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Introduction To Physics

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Title: Introduction To Physics


1
Introduction To Physics!
Discussing the concepts of
  • Force
  • Work
  • Inertia (Newtons
  • 1st Law)

2
1 FORCE
Whats happening to this bobsled?
Youd probably say that its being pushed forward.
Yeah, its definitely being pulled along.
3
2 So well define force
ALL of these FORCES can be described as a PUSH or
PULL
FORCE a push or pull
Here are some examples
4
3 So, in our classroom
What forces can we identify?
  • In fact, there are so many body processes
    controlled
  • by muscles pushing in your body, (breathing,
    moving
  • blood, digesting food, pulling your bones, etc)
    that
  • well just move on from the body.

5
4 Is that all?
Not even close.
If we get picky, we can consider minor things
like the weight of earrings pulling on earlobes.
Every time one of the millions of bacteria in the
room land on something, they give it a tiny
little push.
Your booty is pushing on your seat and your
feet (hopefully) are pushing on the floor. The
seat and floor, in return, are pushing right back
on your body, holding you up.
6
5 If we REALLY wanted toget picky
each of the TRILLIONS of atoms that make up ALL
of the stuff in this room is held together by the
most powerful forces we know of
NUCLEAR forces
So, its obvious that forces are everywhere in
our lives, and many actually allow us to live!
7
6 More with force
Forces come in different amounts. Youd
much rather be punched by your little sister than
this guy
We measure forces using the unit Newton.
Newton is abbreviated with a capital N.
  • 3 miles 3 mi
  • 4 gallons 4 g
  • 2.4 liters 2.4 L
  • 5 Newtons 5 N

FYIa Newton isnt very much. It takes about 4.5
N to equal a pound of force.
8
7 So, summarizing force
A force is a push or a pull.
We measure force using the unit Newton (N).
We could use other units for force, such as
pound, but people in other countries wouldnt
understand that as well. I weigh about 850 N.
9
8 Allow me to introduce
THE KING OF FORCE!
No, not him.
Close, but no cigar.
THE PRINCE OF INERTIA!
THE GREATEST SCIENTIST EVER!
No, DEFINITELY not him.
This guy with the goofy wig
10
9 Whats so special about this dude?
His achievements in INVENTING a type of
math (some of you will take it in high
schoolcalculus) is important enough. But his
work in science was far more astonishing.
Newton basically used knowledge gained from
his heroes (like Galileo!) to explain to us how
why things move in the universe.
When you can describe a concept like WHY
THINGS MOVE in 3 short little LAWS, youre gonna
go down in history.
11
10 So were gonna have to learn his Laws this
year?
Nah, just his 1st Law, really, and thatll be a
few days from now.
But we can at least try to put into English his
sorta confusing laws and see what he was getting
at.
Heres my one-sentence summary of his 1st law IT
TAKES A FORCE TO CHANGE AN OBJECTS MOTION
and he used a term that has stuck with us
since inertia
12
11 Thats pretty much just common sense, isnt
it?
Yeah, and many people knew this stuff before
Newton wrote it all down.
However, Newton was able to explain the how
why, not just what happened. He was also able to
explain it using math terms, which nobody else
had done.
Newton was a genius, and for that
accomplishment, scientists named the unit of
force after him. Imagine if YOUR last name
replaced miles or ounces or quarts.
Pretty cool.
IT TAKES A FORCE TO CHANGE AN OBJECTS
MOTION Inertia!
13
12 Lets apply thatknowledge
Lets examine the forces acting on the ball.
If that was the only force acting on the ball,
then Newton would say that the ball MUST
MOVE DOWN!
14
13 But we know that it doesnt move down
So there must be a force counter-acting the
down force of the weight of the ballthat force
is the ground pushing back up!
(imagine if the ground wasnt strong enough
to push back with 7Nlike if it was tissue paper!)
15
14 So the forces are balanced?
Yep. And Newton would say that balanced
forces will result in no change of motion for the
object.
To get the ball rolling, youll need to apply a
force that is too strong to be balanced by
friction. Just kick the stupid thing!
16
15 So, Newton basically said
Unbalanced forces will change the motion of an
object. Thats the point of his 1st Law.
Studying balanced unbalanced forces is more
an 8th grade thing, so were a little ahead of
ourselves, but this will help make more sense of
things in a few days when we learn more about
inertia.
UNBALANCED FORCES CHANGE AN OBJECTS MOTION
17
16 Summary so far
A force is a push or a pull.
Force is measured by the unit Newtons (N).
Sir Isaac Newton used forces to explain how
why objects move or change motion. He explained
this in his famous 3 Laws.
(well study this 1st law in more detail and
explain the word inertia a little later)
18
17 WORK!!!
Wellnot that kind of work
In science, work is done when a force moves
an object a distance in the direction of the
force.
19
18 More Work
Work is measured in Joules, abbreviated J.
To calculate work, use this math formula W F x
d (work force multiplied by distance)
As long as the force is in Newtons and the
distance is in meters, the amount of work done is
measured in Joules.
15 N x 4 m 60 J
20
19 Example of Work
J.J. pulls with 140 N of force on a bulldozer.
How much work does he do?
W F x d W 140 N x 0 m (hes not gonna budge
it an inch!) W 0 J (hell get tired pulling
and pulling, but hes accomplished zero work,
scientifically)
21
20 Work Example 2
Maria picks up her 25 N chihuahua to give it a
hug. It travels 150 centimeters upward. How
much work did she do?
Slow down, Hoss!
W F x d
W 25 N x 150 cm
W 25 N x 1.5 m
Be careful of tricks when doing these work
calculations
W 37.5 J
22
21 Last example
Tony does 54,000J of work by firing an arrow
150m into the air. How much force does the bow
provide the arrow?
W F x d
54,000J F x 150m
How do we figure out F?
54,000J 150m F
360N F
Your math knowledge is gonna come in handy during
this unit!
23
22 So why is knowing about work important?
because, like most things in life, theres a
hard way and an easy way to do most anything.
In a week or two, well start studying how
simple machines are devices that take advantage
of making the same amount of work at least FEEL
easier.
24
23 In summary
  • A force is a push or pull, measured in Newtons
    (N)
  • Sir Isaac Newton explained force motion in his
  • 3 Laws of Motion
  • The 1st Law of Motion basically says that it
    takes
  • unbalanced forces to change the motion of
    objects
  • If a force moves an object in its direction a
  • distance, then work has been done.
  • W F x d (measured in Joules, J)

25
24 And that is
Da End!
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