welcome to physics 100 adults were shown this picture of a school bus: and asked, “which way is it...

Welcome to Physics

100 adults were shown this picture of a school bus:

and asked, “which way is it moving?” – there are only two choices:

to the right or to the left.

While some got the answer right, most admitted that their answer was just a guess.

The same picture and question was presented to 100 pre-schoolers.

Nearly everyone got the answer right.

How is that possible?

In every way we can measure, the adults are “smarter” than the kids, yet they could not solve this simple problem.

This is the basis of why we teach physics –

although practically no one realizes it.

One of our primary objectives – in this course – is to help you organize your view of the world.

So, Which Way?

Left Right

?

First, some misunderstandings

One is that a lot of people believe...

physics is just common sense.

Do you?

Let's look at some Common Sense.

True or False?

1. Under normal conditions, the electricity in your home is perfectly harmless -

even if you touch exposed wires.

2. If a penny fell from the top of the Empire State Building and hit you on the

head, you could be very seriously injured ‑ maybe even killed!

3. Objects have no weight in a vacuum.

4. Astronauts in the space shuttle float around because of a lack of gravity.

5. If you could scale an ant to the size of an elephant, it would be incredibly strong.

6. Generally, light things float in water while heavy things sink.

7. There are so many asteroids in the belt between Mars and Jupiter, spacecraft have to be carefully guided to avoid

running into or being hit by one.

8. The speed of light is a universal constant (always goes at the same speed).

9. In ancient times, alchemists tried to convert lead to gold. They failed because

it cannot be done.

10. If you are 6 feet tall and want to see the reflection of your entire body, you will need a mirror at least 6 feet tall or you will have to stand back from a smaller one.

11. A bullet fired from a powerful gun carries a lot of force with it.

Which is it?

12. We all know (I hope!) that light travels faster than sound.

But how many times faster?

A. 100

B. 1000

C. 100,000

D. a million

13. The air in this room weighs

A. Less than 1 ounce

B. between an ounce and a pound

C. between 1 pound and 10 pounds

D. more than 10 pounds

E. more than 100 pounds!

14. Which is hotter (higher temperature),

A. the wooden top of your desk

B. the metal legs of your desk

C. neither - they are both at the same temperature

15. On a very clear night, far away from city lights, the number of stars you could see would be

A. a few hundred

B. a few thousand

C. hundreds of thousands

D. millions

E. billions and billions

16. Which temperature scale is part of the metric system?

A. Fahrenheit

B. Kelvin

C. Celsius

D. none of the above

Common Sense

"The sum of your experiences to age 18".

- Albert Einstein

What do you think?

Of all the things physics is, one of the most important things you MUST learn is what it is not.

It is not common sense.

But then,

WHAT IS IT?

There are Three Fundamental Sciences:

BiologyStudy of life

ChemistryStudy of matter

PhysicsStudy of motion

So Physics is about motion…

the causes of motion

the effects of motion

the analysis of motion

In a sense, it is about the Facts & RulesThat govern motion

Some motion is pretty easy to see and comprehend (the answer can be seen).

Some is impossible to see and difficult to understand (the answer cannot be seen).

But

ALL MOTION follows the same set of rules

Everywhere - All the time - No exceptions

A Lot of Rules?

No, actually, there are remarkably

few

and if you think about it,

they have to be pretty simple.

And, it is much easier to learn a rule

than to memorize all the applications of it.

You could memorize every temperature on the Fahrenheit scale,

and the corresponding Celsius values...

or, you could learn

5F - 9C = 160

Some folks even think that Physics is just a collection of rules and facts...

some easy ones like these:

(net) F(net)if = 0 then ΔMotion = 0

net

netF

Fif 0 then m=

a

net netif F then F+,+,+,+,+,+,+,+,+,+,+,+,+,+,

E A dq

0

B A d 0

E dd

dtB

B d Id

dtE

0 0 0

God said

and there was Light

We'll Study

Energy

Sound

Light

Electricity

and other neat stuff.

We Will Learn (and understand)…

Which hits the ground first, a bullet fired from a gun or one just dropped?

What keeps a satellite from falling to the earth - or racing off into outer space?

Which will skid to a stop faster, an empty truck or an identical truck with a heavy load?

How can you walk on a bed of red-hot coals without getting burnt?

Why is it cooler on the top of a mountain?

How old are the atoms in your body?

Why is the sky blue?

What color is the sun?

At Noon? At Sunset? In space?

But it all boils down to motion

– at some level – somewhere.

The First Thing we MUST learn is this:

Physics is Simple

but it isn't Easy

HOWEVER…

The most incomprehensible thing

about the universe is

that it is entirely

comprehensible.

…A. Einstein

The Tools of Our Trade

Before we can begin the study of physics, we need to review and discuss:

Mathematics

Scientific Notation

Units: SI and MKS

Conversions

MATHEMATICS

ARITHMETIC

Add (2 + 2 = 4)

Subtract (4 - 2 = 2)

Multiply (2 x 4 = 8)

Divide (8/2 = 4)

Do Powers (23 = 8)

ALGEBRA

Simplification of formula

You must be able to do this:

Lfor gL2π t:Solve

About algebra…

Look…Algebra is the "language" of physics. I cannot over emphasize the following:

You should be able to go from:

2

2

t gL =

4toLt = 2 g

If you can't, you NEED to see me.

Expressing your Answers

This is always a concern, so let's say this…

Round off your answers to the point where they make sense.

For example, if you divide 30 by 7, your calculator will give you

4.285714286

No one needs that kind of precisions, so it makes sense to just round

4.285714286

off to something like

4.29 or even, maybe 4.3

ON THE OTHER HAND

If you are comparing two numbers, like

9.812 m/s2

and

9.843 m/s2

it would NOT make sense to round both off to 9.8 m/s2 because that would make them both look the same,

and clearly they are not the same.

9.812 m/s2 and

9.843 m/s2

can either be left as is or, rounded off to

9.81 m/s2 and

9.84 m/s2

either choice makes sense.

Scientific Notation

Makes dealing with large and small numbers much easier.

Numbers are expressed by a single digit to the left of the decimal.

0.000000004 becomes 4 x 10-9

20,000,000,000 becomes 2 x 1010

UNITS: SI and MKS

Back in the day, we used the term MKS which stood for

MetersKilogramsSeconds

Now we use the term SI (Systemé Internationalé)

Here are the big 3:

Length: meter (m)

Mass: kilogram (kg)

Time: second (s)

We use these units because other units (such as Newtons) are based on them.

Expressions like F = ma (Newton's 2nd Law), wouldn't make any sense if you used

grams instead of kilograms,

or centimeters instead of meters,

If you do,

YOUR ANSWERS WILL BE WRONG

In some cases, standard units are too big or small to be practical.

For larger or smaller quantities, we add or drop prefixes. The most common are:

grams instead of kilograms

centimeters or millimeters instead of meters

BUTExcept for very specific exceptions

ALWAYS

express answers in meters, kilograms and seconds, or,

YOUR ANSWERS WILL BE WRONG

CONVERSIONS

You MUST be able to do the following:

Convert length measurements to meters

Convert mass measurements to kilograms

Convert time measurements to seconds

THEREFORE...

You will NEED to know, for example,

How many meters in a centimeter

How many kilograms in a gram

How many seconds in a minute

AND...

You need to make conversions BOTH ways.

There are 100 centimeters in 1 meter,

and,

there are .01 meters in a centimeter.

Unfortunately...

It is unlikely that I will be of much help to you, so,

YOU MUST KNOW HOW TO DO THESE CONVERSIONS

ALL BY YOURSELF

CW 1 - Mathematics