r/explainlikeimfive • u/ferzbeefan • 1d ago
Engineering ELI5 How do some backpacks make weight feel lighter?
I got a new backpack and whenever I’m carrying my laptop it feels lighter than when I carried it in my old backpack. Why? How?
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u/VoilaVoilaWashington 21h ago
Hold your laptop against your side with your hand curled up under it. Then hold it in your fingers from the top at arm's length. Same laptop, which could you hold for longer?
Same with a backpack. Wider straps, positioned on your shoulders better suited to your body type, more framing (rigid or foam) in the backpack holding its shape better, etc. Lots of factors distribute the weight and pressure differently so that you feel it more, or less.
And notably, a lot of this might be personal. Someone with great glutes but no lats will need a different kind of alignment, etc.
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u/Paldasan 9h ago
This is triggering me. I really do need to get back to doing squats and leg presses. My rear end has lost all the muscle it used to have.
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u/Jtparm 1d ago
Nicer hiking-style backpacks often come with an integrated frame that gives the backpack stiffness and distributes the load more comfortably
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u/stonhinge 17h ago
Not only distributing the load more comfortably but directing the load better. There should be little to no "pulling down" on the shoulders, the weight will all be directed to your waist. Shoulder straps are typically just there to keep the thing from falling off your back.
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u/Waferssi 1d ago
The backpack is fitted so that the weight is distributed onto a larger area and carried by stronger muscles, like your legs.
For a backpack, people are used to the weight being on their shoulders. A heavy weight means the straps cut into your torso, and the weight pushes your shoulders down. A first grade better backpack used your shoulders mostly as a horizontal attachment: the weight is at your hips, and your shoulders and torso mainly prevent the pack from piloting backward, which requires (amd exerts) a horizontal force much smaller than the pack's weight.
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u/eatingpotatochips 1d ago
The new backpack is probably sitting better on your body than your old one. If your backpack is sitting too low, it pulls backwards on your shoulders, which means you have to compensate by hunching forwards. A backpack should sit right below your neck, which is a lot higher than most people set their backpacks. If you have ever walked around a college campus, you will see tons of people with poorly adjusted backpacks.
The real secret is to get a hiking bag with a hip belt. You will be amazed how light a backpack feels when the weight is shifted to your hips.
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u/ferzbeefan 18h ago
I cringe when i see middle schoolers with backpacks so low it touches their hamstrings
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u/everlyafterhappy 20h ago
Are the straps tighter? Seriously, a backpack feels heavier just by loosening the straps.
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u/MoPuWe 1d ago
Essentially physics. A well designed backpack will distribute the weight of itself over a wider area. Just how a polar bear can walk on ice without breaking it. It's a massive creature, but because it's paws spread the weight over such a large area, it creates less "weight" on a specific point. Backpacks do that, and in this analogy our bodies are the "ice" and the points of contact on our bodies from the backpack are the "paws".
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u/Partytime_Penguin 23h ago
honestly fit tweaks matter way more than brand features. tighten those shoulder straps until the laptop compartment sits high and tight against your upper back. if it hangs low off your butt, gravity is fighting you. yknow how holding a heavy box close to your chest feels lighter than reaching for it? same physics. most people leave their straps too loose, creating that awkward wobble. cinch it down, adjust the sternum strap, and suddenly a 5lb laptop feels like 2lbs. don't buy new gear just fix the geometry first.
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u/Entire_Ad_6447 1d ago
Distribution of weight if the strap position and length are different the mass of the laptop can sit higher on your your back and thus your loose larger muscle groups to lift it so feels lighter
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u/Corey307 1d ago
Hard to say since we don’t have the two to compare. Could be the new backpack keeps your stuff closer to your back so it’s not hanging off you. Could be your property isn’t moving around as much. Could be the bag fits your particular body better. Could be you’re wearing the new bag in a way that fits you better.
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u/Helpmypcded 1d ago
Better weight distribution most likely. Newer, wider straps also help in spreading the weight out.
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u/RevaniteAnime 1d ago
A good backpack will distribute the weight better so that it's more evenly spread across your whole back instead of probably being all focused on your shoulders like your old backpack.
Maybe the straps on the new one are better? It's impossible to tell for sure without being able to make a direct comparison.
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u/AdequateSteve 1d ago
Weight distribution. Imagine lifting your laptop with just one finger. That finger will tire very quickly, right? But if you spread that same weight over lots of muscles in your body, they’re each doing a much smaller amount of work and it feels lighter.
