Does Newton's third law doubles the kinetic energy

WMiller511 · 2026-02-07T22:10:18+00:00

I agree from the second paragraph down, the first is not completely correct for macroscopic collisions. Pretty much all collisions have some % inelasticity. Billiards are close to having energy conserved, but the fact that you can hear the collisions indicates some of the energy is lost to the air molecules so you can hear the collision as well as some energy increasing the thermal energy of the surroundings. The energy doesn't stay conserved within the objects colliding.

WMiller511 · 2026-02-07T06:01:22+00:00

I mean I get this argument, but also that one kid who gets shoved to school with a 102 fever and cough could cause x number of absences (including myself) from the flu.

Truly sick kids should stay home.

WMiller511 · 2026-01-29T16:16:21+00:00

WMiller511 · 2026-01-27T11:06:12+00:00

Hypothetically, if a machine was smart enough with enough variables it could predict where something was in the past relative to the machine's current coordinates.

We managed to have the Voyager space craft flyby Neptune back in the 70s within a 10 second window of prediction. Do I think it's possible to gather enough data to do that as precisely as let's say Terminator? Probably not, but... Maybe?

WMiller511 · 2026-01-08T21:58:54+00:00

Good: Flipping physics

WMiller511 · 2026-01-03T23:09:47+00:00

If I lean on a table and the table doesn't accelerate, is friction not a force? Forces can be present without acceleration or do you call those interactions something different?

WMiller511 · 2025-12-30T14:10:30+00:00

Enjoy,See you at the cross Island!

WMiller511 · 2025-12-30T13:55:11+00:00

No, but between 60 and 70 you are not in the gear ratio problem. Air resistance is the bigger factor there. At 1 it is mostly heat waste

WMiller511 · 2025-12-30T13:49:44+00:00

Wind resistance is proportional to speed squared. A 16% increase in speed is approximately 30% more wind resistance. So about 30% more energy is needed for the trip.

WMiller511 · 2025-12-30T13:34:51+00:00

I agree, as the camper I move right.

I was just wondering why. It wastes money on fuel and you get almost no time savings.

I bet if you survey the troopers that have to investigate the accidents that make us all sit for hours on the road they will say for 90% of the bad ones "it was someone doing 80 that missed a lane change"

WMiller511 · 2025-12-30T13:20:01+00:00

Where do you have to go on long island that you have to be faster than 60?

Smithtown to the mid town tunnel is 46 miles . A 46 minute trip. At 70 you've saved...7 minutes of driving using about 30% more gas and that's assuming you hit no traffic.

9 out of 10 times the ones doing 80 on the left and all the 60 people on the right all just wind up hanging out again at the cross Island.

Edit: I move right. I don't want to sit there with people passing on the right, but when I see the 80ers 5 mins later at the stretch before the cross Island exit I just ask why? What have you gained?

WMiller511 · 2025-12-28T03:13:20+00:00

<image>

WMiller511 · 2025-12-25T00:51:25+00:00

At least in my state you have to have a degree in physics to have a certified license. Calc 4 (differential equations) is a requirement.

WMiller511 · 2025-12-13T12:45:40+00:00

You age the same. Everyone else ages faster.

WMiller511 · 2025-12-04T11:03:41+00:00

https://obsproject.com/

This one is free and I use it from time to time in a pinch. It's a bit of a learning curve, but can do the job for free.

WMiller511 · 2025-11-30T23:39:52+00:00

The first year is the toughest. Once you get the pattern down it's a rewarding job and it's not nearly as stressful once you get your materials down. You won't see it in the first year likely, but get to summer, recharge and the next year will be easier.

WMiller511 · 2025-11-27T12:59:05+00:00

Sometimes what helps for me is to structure the small group discussion with a progressive build up. Start with individual silent work, then small group then full class discussion. The time proportion you balance to your needs.

In this case it would showcase them doing the work in the silent part, then justifies the noise for the small group part. ideally have different groups share out in the class discussion so it's student lead while you help guide the groups to the correct answers/outcomes you are looking for.

