General > General Technical Chat
Load force vs. Effort force
Someone:
I'm guessing this is the level of complexity they are trying to convey. You can walk through with the student how equal/opposite means you can split the system through any plane/cross-section and there must be a balance.
SiliconWizard:
I'd be curious to see what kind of physics, even basic stuff, is being taught to 9-year olds anyway. I don't think I've ever been exposed to the concept of forces and pulleys until junior high school.
So if it's very basic stuff, I wouldn't worry about the exact terms anyway. As much as I don't like teachers messing up with terms, we need to remember those are just classes for 9-year old kids.
edy:
I just realized I completely goofed up on that lifting table question by IanB. The truth is if I apply a 9.80001 N force continuously the 1 kg weight doesn’t just go up… it accelerates up! This is a better analogy…
Imagine a balance, perfect frictionless. A 1 kg weight on each side of the balance, each pushes down exactly by 9.8 N and the balance pushes up also by 9.8 N so things don’t move, they are stationary. If you want you can use a pulley with 2 weights, same idea. You come by and ever so slightly give a nudge to one side… say 0.00001 N for a split second, enough that it creates an acceleration, then you take your finger away… no more acceleration but the balance (or pulley system) is now moving at a constant rate of speed. One side of the balance goes up, other side goes down. Or if thinking pulley, like elevator and counter-weight.
Now it could take 1 year to move 1 meter, it doesn’t really matter. The point is that it took a tiny effort to get things in motion. The increase in potential energy on one weight is balanced by the loss of potential energy of the other weight.
Now imagine a 1 kg drone hovering and thrust of 9.8 N down. It is not moving. I come by and nudge it with my finger… it starts to move up. My finger produces an acceleration but the minute I remove my finger the drone has constant linear motion, constant speed, because force of gravity exactly cancelled by thrust force of 9.8 N. It will continue to move up until I stop it again with my finger. This could be 1 minute later or 1 hour later (I am of course not limiting the case by anything real here like battery life, wind, etc).
Whether it takes 1 minute or 1 hour, if the drone moves up by 1 meter in each case we have the same situation of increase in potential energy (relative to the gravity well of Earth).. Sure we used 60x more battery energy to keep it hovering against gravity for 1 hour vs 1 minute, but the initial “nudge” that kicked the drone up ever so slightly was what actually moved the drone. So again this is an integration of net force vectors over time which produces the F=ma that then affects position of drone/weight. Sounds like accelerometer-based movement tracking.
Anyways thanks for all the input… you know the saying, the “teacher learns more from the student”. Having another look at this stuff years later I appreciate even more of the nuances that I probably glossed over while going through it.
RJSV:
Yeah... Just like you (,just did), GLOSSED OVER, the concept...FRICTION.
YEAH, NO, virtually none of that is going to happen.
I'm now 'nudging' myself, to move, ever so slowly, I'm declaring it doesn't matter how slow...
I'm just moving away, ...and will STILL be moving, from that NUDGE, like, wasn't that like 6 hours ago ?
james_s:
--- Quote from: IanB on April 01, 2022, 06:33:11 pm ---I can see how you might react that way, but being serious, learning has to be pitched at the level of the student.
For example, when I was 10 years old, I observed by experiment that a loudspeaker had a lower volume when connected with thin wires than when connected with thick wires. I asked a teacher why that might be, and he told me that maybe electricity has a harder time flowing through the thin wires, and that maybe it gets impeded somehow and that's why the volume is lower? I remember not really buying that argument, because to me a wire was a wire, and the size of the wire shouldn't matter to the flow of electricity.
We have to remember that some things are not really easy to understand at 9 or 10 years old, and there is no point getting too technical before students have enough knowledge to appreciate the details.
--- End quote ---
I certainly had a stronger understanding than that when I was 10. I didn't know the math, but I did understand the concept of resistance and higher current requiring a heavier wire. It was very intuitive to me, a garden hose could move a lot more water than a drinking straw. I was also familiar with the idea that you can't get more energy out of a system than you put in. My dad was an engineer and my uncle an electrician and I was fascinated with that stuff.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version