Why Does Stepping On A LEGO Hurt so Much?

James asks: Why does it hurt so much when you step on legos with bare feet?

legos2Right up there with how the gun on the original Duck Hunt game worked, why it hurts so much to step on a Lego brick is one of the questions we’re asked the most, so it’s high time we answered it. As anyone who’s done it knows, stepping on a Lego block is something akin to being shot in the foot by a knife soaked in wasp venom. In truth, this is an inherent danger of allowing a child to exist in your home.

While we’ll never know who was the first person to step on a Lego block and curse the day Kirk Kristiansen “borrowed” the idea of Lego bricks from the patented “Kiddicraft Self-Locking Building Bricks,” we can answer the question of why stepping on one of the little buggers hurts so much more than many other common household items. The answer partially lies in how insanely sensitive to pressure, pain and practically everything else our leg-hands actually are.

The soles of the feet are one of the more sensitive areas of the human body, right up there with things like the lips, genitals, eyes and hands in terms of how sensitive to touch and pain stimuli they are. If you’re wondering why our feet need to be this sensitive, it’s because our feet are constantly working to keep us balanced and the information from the nerves in them are vital for allowing the brain to adjust accordingly to keep a person from falling over.

But why is this such a major complaint of Legos and not so many other items? We mean, stepping on anything sharp and pointy is going to hurt, so why is it only Lego bricks that seem to be so often mentioned?  Well, according to Lego, there are enough Lego bricks to give every person on Earth 83 bricks each. So you’re bound to come in contact with one and, unlike sharp objects, people aren’t as careful to keep them off the floor; often that’s where kids play with them.  Just as important is that unlike many objects which tend to have some give to them when you step on them, a single standard brick of Lego can be subjected to approximately 4,240 Newtons of force before it deforms.

This means a single, lowly Lego brick can support weights in excess of 432 kilos (953 pounds) before it reaches its breaking point and compresses. So when you step on a Lego brick on a relatively solid surface, there is nowhere for the force you’ve just exerted to go but right back into your foot and into the huge cluster of nerves it contains. This is compounded by the fact that the bricks have little knobs, relatively sharp corners, and the soles of the feet are subjected to impact forces that can be equal to around 9 times our own body weight while moving; even walking slowly can produce impact forces equal to double your body weight.

For an example, a standard 2×2 Lego brick has a surface area of roughly 2.25 centimetres squared (for the sake of simplicity we’ll ignore the studs, which certainly aren’t going to help matters for your foot anyway). Let’s say a person weighing 75 kilos (165 pounds or 734 Newtons) steps onto it.

Now, the pressure on a given object is equal to the force applied divided by the area over which it is spread (P=F/A).  So even if that 75 kilo person were just standing on the Lego with one foot, rather than having their foot accelerating downward at some rate as with walking, this gives us 734 N/0.000225 m2 = roughly 3,262,222 pascals of pressure! For reference, that is roughly 32 times standard atmospheric pressure, all suddenly forcing its knobbly, unforgiving way against one of the most sensitive regions of the body.

Of course, part of the rest of your foot will ultimately support some of your weight on the floor, taking quite a bit of the pressure off once that happens.  On the flipside, your foot will be stomping at some force downward skewing things the other way significantly (as mentioned, even walking slowly, the impact force can easily equal double your body weight, let alone if you’re walking quickly); so this is just a very rough calculation, that nonetheless demonstrates how stepping on a Lego brick can produce some relatively large forces on the area of the foot the Lego brick is contacting.

So, to answer the question posed, the reason stepping on a Lego brick hurts so much is a combination of how sensitive the nerves in our feet are, how much force our feet hit the ground with as we walk, and the fact that Lego bricks are extremely rigid, somewhat jagged, and small, ensuring that the force is efficiently directed back into a tiny area of your foot. May God have mercy on your soul if you step on a Lego brick that is on a tiled, rather than carpeted, floor.

If you liked this article, you might also enjoy our new popular podcast, The BrainFood Show (iTunes, Spotify, Google Play Music, Feed), as well as:

Bonus Fact:

  • In the late 1940s, a company called Kiddicraft began manufacturing “Kiddicraft Self-Locking Building Bricks”, which were patented by Hilary “Harry” Fisher Page.  Kirk Kristiansen, the founder of Lego®, came across these bricks in a demo he was shown of an injection molding machine.  He then copied these bricks and sold versions of them under his own brand as “automatic binding bricks”.  It isn’t clear whether Kristiansen knew these bricks were patented or not at the time or just saw the potential of such a small plastic brick as a toy product when observing the injection molding machine demo.  Lucky for him, Page died without ever finding out Lego® had copied, and was selling, a version of Kiddicraft’s product illegally. Some 31 years later, Lego® acquired Kiddicraft when Lego® was preparing to, ironically enough, sue Tyco for illegally copying Lego’s bricks; hence, to strengthen their case, they needed to own Kiddicraft and the original patent.  In the end, they lost the case anyway and Tyco got to continue selling the bricks, which at the time were earning them about $20 million annually.  So the $3 million Tyco spent in the legal battle with Lego® ended up being well worth it.
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  • My son leaves 100s of these landmines all over his room and I must have stepped on a dozen of them. Now know why it hurts so bad. Good thing his room carpeted or it would hurt more.

    • From the standpoint of a physicist, I assure you, it doesn’t matter that the floor is carpeted, since your weight is represented by your normal force (the force with which the floor pushes back on you to counteract gravity), so it is the same no matter what you step on.

      Sorry for the late reply, though.

      • You may be a physicist but you may not now that carpets are laid on top of a underlayment which is a giving material an cushions your steps… see where I’m going ? Your foot has a wider area than the lego brick and will cover it. The parts of the foot that don’t rest (ouch) on the brick will rest on the carpet over the underlayment. Everything will push down. The brick will sink more than the rest of your foot and that will relieve some of the pressure… the majority of the foot area is still somewhat supported, applying less pressure.
        Sure the pain is still feels pretty much the same, however, if you compare stepping on bricks on bare ground and carpeted ground, pick the carpeted ground always.

  • Freaking plastic caltrops!

  • “Why Does Stepping On A LEGO Hurt so Much?”

    Because it’s hard and has sharp edges. Did we really need a whole article for that?

    • @Vince: The edges don’t have as much to do with it as other factors, so apparently. 🙂

  • Stepping on a small Hot Wheels car is no walk in the park either.

    • My son leaves little plastic planes around and when you step on one of those, you know how hard you can throw a plastic toy across a room while crying in pain.

  • SloppyFrenchKisser

    I let my kids play with jagged rusty cans and glass shards. Now those really hurt when stepped on.

  • Shot in the foot by a knife?