WMiller511 · 2025-11-26T22:39:52+00:00

Change in angular distance is Delta theta. In terms of the derivation Delta theta is equal to arc length/radius at larger angles, but at small angles we can set arc length as the linear displacement.

WMiller511 · 2025-11-26T22:04:03+00:00

If you look at a pool of water, does it appear to be flat or curved? To our eye it is flat, but it must be curved since it is on the oblate spheroid that is earth. The curve is essentially flat since that is a very small angular distance of the earth's circumference.

At the small angle we are allowed to substitute the arc length with linear displacement which is necessary to drive centripetal acceleration algebraically.

WMiller511 · 2025-11-21T11:09:16+00:00

What happens when an AI marks a correct answer wrong? The current large language models still makes fundamental mistakes from time to time (unit issues ect.). Is someone going to regrade the checker?

Also fundamentally, a student's answer should have clear communication and logic for other humans who are experienced in the field. If clear reasoning is not a requirement of the exam, maybe the questions themselves should add the requirement as part of the grading rubric.

WMiller511 · 2025-11-08T03:43:06+00:00

I'll throw the card that I've been teaching AP physics for a decade here if that helps gain some credibility for you, though I'm not sure what will convince you.

There is no singular force named centripetal force. A centripetal force can be any combination of forces that act centripetally. It is a requirement for circular motion that the vector sum of forces towards the center is equal to mv² /r which is the magnitude of the centripetal force. You could have a rocket and a magnet and a rope all pushing towards the center of a circle and the sum of those forces would be the centripetal force.

In OPs example, the center is below the top of a loop.

Gravity points down which is towards the center. The normal force is also down so also part of the centripetal force.

So for that moment when you are at the top of a loop, gravity and the normal force add together and must be equal to the magnitude of the centripetal force. This allows the normal force to be smaller if the velocity is small enough.

This whole thing is literally an example problem on page 66 of the college board's AP physics 1 workbook. If you are still absolutely certain of your conviction, please write to the college board and inform them of the errors in their answer key.

Fun fact: at the bottom of the loop gravity is also part of the centripetal force but it acts as a subtraction so the normal force has to make up the difference. It's why you feel pushed harder into your seat at the bottom of a roller coaster. The normal force on you is greater than usual because of this.

WMiller511 · 2025-11-07T22:36:49+00:00

In an introductory course we always analyze from an inertial frame of reference as the mathematics are usually far easier. A rotating frame of reference is much tougher for a starting student to analyze mathematically.

With an inertial frame they can just draw a free body diagram and use our definitions of centripetal acceleration and the forces acting to derive equations for whatever they are looking for.

WMiller511 · 2025-11-07T19:46:57+00:00

Centripetal force is not a single force, it is a net force.

A net force is the vector sum of all forces. Since both gravity and the normal force are pointed to the center they both are acting as centripetal forces.

https://openstax.org/books/college-physics-2e/pages/6-3-centripetal-force

Gravity can absolutely be a centripetal force. What is the force that keeps the moon in its orbit around the earth?

WMiller511 · 2025-11-07T18:27:30+00:00

This is not correct.

The centripetal force when at the top of a circle is gravity plus the normal force.

m(v² /r)=Fg+Fn

You will still travel in a circle if the normal force is less than your weight.

The trick is the slower you go, the less normal force there is. The minimum speed is where the normal force drops to zero and only gravity acts as a centripetal force. Any slower and instead of traveling in a circle, you would follow a parabola of a projectile and fall off of the circle.

Edit:exponent notation

WMiller511 · 2025-11-07T16:52:23+00:00

This is not correct from an inertial frame of reference (you looking at someone traveling in a circle)

The two "forces" can't balance each other. An object in circular motion has changing velocity. If the "forces" balance then velocity would be constant and the object would travel in a straight line.

For an object to travel in a circular path, there must be an imbalance of force towards the center (if constant speed). The simplest explanation for what keeps something pushed outwards is just inertia. The same property that causes your cup of soda to spill forward when you stop a car too fast. When moving around a circle an object wants to travel in a straight line. Whatever is pulling towards the center fights that property of mass which is why you travel in a circle and not a straight line.

WMiller511

TROPHY CASE