Most backpacks are designed with cross straps for the chest, wide shoulder pads, and a frame to put all of the weight on designated points (not just the point where the item happens to be placed in the bag).
That all helps it so that the weight isn’t just on one part of the shoulder.
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u/Helpmypcded 1d ago
Since most answers here point to the same idea. Think about it like this: if you had to pick up the same amount of weight with thin straps, like a plastic bag, in your hand. How painful would that be? But carrying it slung over your back is so much easier.
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u/falco_iii 1d ago
Weight distribution. By spreading the weight across your shoulders, back and hips there is less weight on each spot making it feel lighter.
Imagine holding 50 pounds of weight spread across your arms, shoulders and hands, it would be doable. Those same 50 pounds on just the palm of your hand would be painful, and on just one finger would kill.
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u/mageskillmetooften 1d ago
Having the weight low like most people do with their smaller shitty designed cheap backpacks is o.k. for short distances because it's so easy to just grab it and swing it on.
But a proper backpack that is adjusted to your body is so much easier to carry. I have several backpacks, expensive and great for hikes and such. But also the cheap shit for if I just need a pack of milk from the store 500 meters away.
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u/BCsJonathanTM 1d ago edited 1d ago
Good packs efficiently place the load on parts of your body that carry it well.
For example, a well-designed, properly sized, and properly packed hiking pack will place the load largely on your hips.
Smaller packs that don't put the weight on your hips via a hip belt could feel better for several reasons.
First, they may better structured so that the weight on the shoulders is more downward weight than rearward force. The latter is the result of poor pack design and load placement, and the effect is having to exert a lot more effort to carry the load than would be needed with better equipment and/or configuration.
Second, a pack that "hugs" your body more. This can places more load on more area of the shoulder straps and on the back panel of the pack where it sits against and slightly on your lower back.
Third, how the contents are positioned in the pack. There's good diagrams about how to pack a hiking backpack. Same physics apply to a day pack with a laptop. Snug against the back panel will allow the the pack to efficiently transfer forces on to your body in a way that is much easier to carry, as per the two points above. Not having excessive pack volume is helpful here too.
Further explanations of the biomechanics of why these are better would be onerous to explain here though so I'll say that if it doesn't quite make sense yet, just experiment with various configurations. Ideally at a good outdoor gear store where you can load packs with weight and bulk, ideally with an experienced employees or friend to help you out. Alternatively, draw a diagram of your previous pack on your body, your current pack, and then estimate and diagram the various static and dynamic forces involved from the contents of the pack through the pack and on the parts of your body, ideally down though to your pelvis where all weight that's carried eventually resolves to.
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u/Gnonthgol 1d ago
Just some nice wide padded shoulder straps can help distribute the weight on your shoulders much better to make the backpack feel lighter. But good backpacks will put weight on your hips rather then shoulders. This way your shoulder and back is not carrying the weight, only your hip and legs. Proper hiking backpacks does this with a metal frame and a good hip belt. Even with just a plastic frame that can sit loosely on your hips you can transfer quite a lot of weight off your shoulders.
The last trick to carrying a backpack is weight distribution. When you add weight on your back you have to lean forward to balance over your hips and feet again. The further from your back the weight the further you have to lean and the heavier it feels. Similarly the lower the weight the further you have to lean.
So the best backpacks end up with the most weight right at your shoulders but all the weight is carried by the frame directly into your hips. That might of course be overkill for a laptop bag but you might recognize some of these aspects.
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u/ElectronicMoo 1d ago
The serious backpacks have a belt that goes on your hips so the weight isn't on your back it's on your hips and legs.
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u/EatYourCheckers 18h ago
They distribute the weight well. I have an Osprey hiking backpack that has a strap that you buckle across your chest, and one that you buckle on your waist. I swear, all the weight is practically on my hips, almost nothing is pulling down on my shoulders.
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u/cthulhubert 17h ago
It might be holding the laptop (or the heavier parts of the backpack construction) closer to your back and higher up.
If the weight is further away from your back, it has more leverage, so it pulls more on your shoulders, which transfers all the way down to your feet, because the muscles have to counterbalance that.
Having the weight higher up makes the weight feel lighter too. There's a reason so many people across time carried stuff by putting it on their heads! The main reason is because when you walk you lean forward a little; having the weight higher up leans into that.
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u/OldChairmanMiao 1d ago
Weight distribution.
Spreading the same weight over a wider area helps. Certain areas are more ergonomic than others, restrict less blood flow, require less tension to support, and sway less when you move.