Download FORCE!

©Weston, 2009
Hmmm…
FORCE!
Hmmm…
FORCE!
Hmmm…
FORCE!
Hmmm…
FORCE!
Hmmm…
FORCE!
Hmmm…
FORCE!
Hmmm…
FORCE!
Hmmm…
FORCE!
Um, dream on, Joe.
This is more like it.
Yep. That’s force.
#1 FORCE
What’s happening to this bobsled?
You’d probably say that
it’s being pushed forward.
What’s happening to
this dogsled?
Yeah, it’s definitely
being pulled along.
#2 So, let’s define Force
So…anything you can think of that is a push or a pull…like
the air blowing from the air conditioner in the room to a leopard
dragging away its kill is showing force at work.
(write your name)
Notes – Force & Newton’s Laws
I. Force – a push or a pull.
#3 What are some examples of
forces?
Here are some examples…think about how each is
a push or pull:
•Gravity
•Weight
•Electromagnetism
•Friction
#4 Write it
Notes – Force & Newton’s Laws
I. Force – a push or a pull.
•examples: gravity, weight, electromagnetism,
friction
#5 Force Amounts
Forces come in different amounts. You’d 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
FYI…a newton isn’t very much. It takes about 4.5 N
to equal a pound of force.
#6 Measuring Force
The precise amounts of force exerted are usually measured with tools
like these:
Notes – Force & Newton’s Laws
I. Force – a push or a pull.
•examples: gravity, weight, electromagnetism,
friction
•measured in a unit called “newton” (N).
#7 Combined Forces
Joe’s dog, Rex, lost his squeaky toy under the fridge. Joe wants to
get it for him.
#8 Joe Tries the Force…
…clearly,
the fridge does
not move.
#9 Joe Puts some Elbow Grease
Into it…he pulls!
…and since a force is both an amount and a direction, we
can use an arrow to symbolize it.
…but the fridge doesn’t
move. Somebody explain
why?
200N
200N
Right! Friction
between the fridge
and floor is the same
amount as Joe’s force.
We call this balanced
forces.
#10 Balanced Forces
Balanced forces exist when two or more forces combine to be in
opposite directions but the same amount. The overall effect is that
they cancel each other out.
50N
30N 20N
A tug-of-war usually starts
out featuring fairly balanced
forces. Well, at least for a
second or two.
#11 Write it!
Notes – Force & Newton’s Laws
I. Force – a push or a pull.
•examples: gravity, weight, electromagnetism,
friction
•measured in a unit called “newton” (N).
A. Balanced Forces – cancel each other out
and do NOT change an object’s motion
#12 The Tug-of-war gives Joe
an Idea…
Pull, boy,
pull!
500N
200N
200N
#13 With 700 total newtons
pulling against 200 newtons…
That’s the beauty of unbalanced forces!
#14 Unbalanced Forces
Unbalanced forces exist when forces on an object do not cancel
each other out. This will result in an acceleration of some sort
(a change in motion such as speeding up, slowing down, or changing
directions).
25N
10N
20N
Yeah. Tug-of-wars aren’t really
any fun until unbalanced forces
result in victory and defeat.
#15 Write it down
Notes – Force & Newton’s Laws
I. Force – a push or a pull.
•examples: gravity, weight, electromagnetism,
friction
•measured in a unit called “newton” (N).
A. Balanced Forces – cancel each other out
and do NOT change an object’s motion
B. Unbalanced Forces – don’t cancel, so they
result in acceleration (change in motion)
Man. That’s a lot of information about forces.
Just remember that a force is a push or a pull,
and that when unbalanced forces act on objects,
they cause a change in motion.
#16 An Old English Dude
You’re probably familiar with this legendary tale:
An apple falling on this guy’s head likely never
happened, but seeing an apple fall and hit the ground
very well could have inspired greatness.
Sir Isaac Newton lived in England
from 1642 to 1727. Let’s see why he’s a famous
guy. He is credited with helping invent calculus,
a type of math that made going to the moon
possible 300 years later. He described how gravity
works in both words and mathematical terms. His
book, Principia, is considered one of the most
important books ever written. (continue)
#18 Newton!
