# Quick Newton’s Laws Demo

Posted on: December 3, 2010

I was discussing Newton’s Laws and trying to explain how the tension increases in an elevator cable when it starts moving up.   The kids get it that the tension when it’s not moving is equal to the weight of the load, but once it starts moving, they get wacky.  Some seem to think the only weight at that point is the force from F=ma and the elevator is now weightless.

I put 1 kg mass on the large spring scale and showed how it pins the reading if I pull up.  They saw it, but it didn’t click.

On a whim a took I put the 1 kg mass and lifted it with some string.  My standard classroom string is macrame string from A. C. Moore.  It costs about \$3 for 1000 ft ball of string.  I think I go through a ball of it every year.  Anyway, the 10 N weight is nearing the limit of what the string can hold.  I accelerated the string upward just like I did with the scale and the string snapped.  Watch your toes, it fell to the floor and cracked a tile… oops.

Advertisements

### 1 Response to "Quick Newton’s Laws Demo"

This is a fantastic idea. Luckily for me, I have an elevator in my school so I take some analog bathroom scales and have the students video tape themselves (and the scale) when the accelerate up, move at a constant speed, and then accelerate down. It works out very nice…but your idea would be a great in class demonstration.

### What’s New in 2013/2014?

Every year brings a change, this one is no exception.

I will be picking up the sophomore honors Algebra II class to keep them separate from the juniors. This should help accelerate them and put them on a stronger track towards Calculus. Looks like there will be only one section each of Physics and Calculus, but still two of Robotics & Engineering.

Hot topics this year are going to be the Common-Core Standards, Standards-Based Grading (SBG), improving AP Calculus scores, and somehow adding Python, maybe as a club.

### Polls in the sidebar

Just a quick poll to help me understand who is stopping by my blog.

### Why not subscribe, it's free and I don't nag you about your clothes on the floor or the dishes in the sink.

If you are badly in need of more email or for some reason jonesing for a physics fix, enter your email address so I can bother you with my newest rant on science.

Join 314 other followers

### Blog Stats

• 1,299,589 hits by nerds like me since June 1, 2008
Advertisements