Getting To Know ETS Physics Tests... Really Well

Posted by Antonio Levy on 5/27/15 11:00 AM

 

Much like Bill Murray in Groundhog Day, those who take many ETS physics tests may develop a feeling of déjà vu... 

ETS is many things: creative is not one of them. It uses the same questions over and over and over. Therefore, the best way to study for standardized tests of any kind (especially in physics) is to take lots of practice tests

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Tags: physics, GRE, physics SAT subject test

Inertia Experiments and Rolling Motion Part II

Posted by Patrick Callahan on 5/14/15 11:21 AM

Last time on our physics tutoring blog, we conducted an experiment to investigate the influence of the moment of inertia on rolling motion. We started with two objects that had the same shape, but very different size and mass. Starting from rest, we then set them both rolling down a ramp, to see which one would reach the bottom first. The objects had different values for the moment of inertia, but nonetheless reached the finish line at the same time. So, we resolved to try a second experiment, repeating the first experiment but with two objects that have different geometries. Again, to keep it simple, we’ll stay focused on objects that have a circular cross-section, and that are easily found lying around the house. This time, we’ll pit the marble against a roll of masking tape. The roll of tape is larger and heavier than the marble, but from the analysis of our previous experiment we might expect the mass and size not to influence the outcome. Let’s see what happens:

And they’re off! Here is the view from the starting line.

And here is a close-up of the finish line.

We have a winner! The marble beat the tape by a clear margin. So, the geometry of the rolling objects is definitely a deciding factor in this race. Let’s take a look at the math, and compare with the previous experiment. For the roll of tape, we can approximate the shape to be a ring, which has a moment of inertia of I = MR2 when rotated about its center. Using the subscript m to denote the marble and the subscript t to denote the roll of tape, we can set up the energy balance equations in the same way as we did before:

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Tags: physics

Inertia Experiments & Rolling Motion Part I

Posted by Patrick Callahan on 5/8/15 2:54 PM

Not that kind of inertia.

Sometimes, when you are sitting in a physics class staring at an intimidating wall of math, it can be easy to lose sight of the fact that the laws of physics originated as hypotheses to explain observations in the real world. Whether it was Newton getting bopped on the head by an apple, Galileo dropping stuff off the Tower of Pisa, or Franklin electrocuting himself with a kite, there was often an experiment that preceded and informed the mathematical formulation of a physical law. As a physics tutor in Cambridge, I find that it’s easier for my students to stomach the math if they’re able to imagine what it means, if they can figure out the physical consequence hidden behind the equation. For example, when looking at Newton’s second law (F = m a), I imagine pushing on a box. When I push (apply a force) on the box (a mass), it starts moving (it accelerates). If I push harder (apply a larger force) on the box (still the same mass), it starts moving more quickly (a larger acceleration). And while thought experiments are great, real experiments are more fun! Today we will set up some experiments to investigate one of the more abstract concepts in classical mechanics: the moment of inertia.

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Tags: physics

Physics Tutor: 3 Tricks for Physics Standardized Tests

Posted by Antonio Levy on 1/5/15 1:22 PM

Sometimes, you just do what you gotta do. 

Learning to take standardized physics exams, like the AP Physics exam or the SAT Physics Subject Test, is not unlike trying to become fluent in a foreign language. Both follow highly idiosyncratic logic and are best learned through practice. (And believe it or not, standardized physics exams have less to do with physics than physics aficionados would like.) Now before you combust, hear me out. I’m not saying that the tests don’t contain physics, or that understanding physics won’t help you; I’m saying that it is only one of many factors in these exams.

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Tags: physics, physics SAT subject test

Physics Tutor: Problem-Solving Tips II--Framing the Problem

Posted by Mike Goldman on 8/20/14 10:23 AM

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Tags: physics

Physics Tutor: Problem-Solving Tips II--Is Your Answer Reasonable?

Posted by Mike Goldman on 7/14/14 10:00 AM

 

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Tags: physics

Physics Tutor: How to Stick the Landing

Posted by Mike Goldman on 6/16/14 9:48 AM

 

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Physics Tutor: Analogies V--What makes Quantum Mechanics Quantum?

Posted by Mike Goldman on 5/28/14 11:42 AM

Conceptual picture of a photon, from physicsworld.com

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Tags: physics

The MCAT Tutor: Free Body Diagramming, Jedi-style

Posted by Jack the MCAT Slayer on 5/12/14 10:03 AM

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Tags: medical school admissions, physics, MCAT

Physics Tutor: Using Analogies IV (Let There Be Light!)

Posted by Mike Goldman on 4/16/14 10:02 AM

"Seeing the light" by Jenny Poole

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Tags: physics