FizziksGuy

You can do it one of two ways, the first with kinematics, the second by conservation of energy. I would assume no air resistance to make things simpler. If you choose the kinematics path, the following resources may help: Free Fall Video Free Fall Tutorial If you choose energy, check these out: Conservation of Energy Video Conservation of Energy Tutorial Good luck! (If you go with Kinematics, and choose down as the positive direction: v_i=12 d=40m a=9.8 m/s^2 Solve for v_f using vf^2=vi^2+2ad)

I love the last one!

Some more creative toilet paper physics can be found in a lab we did a few years ago (and may do again come review time...): http://aplusphysics.com/flux/aplusphysics/unrolling-toilet-paper/

Can you name five other examples of plasma? (A question I often give to my grad students in a plasma physics course?)

Wow, very cool! Are you planning on seeing the cathedrals someday? Which would you like to see first?

Wow, collisions, movies, rumbles and physics. It's all there! :saturn:

How long does it take the photons from the laser to get where you can observe them (assume a theoretical observer at your two points in space...)

How do we feel about plasma?

If you want to make 'em pretty... http://www.aplusphysics.com/forums/showthread.php?15-Embedding-formulas-into-your-posts Something like: MathType is a great program for creating math equations you can insert into most anything, or you can use the simple and free online LaTeX Equation Editor: http://www.codecogs.com/latex/eqneditor.php

On the right path!

Not sure I'd want what comes out when you 'piñata" the criminal...

A terrific video on the physics and safety of electrostatic discharges (ESD).

Having "engaged" in similar activities back when I was young and foolish, the real question is what happened when they got caught. And just for the record, trying to avoid the mess factor by having shopping cart ground-bungee drag races through hallways may result in ER visits and plaster. :einstein)

I think you've got it.

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For part a, I would use kinematics: d=vi*t+0.5*a*t^2, and then 300s*vf, and then the deceleration distance. For part b, the total force required, F=ma looks good, but make sure your mass is in kg.

Hi Matt. That looks correct. The total energy is conserved (neglecting friction) in this problem, so at the highest point it is at rest, KE=0, and all its energy is potential energy. As it falls, the potential energy gets converted to kinetic energy, so right before it hits the ground, its potential energy is 0, and its kinetic energy is 10kJ. Once it hits the ground and comes to rest, both potential and kinetic energy are zero (note that all of these are based on the assumption that we're calling the ground level our relative zero point of potential energy). :wave)

I like how you are taking the key concepts of the course and making them your own by developing your own rules and understandings. Keep it up!

Google is your friend... why not find out for your next blog post? To go even further, check out electrochromic lenses -- mighty cool!

Thrilled to announce that APlusPhysics has won the web redesign contest. Looking forward to seeing what the new design entails and sharing the results with you. Thanks so much for your support!

Very nice!

We have some exciting news! The free APlusPhysics website has been selected as a finalist in a contest to receive a free professional site redesign, but we need your help! Voting for the contest finalists is open now through Dec. 20, and we need all the help we can get. As a member of the APlusPhysics community, any help you can provide by voting and/or spreading the word would be greatly appreciated. You can vote by visiting the following link: https://www.facebook.com/LogoSnap/app_127709503932081 Thank you so much for your time and support. We're thrilled to continue bringing quality physics education materials to the public, and wish you and your families all the best this holiday season. Make it a great day! Sincerely, Dan Fullerton APlusPhysics.com

Great exploration Tony, and I'm thrilled you're enjoying my book! The readings on a scale are actually pretty tricky, and you've gotten a great start on understanding it. Let's start with metric scales. Typically metric scales have readings in kilograms, which is an inaccuracy. Scales read the normal force on an object (your weight, or the force of gravity pulls you down toward the center of the earth (mg). The normal force, aka the force of the scale, pushes back on you with the exact same force). So a scale reads force. Technically, it should be giving you a reading in Newtons. However, since most scales are used only on Earth, manufacturers have long since started putting the readings on the scale in kilograms (which, as you say, is the force in newtons divided by 9.8 m/s^2.) If you were to take the scale to the moon, it would be inaccurate, as it would show only 1/6th of your mass on the Earth, and mass doesn't change when you go to the moon. If it read in newtons, however, and showed 1/6th of your weight (in newtons), that would be correct. An American scale, on the other hand, typically gets it right in that it reads in pounds, which is a unit of force. On the downside, however, in the United States we do a miserable job of measuring mass correctly. We treat pounds (a force) as synonymous with mass, which it is not. In the English system, the correct unit of mass is the slug... and you hardly EVER hear anybody talking about a mass in slugs. Things get even trickier when you get to scales which accelerate (for example, put a scale in an elevator and watch its readings as it accelerates up and down). I had some students who put together a cool little video about it a few years ago... Thanks for the great feedback, and the great questions. You're definitely on the right track!!! Best Wishes, Dan Fullerton

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Very cool -- never heard of this before, but I'm going to have to dig a bit deeper!