The Physics Problem Students Keep Getting Wrong: Two Static Blocks Hung From a Spring Scale

This is a classic application of Newton's Laws. It makes a great demonstration of static force, equilibrium and Net Force.

Two masses are hung from opposite sides of a pulley. In between is a spring scale. What is the force reading on the scale?

Most people will report the answer to this physics problem wrong the first time through, thats ok, it's called learning!

This demonstration often comes up in introductory physics courses including AP Physics

[Binary_Omlet]

Dude is a FANTASTIC teacher. That was explained simply and concisely so that anyone can understand it.

[EvilMastermindOfDoom]

Also here from the dude on reddit. Went "OOOOoooohhHH!" out loud.

[leonleszczynski]

Plot twist: Dude from Reddit is the dude in the video

[Alphinell]

ty reddit for introducing me to this physics problem that ill never have to answer in my life

[ptyptypty]

physics RULES!! your demonstration is what teaches this principle very nicely... I think it was early on in my physics that it was all the Counter Intuitive revelations that Physics presented. Other examples are why a Bowling ball goes down a ramp faster than a Tennis ball, moments of inertia, or why a 20 ton Semi Truck will stop in the same distance as a Bicycle assuming they have the same coefficient of friction tires and starting speeds... etc etc... amazing.. Thanks again for your videos..

[WxBuggin]

In case you're wondering where the heck we all came from on Reddit - there's a post on r/theydidthemath posing this scenario, and someone linked it.

I'm glad they did! You're awesome at explaining all of this in a way that's straightforward and easy to understand...instead of clickbaity. My teen will appreciate your channel too ☺️

[faredoondastur]

Thank you very much for this explanation. While doing a textbook question, I came across such a scenario, and was under the false impression that the forces would cancel out and the answer would be 0 N of force, but your explanation indeed cleared my incorrect thinking and confusion. Thanks once again!

[ChaoticDsTroYeR]

Dude on Reddit just introduced me to a good teacher. W.

[umeshmidha]

Here after my physics classes, concepts further enhanced

[rymcmanus]

I think the root of people's confusion is that it's counterintuitive to say that a spring scale measuring 2 N has "a net force of 0". People assume the spring itself is responsible for counteracting the 2N of force in such a situation, rather than seeking an equilibrium to measure the external system.

[gregslingland]

This is useful, but highly counterintuitive. At least for me.

[TobyC]

Another guy here from Reddit. I read the explanations on reddit and was still confused, but watching this, the problem makes so much sense now.

[MrCrininer]

I'm here from Reddit, and you earned yourself a subscriber. Really well explained!

[stevenkiss]

Looking forward to more videos in the future. These help a lot with my fundamental understanding of physics.

[RootedHat]

If only my physics teachers had been this eloquent

[gamebuster]

I’m 34 and I learned something today, thank you

[ZombieDiesel]

This guy is on another level. Placing the book in front of the right side was genius

[Conceptofcandid]

Thanks for the audiovisual presentation

[jacobgrodman]

Crazy to see my high school physics teacher blowing up on a reddit thread 😂

[VancouverPallacy]

We are all here because of the reddit dude