Physics Life Hack: How to Remove a Fence Post Set in Concrete with a Lever

Fence posts are often set in concrete to keep them stable, which is great ... until you have to remove them. I've seen people dig all around the concrete to free the post, but that is way more digging than I want to do. Instead, you can make a long lever to remove it without any digging at all!
A lever is just a stiff arm that can pivot around some point (the fulcrum) such that you can apply a force to one part of the arm and get out a force from another part of the arm. This can be used to change the magnitude or the direction of a force, making a small force large or an upward force downward.
This mechanism hinges on (sorry, couldn't resist) the idea of rotational equilibrium. As long as the arm is at rest or moving at a consistent speed, the total torque on the arm must be zero because its angular acceleration is zero. When you use a lever to lift something, these conditions are typically met exactly or at least approximately.
If we use the fulcrum as our axis of rotation for the calculation, then the force from the fulcrum does not contribute to the total torque on the system, only the input and output forces do. This means that the torque caused by the input force must be equal to the torque caused by the output force.
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Technical note: More accurately, the torque from the input force must be equal in magnitude to the torque from the third law pair force to the output force. If we use the lever to lift a rock, we're talking about the force that the rock applies to the lever, not the force the lever applies to the rock. These two forces will be equal in size, as described by Newton's Third Law of Motion.
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The magnitude of the torque here is equal to the magnitude of the force multiplied by the distance from the pivot to the location of the force. If the two distances are different, the forces must be different as well to make the torques equal. For example, if the input force is 2 meters from the fulcrum, but the output force is only 1 meter from the fulcrum, the output force must have 2 times the magnitude of the input force.
To lift a post out of the ground requires a huge amount of force. To achieve this without special machinery, we simply need to place the input force much farther from the fulcrum than the output force. In this video, I applied a force to the lever a distance 10 times that of the output force on the post, making the output force 10 times that of the input force.
There are three classes of levers. A first-class lever has the fulcrum in the middle of the two forces, like a teeter-totter. A second-class lever places the output force in the middle, with the input force on one side and the fulcrum on the other. The lever in this video is a second-class lever, as is something like a wheelbarrow. A third-class lever has the input force in the middle, with the output force on one side and the fulcrum on the other. A lacrosse stick or a human forearm are examples of a third-class lever.

[@benmadley7778]

I have to give you credit, because you my dear sir, understand the fundamentals of LEVERS and LEVERAGE. Good post.

[@TonyChanTurbo]

"Good post". Good pun 👍

[@roberte7606]

Spent an hour this morning prying 4 posts out with a thirty pound pry bar, trying to wedge between the side and the ground. I knew there had to be a better way. Me and my aching spine will be thanking you in short order. Thanks dude!

[@youtuuba]

Good and well explained demonstration of leverage. Science! However, as an Engineer, I can hopefully contribute some additional helpful refinements! - The taller you make the fulcrum above the ground, the higher you have to lift the Effort end of the lever to achieve the same lift distance at the Load, so a flat board for the fulcrum might have worked a bit better. - Besides the primary goal of achieving the necessary lift at the Load, an important secondary goal is to lift the Load enough to easily clear the ground. Moving the Load's attachment point a bit further away from the Fulcrum can give substantial improvements in lift distance, with minimal increased Effort. - There is no advantage in screwing the Load's pivot bolt/screw into the Load. Simply drilling a clearance hole in the Load (and the lever, of course) and slipping the bolt through is sufficient; easier to set up and to dismantle later on. There is plenty of friction on the bolt once you start applying Effort to keep the bolt in place. - The bolt hole in the lever should preferably be closer to the top edge of the lever, rather than centrally located; less chance of tear-out. And there is also room for some casual empiricism. Having used this same method to pull posts previously, I have settled on an 8 foot long 2x4 board as the lever, and a 3/8" diameter steel bolt, with a 5/16" diameter clearance hole. On my first attempt, I tried just using a brass 1/4" rod that I had laying around, and it turns out that the approximately 50 pounds of effort I was applying, resulting in over 500 pounds of lift at the Load, exceeded the shear strength of that brass rod. I have never tried using a bolt larger than 3/8", and indeed doing so would jeopardize the strength of the lever at the Load's pivot point . Cheers!

[@robertfusselman8108]

Why not just use a farm jack with chain and S hooks done lmao

[@youtuuba]

@robertfusselman8108 , laugh all you want I know better. This method does not require owning or purchasing any equipment other than a 2x4.

[@edurbanik2842]

What size hammer did you use to drive that 3/8 diameter bolt thru the 5/16 diameter hole? Add to shopping list.

