Units

[PlatinumPenny]

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For those of you who have taken the MCAT or have serveral practice test under your belt, how important is knowing units (especially for physics). Like will there ever be two answer choices with the same number, but different units? Thanks!

 

[aevea]

Units are not that big of a deal. Occasionally, the MCAT will try to lead you to a math error from an overlooked k (kilo). The answer choices will all have the same units but one of the numbers would be what you would get if you forgot to convert. Units can also sometimes be useful in b.s.ing your way to an equation or constant.

 

[computerdorkdan]

Units are not that big of a deal.

Sorry, but I disagree. I think one of the best ways to understand physics problems is to know the units. If you follow your units you can't go wrong.

They do take a while to learn, but it'll pay off.

 

[FuSoYa]

I have to agree with Computer, knowing your units is very important and can help you answer otherwise difficult questions. there have been MCAT questions that ask specifically about units, and we all know that every question is important.

 

[Revilla]

Yes, sometimes you will get answers that are the same and the only difference is the units. Also, you will run into some questions you can answer simply by knowing your units. If the question asks for force and one of the answer choices is in J/s, you obviously know that's wrong. Likewise, if you're looking for joules and only one answer choice has N*m (or anything that could be a joule), you know it's right.

Know your units!

 

[SN2ed]

You should know your units. There are enough unit based problems that you need to be comfortable with them. If this is your weakness, take care of it. Plus, units are one of the easier weaknesses to overcome.

As previously mentioned, knowing your units and what they mean, can aid one's understanding.

 

[aevea]

Sorry, but I disagree. I think one of the best ways to understand physics problems is to know the units. If you follow your units you can't go wrong.

They do take a while to learn, but it'll pay off.

I have to agree with Computer, knowing your units is very important and can help you answer otherwise difficult questions. there have been MCAT questions that ask specifically about units, and we all know that every question is important.

You guys are right, my saying that units are no big deal was dangerously imprecise and sounded more dismissive/offhand than I meant it--I agree completely that units can be an important way to understand physics concepts and sometimes unit analysis directly counts for a couple of points.

What I want to say is that although units can be helpful, they're less important than understanding concepts and qualitative relationships between variables. Many MCAT physics questions ask "if you increase/decrease the value of one variable how will that affect the value of some other variable." In some cases analyzing the units and/or memorizing a bunch of equations can help you figure it out, but you need to be solid on the concepts to know when to use which relationships. For example, torque uses N*m which looks the same as the derived units for Work & Energy. But it's important to know that torque is a vector and should be treated more like force than like energy (i.e. the sum of the torques equals zero in equilibrium rather than the sum of the energies equals a constant).

Looking at the aamc practice tests, it seems like the importance of unit analysis has been de-emphasized along with quantitative analysis in the physical sciences section. PT 7-10 have significantly fewer questions where unit analysis pays directly than PT 3-6. So, my advice for PtPenny is: pay attention to the units as you study, they can be a useful means to an end, but focus on the concepts and the relationships between variables.

 

[physics junkie]

I remember using units a lot. They're not difficult to remember if you put them in context.

Energy = (1/2)mv^2 so you have (kg)(m/s)^2
momentum = mv so (kg)(m/s)
angular momentum = mvr so (kg)(m/s)(m)

It's not bad.