybe, maybe not. You are plainly, however, ignorant of the fact that in any given gravitational field acceleration due to gravity will be identical regardless of the mass involved.

You sure. That's only correct for a vacuum isn't it? Drop a feather and a hammer on earth and the hammer will always hit first.

The feather feels the same gravitational acceleration, it's just tempered by friction of the air on the fine fibres. A tonne of feathers all balled up will fall at the same speed as a tonne of hammers!

[Ledaig]

rhinochopig said:

You sure. That's only correct for a vacuum isn't it? Drop a feather and a hammer on earth and the hammer will always hit first.

Acceleration due to gravity is a fixed value (as I mentioned 9.81m/s^2 for the Earth) , the opposing force created by drag is the reason a hammer will impact the ground prior to a feather(which ultimately dictates the objects terminal velocity). Also worth remembering that drag factor increases to the square of the increase in velocity.

[mrmr96]

Ledaig said:

(as I mentioned 9.81m/s^2 for the Earth) at sea level

EFA

[rhinochopig]

Puggit said:

rhinochopig said:

Einion Yrth said:

Ari said:

Or am I just being thick? (Again).

Thick? Maybe, maybe not. You are plainly, however, ignorant of the fact that in any given gravitational field acceleration due to gravity will be identical regardless of the mass involved.

You sure. That's only correct for a vacuum isn't it? Drop a feather and a hammer on earth and the hammer will always hit first.

The feather feels the same gravitational acceleration, it's just tempered by friction of the air on the fine fibres. A tonne of feathers all balled up will fall at the same speed as a tonne of hammers!

Agreed but practically it doesn't accelerate as fast though due to atmospheric friction. Hence the famous Galileo moon experiment.

http://www.youtube.com/watch?v=5C5_dOEyAfk

[Ledaig]

mrmr96 said:

EFA

It also varies due to other factors, but given the question being asked I didn't feel the need to complicate the issue

[deadtom]

I think its kinda related to the feather vs hammer scenario; in this situation both objects have more or less the same atmospheric drag, however the chained weight has more effective mass, meaning the force is greater (F = MA, or in this case Ma where a acceleration due to gravity at earth's surface), so it overcomes the atmospheric drag more easily.

[Eric Mc]

rhinochopig said:

Agreed but practically it doesn't accelerate as fast though due to atmospheric friction. Hence the famous Galileo moon experiment.

http://www.youtube.com/watch?v=5C5_dOEyAfk

Although Galileo was able to prove his point without having to travel to the moon.
He conducted his experiment using ball bearings and a wooden chute.

[blueg33]

deadtom said:

I think its kinda related to the feather vs hammer scenario; in this situation both objects have more or less the same atmospheric drag, however the chained weight has more effective mass, meaning the force is greater (F = MA, or in this case Ma where a acceleration due to gravity at earth's surface), so it overcomes the atmospheric drag more easily.

Huh?

I am not sure what you mean by effective mass? Mass in itself makes no difference to the rate of acceleration or the terminal velocity. The only things that can change the rate of acceleration are additional forces applied.

Air resistance is an additional force acting against gravitational pull, hence an object with high air resistance will have a lower terminal velocity than one with low resistance.

Likewise an additional force applied to the weight in the direction of gravity will call it to fall faster, for instance throwing it down.

This means that the chain must be applying an additional force in the same direction as gravity.

So the question is, what is this force and where does it come from?

The vid suggests that it comes because the chain is pulling on the weight. I am not convinced about this because the pull is potential energy which in this case is a function of g,

Unless I am missing something the additional force cannot come from the chain whipping as the energy input into the chain can only be coming from the falling object so that would actually slow the weight attached to the chain?

Or am I being thick?

Edited by blueg33 on Wednesday 2nd January 17:40

[rhinochopig]

Eric Mc said:

rhinochopig said:

Agreed but practically it doesn't accelerate as fast though due to atmospheric friction. Hence the famous Galileo moon experiment.

http://www.youtube.com/watch?v=5C5_dOEyAfk

Although Galileo was able to prove his point without having to travel to the moon.
He conducted his experiment using ball bearings and a wooden chute.