[@edurbanik2842]

Do you have a stash of 3/8 diameter bolts that are at least 4 inches long that nobody else on the face of the earth has stashed away? Reminder: To get thru a 4x4 and a 2x4 the bolt will be at least 6 inches. So maybe you had to buy that bolt. Add to shopping list. If you want a flatwasher and nut, let's just add them to the list.

[@edurbanik2842]

I just got done calling 100 random people from the 2024 local phone book. None of them was willing to admit to possessing a 8 foot long 2x4. Imagine that. ( I keep 3 10 footers stashed in an undisclosed location. ) Add one 8 foot 2x4 to shopping list.

[@timothykatch1855]

The giant lever is a great idea, it helped me a lot. Thank you.

[@oswaldcassanova8941]

A compliment on everything, best video I have seen so far.

[@tonyalways7174]

That’s a great demonstration and very useful . Thanks for sharing

[@SourPowerGamer]

Can’t wait to give this a try! Thank you

[@brewmeisterjosh]

Tried it. Totally worked, thanks man

[@emanuelmota7217]

Great idea! Will try it.

[@MrDambler77]

One of the best demos I've seen in a long time....well done Sir! I have learned something today.

[@paulgates5552]

Thanks, posts came out perfectly, saved a lot of time trying to dig them out. 👍👍

[@AndrewBennettScience]

Glad it helped

[@bossman8303]

Thanks , I learned something today.

[@alastairwoodford5180]

Why wouldn’t you want to know this stuf?!?! Love it

[@plk5520]

I'm going give your method a shot because I have the necessary materials and tools at hand. I'll be trying to remove a 6 by 6 wooden fencepost that's buried 24 inches below ground, embedded in a concrete footer. Anticipating the necessity for adjustments I'll use a carriage bolt instead of a screw and I think a length of chain will come in handy. I really like the idea of doing it this way. The magic of physics and all that. If I don't achieve success I'm prepared to purchase an inexpensive bottle jack which will also come in handy for removing a couple of small tree stumps and any future fenceposts, of which there are plenty.

[@JohnWillman]

Right on,..great idea for the home owner,..I have a NW Quik Pull,.. how did you break the concrete after you got that huge set out?

[@barrytanenbaum4157]

Good Job!

[@Yourfavbrunette530]

Thank you so much for this video! Tried it today, and it worked like a charm. Let me add that I had to take a shovel and separate the dirt from the concrete all around the perimeter to give it a bit of help.

[@seymourscagnetti1413]

Applied Science. Nice.

[@doogiemcdougster6740]

Goliath: That little screw.... Mmm, I don't know, Davie. You later: Yeah, that didn't work. Good video. Thanks. :)

[@mariamejia7740]

If physics were thought like this in school we would had better grades and a better understanding of rhe world. Thanks. I will try this for sure.

[@MichaelOnines]

Now you have a free concrete mass to use in the Cavendish experiment!

[@AndrewBennettScience]

Reduce, reuse, recycle! I love the eco-friendly thinking!

[@jaccounts4659]

I wrapped a chain around a post simuliar process it worked

[@georgekaiwai]

if you tie rope around the plank and post where the 2 are touching or where you put the bolts that will also work

[@emy840]

Post is in ‘tight’ but you could shake it loose before you even jack it up. Lol

[@mikescalise8380]

I have posts that are three feet in the ground, how can I get them out without demolition?

[@wandadoney8344]

I'm looking for a way to get the Remaining rotted clothesline post out of a bucket of cement without digging the bucket out of the ground. Any ideas a woman or 11 or old boy could use??

[@orpheusuk8762]

Absolutely excellent. I'm going to try this method on six posts within the next seven days. I'll report back.

[@MrAlvaro2376]

Did it work ?? Cause Im replacing Six Wooden Post

[@orpheusuk8762]

@@MrAlvaro2376 Yes, it worked perfectly. Old concrete around the base of old post can be too heavy to pick up even when it's outside the hole. So, pulling it upwards through soil is a task requiring 'method' as opposed to brute force. Try this method [explained in video]. You'll be glad you did.

[@MrAlvaro2376]

Thanks !!

[@ironeagle22a]

This was like a Sesame Street episode. Even a three year old could understand.

[@kentjagger6291]

This worked well for me, and was much cheaper than buying a highboy jack.

[@nathanaelcard]

I'm here for this #levercore yardwork

[@willo9372]

Took me ages to convince my boss to try this. Once his old head got around the idea, my back felt a lot better.

[@dorothyvassallo7768]

Please Andrew - when editing turn down the volume of the music....those who are hard of hearing may have trouble hearing your voice. Thanks

[@user-xx7pg3vw9k]

but what do you do when the post is broken and you need to get the concrete out of the ground?

