Physics For Dummies

Because the difference between CGS and MKS is almost always a factor of 100, converting between the two systems is easy. For example, if you know that a ball drops 5 meters, but you need the distance in centimeters, you just multiply by 100 centimeters/1 meter to get your answer: 100 centimeters

5.0 meters #

= 500 centimeters

1 meter

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Note that because there are 24 hours in a day, the conversion factor equals exactly 1, as all conversion factors must. So, when you multiply 1,560 miles/

day by this conversion factor, you’re not changing anything — all you’re doing is multiplying by 1.

When you cancel out days and multiply across the fractions, you get the answer you’ve been searching for:

,

1 560 miles

1 day

65 miles

#

=

day

24 hours

hour

So, your average speed is 65 miles per hour, which is pretty fast considering that this problem assumes you’ve been driving continuously for three days

Always remember to stick with the same measurement system all the way through the problem. If you start out in the MKS system, stay with it. If you don’t, your answer will be a meaningless hodgepodge, because you’re switch-ing measuring sticks for multiple items as you try to arrive at a single answer.

Always keep in mind that the real world comes first and the math comes later. When you face a physics problem, make sure you don’t get lost in the math; keep a global perspective about what’s going on in the problem, because doing so will help you stay in control.

As time goes on, those models start getting numeric, which is where physics students sometimes start having problems. Physics class would be a cinch if you could simply say, “That cart is going to roll down that hill, and as it gets toward the bottom, it’s going to roll faster and faster.” But the story is more involved than that — not only can you say that the cart is going to go faster, but in exerting your mastery over the physical world, you can also say how much faster it will go

Many people are a little on edge when they think about physics. It’s easy to feel intimidated by the subject, thinking it seems like some foreign high-brow topic that pulls numbers and rules out of thin air. But the truth is that physics exists to help you make sense of the world. It’s a human adventure, undertaken on behalf of everyone, into the way the world works

Describing motion and how it works is the first step in really understanding physics, which is all about observations and measurements and making mental and mathematical models based on those observations and measurements. This process is unfamiliar to most people, which is where this book comes in

Some of the most fundamental questions you may have about the world deal with objects in motion. Will that boulder rolling toward you slow down? How fast will you have to move to get out of its way? (Hang on just a moment while I get out my calculator . . .) Motion was one of the earliest explorations of physics, and physics has proved great at coming up with answers.

You can observe plenty going on around you all the time in the middle of your complex world. Leaves are waving, the sun is shining, the stars are twinkling, light bulbs are glowing, cars are moving, computer printers are printing

Physics has been around as long as people have tried to make sense of their world. The word “physics” is derived from the Greek word “physika,” which means “natural things