Of all people Eric I'd have thought you'd approve of spending billions to get to the moon just to drop a feather and a hammer

[tank slapper]

deadtom said:

I think its kinda related to the feather vs hammer scenario; in this situation both objects have more or less the same atmospheric drag, however the chained weight has more effective mass, meaning the force is greater (F = MA, or in this case Ma where a acceleration due to gravity at earth's surface), so it overcomes the atmospheric drag more easily.

Drag probably plays a very small part in this. The velocities are low, and the masses are fairly dense objects (ie they have a small size for their mass, unlike a feather).

As Ledaig said above, this effect is due to conservation of energy. As the links stop at their minimum height, the acceleration as they stop causes a tension in the part of the chain that is still falling. This tension added to the weight force is obviously higher than that of the weight alone. If you consider each link individually rather than the chain as one object, you can see that its mass is constant so the acceleration must be higher as a result of Newton's second law.

[Eric Mc]

rhinochopig said:

Eric Mc said:

rhinochopig said:

Agreed but practically it doesn't accelerate as fast though due to atmospheric friction. Hence the famous Galileo moon experiment.

http://www.youtube.com/watch?v=5C5_dOEyAfk

Although Galileo was able to prove his point without having to travel to the moon.
He conducted his experiment using ball bearings and a wooden chute.

Of all people Eric I'd have thought you'd approve of spending billions to get to the moon just to drop a feather and a hammer

I THINK the astronauts of Apollo 15 had other reasons for going to the moon - like franking some envelopes and selling them on to a dealer .

[rhinochopig]

Eric Mc said:

rhinochopig said:

Eric Mc said:

rhinochopig said:

Agreed but practically it doesn't accelerate as fast though due to atmospheric friction. Hence the famous Galileo moon experiment.

http://www.youtube.com/watch?v=5C5_dOEyAfk

Although Galileo was able to prove his point without having to travel to the moon.
He conducted his experiment using ball bearings and a wooden chute.

Of all people Eric I'd have thought you'd approve of spending billions to get to the moon just to drop a feather and a hammer

I THINK the astronauts of Apollo 15 had other reasons for going to the moon - like franking some envelopes and selling them on to a dealer .

OK there was the Golf

[Einion Yrth]

rhinochopig said:

Eric Mc said:

rhinochopig said:

Eric Mc said:

rhinochopig said:

Agreed but practically it doesn't accelerate as fast though due to atmospheric friction. Hence the famous Galileo moon experiment.

http://www.youtube.com/watch?v=5C5_dOEyAfk

Although Galileo was able to prove his point without having to travel to the moon.
He conducted his experiment using ball bearings and a wooden chute.

Of all people Eric I'd have thought you'd approve of spending billions to get to the moon just to drop a feather and a hammer

I THINK the astronauts of Apollo 15 had other reasons for going to the moon - like franking some envelopes and selling them on to a dealer .

OK there was the Golf

The LRV was created by Boeing amongst others - not VW. ;p

[spikeyhead]

tank slapper said:

deadtom said:

I think its kinda related to the feather vs hammer scenario; in this situation both objects have more or less the same atmospheric drag, however the chained weight has more effective mass, meaning the force is greater (F = MA, or in this case Ma where a acceleration due to gravity at earth's surface), so it overcomes the atmospheric drag more easily.

Drag probably plays a very small part in this. The velocities are low, and the masses are fairly dense objects (ie they have a small size for their mass, unlike a feather).

As Ledaig said above, this effect is due to conservation of energy. As the links stop at their minimum height, the acceleration as they stop causes a tension in the part of the chain that is still falling. This tension added to the weight force is obviously higher than that of the weight alone. If you consider each link individually rather than the chain as one object, you can see that its mass is constant so the acceleration must be higher as a result of Newton's second law.

It's the same mechanism that causes the end of a whip to travel at very high velocities, even breaking the sound barrier.

[Eric Mc]

rhinochopig said:

OK there was the Golf

That was Apollo 14. The 15 crew were more "entrepeneurial" let's say.