springs

DIY Force probe

I was thinking about some experiments that deal with friction and I wanted to show something with a force probe. The problem is that most people don't have one of these. So, I decided to try and make one out of simple things. In this case, I am using some straws, a rubber band and some paper clips. Let me draw a little sketch of how this thing works. The basic idea is to use the rubber band to measure the force (by measuring the amount the rubber band stretches). The two paper clips do two things. First, it allows you to hook up the device to something (like hanging some Lego bricks on…

What happens when your kids won't give you a turn on the Wii? Simple. You take their LEGO bricks and their slinky and do some physics. I will keep this simple. Basically, I created a slinky holder out of LEGO pieces and added LEGO bricks to the end to stretch it. Here is the video. Lego + Slinky = Physics from Rhett Allain on Vimeo. Maybe in an un-Dot Physics fashion, I am not going to analyze this data. I am not going to even describe the physics. Instead, I will leave this as a What Can You Do With This in the style of Dan Meyer. I will give a couple of hints. First, I put this on…

Pendulum - a third way

Looking back at part I of this idea, I don't think I did a very good job. Let me summarize the key things I wanted to say: Normally, there are two ways of modeling the motion of an object: Calculating the forces on the object and using the momentum principle or Newton's second law (which are the same thing). I called this the Newtonian way. The problem with this method is forces that constrain the motion (like the normal force). These forces have a variable magnitude to make the object stay on a particular surface. Defining some variables that describe the system as it is constrained.…

Accelerometer Version-2

So, I built a new accelerometer. Why? The jelly-jar one was just not doing it for me. Plus, the cork was starting to make the water all yellowy. It was a good start, but I can do better. What was wrong with the jelly-jar one? First, it didn't let the cork move very far before hitting the wall. Second, it was kind of hard to see exactly where the cork was. Lastly, there was no way to get a reading of the acceleration from the jelly-jar. Now, I am going to fix that. My new design uses a sphericalish glass flask. The floating bob is anchored in (near) the center of this sphere. Here…

Accelerometers - and build one yourself

This has been on my list for quite some time. Really, it must be since i posted about measuring acceleration in free fall with an iphone. So, this post will be all about accelerometers. How does an accelerometer work? Really, an accelerometer measures force some way on a known mass. Let me show an extremely simple accelerometer - a mass on a spring. (image from Science Buddies where they have instructions on building such a device) Suppose I put this accelerometer in a stationary and non-accelerating elevator. Let me draw a free body diagram for the mass on the end. No magic here, right…

More Examples of 'Weightlessness'

Jennifer over at Cocktail Party Physics has a nice post about her trip to Disneyland. The one ride that would be fun to play with (in terms of physics) would be the tower of terror. Think of the cool things you could do with a video camera during that ride. It would be like a mini-vomit-comet. Anyway, I want to talk about one part of Jennifer's post. "As one would expect, this lifted us out of our seats slightly, as much as the straps would allow, and we got that one glorious moment of seeming weightlessness, before reaching a jerky stop and being raised back up for another drop." It is…

Water Stick springs in Fantastic Contraption (the game)

Here is what is cool about [Fantastic Contraption](http://fantasticcontraption.com/) - it's like a whole new world, a world ready for exploring. I am Newton, and I can see if this world follows the models that I propose. In this post, I am going to explore the elastic nature of the "water-sticks". If you have played fantastic contraption, I am sure you noticed that the water-sticks are springy. How does these springy sticks work? Are they just like the springs we have in the real world? An excellent model for springs in the real world is Hooke's law. It says the force exerted by a…

Spring Motion and Numerical Calculations

Maybe you know I like numerical calculations, well I do. I think they are swell. [VPython](http://vpython.org) is my tool of choice. In the post [Basics: Numerical Calculations](http://scienceblogs.com/dotphysics/2008/10/basics-numerical-calculation…) I used vpython and excel to do something simple. I will do that again today (in that this problem could also be solved analytically). However, there is one big difference. This problem has a non-constant forces. Suppose I have a mass that is connected by a spring to a wall. This mass-spring is sitting on a table with no friction. ![…

Fake vs. Real Forces

In this post, I am going to talk about real and not real forces as well as the fake centrifugal force (if you don't like the word "fake" you could replace that with "fictitious") First, an example: suppose you are in a car at rest and press the gas pedal all the way down causing the car to accelerate. What does this feel like? If I weren't skilled in the art of physics, I might draw a diagram something like this: ![Screenshot 20](http://scienceblogs.com/dotphysics/wp-content/uploads/2008/10/screensho…) Yes, maybe someone would add gravity and the chair pushing up, but this shows the…

Resonance and a Magic Trick

Magic tricks are cool. Especially when the trick is really physics. In this trick, I can make one of the four balls move more than the others. (When you watch the video, you will see why I am not a professional magician). You could set this up in a variety of ways. I state that if we (me and people around me) all work together with our mind and focus on the same ball, our brain waves can resonate with that ball and make it move. I let the people around me pick. In this video, I make the smallest two move. So, what is the trick? The trick is not a trick. It is not resonance with brain…