Physics

Introduction to physics basics and kinematics

Things you should already know

Significant figures (although we will not use them in this class )

Metric system conversions (we will use these daily)

Greek alphabet/symbols (we will use these daily as well)

This information will not be “covered” in class. However, it will come up on a daily basis

You are responsible for knowing this information

There will be refresher links available on the website if needed and some conversions and symbol help on the first page of you homework

Motion the change in position and/or orientation of an object.

All motion is relative that is all objects move w/r/t other objects.

in order to describe the motion of an object it must be compared to another object.

 

How do we describe motion?

Question? Are you moving?

Question? Are you moving?

Answers may vary. If you are thinking about whether you are moving with reference to (w/r/t) your

desk……..then no you are not moving

HOWEVER………. If you are thinking about whether you are moving with reference to the sun……….then you are

in fact moving because (the Earth is moving around the sun and you are on the Earth, therefore you are moving)!

Introduction to Kinematics

Kinematics the study of HOW things move.This encompasses things like speed, velocity

and accelerationDynamics the study of WHY things move

This encompasses things like forces and energy

Position the separation between an object and some reference point. 

Distance (d, s, r) a scalar quantity describing the total path length. “how far did you actually travel?” think about miles added to the odometer

 Displacement (x, y, d, s, r) a vector quantity describing the straight

line path length between two points. “how far are you from where you started”

 Examples: running around a track, road trip (total mileage vs. straight line distance), football

Distance vs Displacement

The red line is the distance you traveled. Your odometer would possibly read something like 8 miles

START

Stop

Distance vs Displacement

The blue line is the distance you traveled. Your odometer would possibly read something like 8 miles

The green line is the displacement. It is the straight line path (and it associated magnitude) from where you started to where you finished

START

Stop

Scaler vs Vector Quantities

Scaler – quantities that only have a magnitude (number/size) associated with them Speed (5.2 m/s)

Distance (24m)

mass (98 kg)

temperature (37 C)

Time (30 sec)

Vector – quantities that have a magnitude and direction Velocity (5.2m/s East)

Displacement (24m west)

Acceleration (9.8m/s2 down) Force (20 N Right)

SPEED

Speed (s) the speed of an object is the rate at which a distance is covered in a time period.

Notice because speed involves the scaler distance quantity this also makes speed a scaler quantity. It is common to also use the v symbol for speed. Furher explanation to follow in proceding slides

Average speed ( s ) -the average speed of an object is the rate at which a (total) distance is covered in a (total) time period.

t

ds

t

ds

*Σ = the Greek symbol sigma meaning sum of. It is common to drop the both sigma when writing this equation. Again, it is common to also use the v symbol for speed. Further explanation to follow in proceding slides

Velocity

Average velocity ( v ) -the average velocity of an object is the rate at which a (total) displacement is covered in a (total) time period.

.

Again, it is common to drop the both sigma when writing this equation and use your brain to remember you need the total displacement and time. IT IS ALSO COMMON TO REPLACE THE x SYMBOL WITH THE d SYMBOL AND AGAIN TO USE YOUR BRAIN TO KNOW WHEN YOU NEED TO USE DISPLACEMENT AND WHEN TO USE DISTANCE

velocity (v) the velocity of an object is the rate at which a displacement is covered in a time period.

Notice because velocity involves the vector displacement quantity this also makes velocity a vector quantity….meaning the final answer needs both a magnitude (number) and direction

t

xv

t

xv

Summary of Equations (and possible substitutions)

Since the s symbol and the v symbol are interchangeable (you must USE YOUR BRAIN to determine what quantities [distance or displacement] are necessary) and the x symbol and d symbol are interchangeable the entire equation for average speed/velocity can look like this:

Also remember that it is common to drop the sigma (Σ) and the final equation looks like this: (this is the first of our BIG FIVE equations you will be using over and over and over and over and over and over and …..you get the point

vt

x

t

ds

t

dv

Instantaneous Speed or Instantaneous Velocity

Average speed/velocity considers the TOTAL distance/displacement traveled in a TOTAL TIME frame. Instantaneous speed/velocity is the rate at ONE SPECIFIC MOMENT.

Specifically the instantaneous speed/velocity is the rate of change in distance/displacement as the time frame approaches zero ( )

Would your speedometer indicate your average speed or your instantaneous speed?

want the answer??? CHECK THIS OUT

t

ds

t

0

lim

We will start applying the information in this powerpoint in class after the domino lab and the application may help you to better understand. If this all blows you mind and you are still very confused and worried . CHECK THIS OUT :)

“I learned very early the difference between knowing the name of something and knowing something.” ― Richard Feynman