Intro to physics part 1: Motion (an attempt to educate)

Hello there ats and welcome to the first and hopefully the start of mini series of posts attempting to teach the basics of physics. I am by no means a pro, this is the first time I’ve really ever done anything like this, aside from teaching a friend a or two, so I don’t expect it to be the best but I do believe it will be good for this site. I’m going to try to stay clear of as much high level math as possible, in order to give everyone a chance to learn. If you would like more math involved let me know. I will also post problems for people to solve if wanted as well. If anyone wants to maybe team up with me I wouldn't mind that either.

I have only borrowed the definitions and equations to explain, everything else is my writing and way of explaining.

Intro to physics part 1: Motion

Before we start I want to give a list of the variables we will be using so I don't have to explain during every segment.
v=velocity
x=distance
a=acceleration
s=displacement
Δ= A change in (Δ is known as the greek alphabet letter Delta)

Motion
Motion is the action or process of moving or of changing place or position; movement. Motion was one of the earliest studies in physics and without what we know about motion now the world could have been a different place. Motion involves everything we will cover in this, which is quite a bit so lets get started.

Displacement
A displacement is the shortest distance from the initial and final positions of a point P. It can be the length of an imaginary straight path, typically distinct from the path actually travelled or it can be as simple as this scenario.
You are standing at a spot you turn east and walk 3 ft. You then turn around and walk 10ft west. From your original starting point you have travelled a distance with a displacement equal to 3ft-10ft which of course equals -7ft. Displacement can produce both positive and negative answers.In physics displacement is usually shown as the variable (s). Displacement is what is known as a vector, which is a quantity, such as velocity, completely specified by a magnitude and a direction. There are different equations for displacement in different scenarios such as linear motion and non linear motion which we will come back to later.



Speed, Velocity and Acceleration.
Assuming those reading this already know what these are I will skip defining them. Speed=distance/time

Speed is only a magnitude without a given direction therefore you will see velocity (v) used a lot more as it defines an object in motion, travelling in a direction. With this being said we can rewrite our equation as follows: v=Δx/Δt or (Velocity= change in distance / change in time or v=(xf-x0) / (tf-t0)

I like to write the equations out in each way because some people are more comfortable reading it some ways more than others.
When referring to non uniform motion Δv=vf-v0


Eventually you will be asked for certain speeds rather than an overall speed. Average, uniform and instantaneous speeds are what I am referring to. None of these are the slightest bit difficult to figure out but it is good to know differences and how to get your answers.

Instantaneous Speed is your exact speed at any given moment. If you are driving and you happen to look at your tachometer or if you happen to pass a police radar that lets you know your speed and it says 65mph, your instantaneous speed is 65mph. Uniform speed refers to a constant speed.

Figuring out your average speed is a bit more work than these but still pretty easy. Let’s say you travelled 1000 miles in 3 days. To find your average speed in mph you would first take 1000 and divide by 3, which is equal to 333.33 miles per day. In order to get to per hour and not day we instead multiply (1000/3) by (1/24), which is 1000/72, which is roughly 13.88 mph.

Acceleration, which I'm sure most of you know, is any change in velocity whether it be an increase or a decrease.

The equation used for finding acceleration is a=Δv/Δt or a=(vf-v0) / (tf-t0)
Acceleration is characterized by units such as mph, mps and so on. In order to calculate units of acceleration use distance/time (squared).

Acceleration, just like velocity and speed, can also be measured as an average or instantaneous answers as well.
In order to find the average acceleration we just use the equation
ā = (vf-v0) / (tf-t0)
The variable ā = Average acceleration.

With all we have covered so far you can now find a way to relate these and solve equations with given information. I want to stop here because it will be easier for me to group the next few things together and leave these as are. The way my teacher taught this was he basically gave us the info here and left it up to us to figure out how to switch them around to figure out how to solve different problems.

I’m done for now though as I really want to see what people think.

PLEASE tell me what you guys think. I know this was somewhat brief but if you guys think this could be something worth continuing I will make sure to make them worth it.

If enough people enjoy, I will start the next part right where I left off. I will explain some of the more advanced equations you can form with info given here and I will have practice problems and such to further explain. For now you guys can go look online for some problems.

Part 2 would also include a more detailed look at vectors, Newton's laws explained in depth, momentum, angular momentum, laws of orbit, gravitational pull and collisions. Which would pretty much finish up motion so I would go to thermodynamics after.

-Seangkt


[edit on 14-4-2010 by seangkt]

reply to post by seangkt


Is there a conspiracy angle to any of this?
Just wondering if I missed it.

All the equations are good and fine, but sometimes you have to break free from the box, even in physics there is a box that ties you to certain 'laws.'

Reach farther and you'll find more, with less headaches!

Just a minor point, but acceleration is a change in velocity, not speed. Acceleration and velocity have vector componets, speed doesn't. If you change direction without changing speed you have still accelerated.

Originally posted by Sparky63
reply to post by seangkt

 

Is there a conspiracy angle to any of this?
Just wondering if I missed it.

Well some people seem to think there is. This is Newtonian physics, and Einstein came along and proved this math works in some cases (non-relativistic velocities) but not others (relativistic velocities, for example), but some people think Einstein is wrong and it's a conspiracy to make everyone think Einstein was right.

My own personal guess is, just like Einstein came along and tweaked Newton's math without invalidating it completely, someone will also probably come along and tweak Einstein's math similarly without completely invalidating it.

Originally posted by blujay
All the equations are good and fine, but sometimes you have to break free from the box, even in physics there is a box that ties you to certain 'laws.'

Reach farther and you'll find more, with less headaches!

Sometimes in physics yes out of the box is good. These however are the "laws" of motion. There is no outside the box when it comes to laws. Laws are infallible unlike a theory.

The laws of motion and thermodynamics are 2 of the most rock solid things we no about in science.

Effort appreciated OP. . . Looking forward to your next installment

One more to add for you:

Jerk (yes, it is really called this) is the rate of change of acceleration. The idea is just like how acceleration itself is the rate of change of velocity, as was already said.

Originally posted by DragonsDemesne
Jerk (yes, it is really called this) is the rate of change of acceleration.

I'm not a rocket scientist but I'm guessing that as the fuel in a rocket is consumed, the thrust to weight ratio increases and therefore so does the acceleration, so this would probably be common in rocket launches.

Youd be hard up giving a physis lecture here. There are so many text books free in libraris. If people dont want to learn, they wont.

[edit on 14-4-2010 by polarwarrior]