Physics:

It Explains Everything

What is physics?

• Physics is the study of matter and energy

• It deals with how the two interact and interact with each other

• Chemistry is the study of matter but physics deals with the energy involved

You do physics every day

• Whenever you do anything, you’re doing physics

• Whenever you, as a body composed of matter, interact with another body of matter, you’re doing physics.

Here are some examples

We Will Keep it Simple

• Physics has many sub-divisions• Such as..• Kinematics

• cosmology

• quantum physics

• theoretical physics

• Condensed Matter Physics

• Atomic, molecular, and optical (AMO) Physics

• High Energy Physics

• Astrophysics

• Applied Physics

We Will stick to Kinematics

• This deals with motion on the large scale

• So we’ll be discussing things such as force, mass, weight, acceleration, Newton’s Laws, simple machines, speed, velocity, energy and energy transfer

• All of these topics should be familiar to you

• Let’s start with an easy one

What is a force?

• It is a push or a pull on an object (f =ma)

• there are only four forces in the known universe– gravity– electromagnetic force– strong nuclear force– weak nuclear force

• all forces that we see in nature are one of these four

Gravity

• This is the force of attraction between two objects

• It is determined by the masses of the two objects and the distance between them

• gravity explains the motion between large objects very well

• Large objects are considered things that are larger than the microscopic scale

– so we are large objects, insects, dust and the sun are as well

It is tricky though

• We really don’t know why or how gravity works

• We know how much gravitational force an object has

• we can predict its effect on another object

• we just don’t really know how it is generated or where it comes from

• But make no mistake, as it stands today, gravity IS NOT electromagnetic

Gravity at work

Strong Nuclear Force

• Lets talk atoms first• Atoms are composed of smaller subatomic particles called…

• Correct, protons, neutrons and electrons

• They usually contain the same number of electrons as they do protons

neutrons

• Neutrons are neutral, this means they have no electric charge

• But, neutrons do have mass• Protons and neutrons are packed together tightly in the atom’s…

• Correct, the nucleus• See…

The strong force weakens…

• …as the particles get farther apart• Soooooo……..huh?• Its like this• When protons are close together, they are attracted to each other.

• This short-range force of attraction is much stronger than the long-range force of repulsion

• So if they are far away from each other they will repel

SOMETHING LIKE THIS

STRONG FORCE

ELECTRIC FORCE

TOTAL FORCE

NO STRONG FORCE

ELECTRIC FORCE

TOTAL FORCE

SIZE MATTERS

• Atoms with small nuclei, such as hydrogen, are held together more tightly because the particles are close together

• This allows for the strong force to act on most if not all the particles

• If a nucleus is larger, such as in uranium, the strong force between particles can only act on other particles that are close to it

• It won’t act on those that are far away• But, the repulsive, electric force acts on all of them

• In many nuclei, the strong force is able to permanently keep the nucleus together

• These nuclei are stable• However if the strong force is not enough to hold the nucleus together, the nucleus decays

• This means it gives off matter and energy

• This “nuclear decay” is called radioactivity

LARGE NUCLEI WILL DECAY

• Large nuclei tend to be unstable• In fact all nuclei that contain more than 83 protons are radioactive

• Awesomely enough, many smaller ones are radioactive also

• Even some with only one or a few protons

• Thanks universe!

FUN FACT!

• Almost all elements with more than 92 protons DO NOT exist naturally on Earth.

• They have been produced in a lab

• They are so unstable that they decay almost immediately after they are made

That’s the most fun fact ever!

SCIENCE IS AWESOME!

Remember this?

STRONG FORCE

ELECTRIC FORCE

TOTAL FORCE

NO STRONG FORCE

ELECTRIC FORCE

TOTAL FORCE

The weak nuclear force

• Is the one responsible for the decay

• If the protons get too far away from each other the weak nuclear force pushes them apart and the atom decays

Let’s Talk Energy

• What is it?

• There are several definitions.

• This one is found in several textbooks:

• “The ability to do work”

• Okay, but what is the definition of work?

• If you don’t know, then this definition is useless

Here’s one that is better but pretty vague

• “Anything in the universe that is NOT matter.”

• Okay so this gives you half of infinity, not very helpful

Here is a good one...I mean it this time...well almost.

• But, to first understand energy we must understand matter. They go hand-in-hand ya’know.

• In fact, by Einstein’s definition, they’re the same thing E = mc2

• energy = mass times the speed of light squared• Plus, we find in nuclear reactions that matter and

energy are converted into each other...so they’re the same...I guess.

• But I digress

Matter

• Sometimes defined as “anything with mass that takes up space”

• Okay..but what is mass?• Mass is defined as “How much matter is in something”• So by this definition, matter is “anything that is matter

and takes up space”

• not very good. It is also defined as anything that is NOT energy. Or, the other half of infinity. Again, not very good.

Matter and energy

• These are the good definitions

• really

• for real this time

• really

• Matter: anything that can be detected with one or all of the five senses

• Energy: causes the movement and change of matter. CANNOT be detected with the five senses.

Energy comes in many forms...

• ...well kind of

• its actually all just...energy but since it does so many things and effects matter in many different ways it is easy to think of it as different types

• What are some of them?

Energy forms

• Light

• heat

• kinetic (1/2mv2)

• sound

• potential

Lets talk about potential energy

• It alone comes in many forms

• chemical potential– stored in the chemical bonds of molecules

• gravitational potential– energy stored due to an object’s position above

the surface of Earth (GPE = mgh)

• electric potential– energy of a stored electric charge

Law of Conservation of Energy

• Energy cannot be created or destroyed

• The amount of energy is constant in the universe

• it can change “forms” very easily but the amount never changes

So this......is this

...is this

...is this

...is this

...is this ...is this.

The Force/Energy Connection

• When a force is applied from one object to another, energy is transferred and converted from one form to another.

• All of the energy you use in a day came from the sun...ALL OF IT.

• How can that be true?

• Easy it just simply gets converted from solar energy to all the other forms

Energy back into the universe as light, heat, sound, chemical potential

Nuclear fusion reaction

photosynthesis

Cellular respiration

Force applied to log

Work

• The scientific definition of work is different than the everyday definition

• W = F x d

• or…work = force x distance

• This means that to actually do work one has to apply a force to something and move it in the direction of the force

Applying a force but NOT doing any work

Doing work

The force/energy/work connection

• Let’s tie it all together

• To move something, one must apply a force to it

• In doing so, energy is transferred from one object to another

• If the object moves, work was done on that object

• But it is possible to apply a force to something but NOT do work on it

Fun with math

• If you apply a 100 Newton force to a box, and you move the box 22 meters, how much work was done on the box?

• 2200

• 2200 what?

• The unit for work is the same as it is for energy

• so…2200 Joules or 2200 J

More About Force

• Of course the amount of force needed is directly proportional to the mass of the object

• What is a direct proportion?

• It means as the mass of the object increases the amount of force necessary to move it increases