[@bdoogy1]

Unfortunately, I only know about digging down enough around the concrete to wrap a good chain around the concrete mass. Then, attach the chain to your lever to get it out.

[@robertfusselman8108]

This worked or use a farm jack with a chain and S hooks:-)

[@RichardsMovies]

Why wasn't the fulcrum between him and the post? It would be a lot easier to extract if he was pushing downward on the lever instead of trying to lift it

[@TygwynD]

Chet Arthur You’d never be able to get the range of motion required - look how high he pushes the beam ‘up’ for a small movement. The ground would get in the way of you pushed down.

[@cinnoraamann9519]

Your smart.

[@ailtire2117]

You're*

[@danielledoyle60]

My bolts kept snapping/bending :/

[@OU81TWO]

You rotated the post out and did not lift it straight up. It work because you have relatively soft earth surrounding the concrete which was only about 18"-24" deep from the looks of it. Now try this with a post set 5 ft in the ground. Never it a million years would it work.

[@AndrewBennettScience]

That's fair - it likely wouldn't work. I suspect that most people looking to remove a post like that are doing this in more of a professional capacity and have access to some heavy equipment to facilitate the process. Must be a heck of a fence that has a post buried 5 feet! I would be interested to see if you could make this process work by adding an alternating pivot system. I think that you could increase the maximum capability of this system by lifting as high as you can (not nearly as far for a deeper post) on the lever as shown, then wedging a stack of boards under the lever on the near side of the post, then pushing down on the board as far as you can and wedging another board or two under the lever on the far side of the post. You should be able to seesaw it out, without ever tilting the post very far. Maybe not enough of an improvement for the scale you described -- might be worth a try, though!

[@OU81TWO]

@@AndrewBennettScience I northern climates like where I live if you don't go down 4ft minimum frost heave will move the concrete over time. Stacking blocks as you suggested to keep the pivot point moving upward with the post as it lifts is a good idea. It will limit the tendency for rotation. In addition to that, use two people and 2 lever systems 180 degrees apart. This way the post comes up straight and you double the force.

[@ExitPlanner]

good job... better to use you noodle than your back! !

[@Nightl3lade]

nice, faster than using a bottle jack

[@scooterbro788]

If you move 9.6” on 96”,that would leave 9:1 on leverage end.

[@AndrewBennettScience]

Since it's a 2nd class lever, the fulcrum is all the way at the end of the board. The input distance is basically the full length of the board (minus the distance that my hand takes up at the end of the board). The pivot isn't at the bolt location, it's where the 2x4 touches the board that's board that's lying on the ground. I think you're using the appropriate thinking for a first class lever, where the pivot is in the middle, somewhere between the input and output forces.

[@joew4202]

6:20

[@MarkKrisburg]

Instead of breaking your back, create a fulcrum with pieces of 4x4 on the other side of the past, and then apply your body weight pushing downwards on the end of the long board to do the lifting.

[@AndrewBennettScience]

I had considered that, too. My guess (before trying this) was that this was going to be a lot harder than it was, and I figured a could lift with a bigger force than my body weight. I thought I might need every last pins of force I could generate. I'm this case, moving the fulcrum and sitting on the board would have worked great. If the post were deeper, with more concrete, I might have needed to be lifting. Of course, a deep enough post with enough concrete, and you probably just break the 2x4 before you move the post.

[@MarkKrisburg]

@@AndrewBennettScience Also, many videos show pulling posts from dry soil. Saturating the soil around the post with water could make many easier to pull out. Dry clay or compacted DG soil is particularly strong when dry but weak when wet.

[@laptruong2107]

if you got a rotten post then digging is the only method ...

[@chucks4748]

Lol. I don't think that post was in there tight when you wiggled it pretty easy. Your way of removing a post in concrete would never work in Texas clay soil.

[@jonathanlavery]

Not true. My neighbor pulled out 9 post using this exact method. We live in Texas

[@roberte7606]

Give me a lever long enough and a fulcrum on which to place it, and I shall move the world. -Archimedes

[@jeremiahbullfrog9288]

Saturate the soil to loosen the clay. Or just give up, pay someone to do the job, and learn nothing.

[@antsher7001]

why isnt there more videos of this. if you can create a fulcrum. either with screws. or like i want to try is using ratchet straps in the same basic manner. this is the thinking that makes me realize how far we have fallen as a civilization. there is absolutely no physics . nothing but jacks in all these videos. in theory. u can lift anything out of the ground with the right fulcrum,

[@Wedgestand]

Ugly fence, nice lever.

[@curranservices]

Good post (nudge, nudge, wink, wink)