Newton was so recognized for his greatness and brilliance, that
scientists agreed that the unit of force should be named after him,
which you learned several slides ago. Wow. How neat to have a
unit of measurement named for you! What if “gallons” or “tons” or
“inches” got changed to YOUR last name. Cool!
I’m gonna
play the
lottery and
win a million
Joes.
Even Newton had his influences.
Here’s a quote of his:
“If I have seen further it is by
standing on the shoulders of
giants.” Newton was talking
about his own heroes like
Aristotle, Copernicus, & Galileo.
#19 Newton’s 1st Law of
Motion
Here’s a soccer ball. What forces are acting on it?
air
No wonder soccer balls just
sit there, just like your desk or
G
ground
a book, or whatever. The forces
balanced
are all _____________!
F
•Gravity—the force of attraction
between the Earth and the ball.
•The ground’s strength. After all,
it’s not like the ball is drilling a
hole into the ground.
•The wind is blowing lightly.
•Friction—the force that
opposes motion when objects
touch, fights against the air.
#20
st
1
Law, contd.
So, how do you get a soccer ball (or a book or a desk) to change its
motion?
Right, Joe! Apply an unbalanced
force to it! (must.sound.like.Newton)
Kick it!
air
G
ground
F
This totally powerful, unbalanced force will cause a change in
motion…from sitting still to rolling way down the field.
#21 Inertia
But replace the soccer ball with…oh, say…a lawnmower.
The lawnmower might move
an inch. The soccer ball
went 50 meters. Why?
If you said “cuz the lawnmower is way heavier” then well, you’re
sorta right. Newton would say, though, that it’s because the lawnmower has way more mass. And because it has more mass, it has
more inertia—it resists being accelerated. This gets us to Newton’s
1st Law.
#22 Write it!
B. Unbalanced Forces – don’t cancel, so they
result in acceleration (change in motion)
II. Newton’s Laws of Motion
A. 1st Law:
An object at rest will stay at rest
or
An object in motion will stay in motion
in a straight line at the same speed
•unless an unbalanced force changes
its motion
•Objects with more inertia (mass) resist
changes in motion better
#23 So, what’s this mean?
Ever done this to get the stubborn last bits of ketchup out of a bottle?
You turn it over, and quickly move
the bottle downward. You suddenly
stop the bottle in mid-air, and ketchup
comes out where you need it.
You put two objects in motion (the bottle and the ketchup inside).
You stop one object with your unbalanced muscle force, but the
ketchup has inertia—it doesn’t want to stop because it’s now in
motion. So it keeps moving. Out the bottle. Onto your fries.
#24 Have you ever…
…seen this guy’s show?
You might remember in
the intro song, a woman’s
voice saying, “Inertia is a
property of matter.”
•Inertia is NOT a force
Well, that’s true and all, but that’s not the kind of explanation that will
help make the idea of what inertia is any clearer to you if you don’t
already get it. That’s what this PowerPoint is for.
#25 Here’s Joe
Joe, we’re going to test your strength a little
bit. That’ll help us see inertia in action, too.
#26
Bring it on!
I’m a
…uhhh…ok, Joe. Whatever.
BEAST!
#27 Joe, Here’s your 1st
Challenge
Ready!
Joe, pick up this…
…
…
…
Feather!
#28
Um,
seriously?
Joe, just do it.
#29 Joe, “The Beast,” at work
Yeah, and wave it around a little…
Pretty easy, huh.
Yeah
#30 Joe’s
nd
2
challenge!
Yeah, now what? Eat a whole…
GRAPE? Tie my…SHOES??
Ooooooooooooooh!
No, Joe…wave around this boulder!
#31
#32 Joe, “The Beast!”
Dude, this
is hard!
Pretty difficult, huh, Joe?
•All objects have inertia
•The more mass, the more inertia
#33 So Inertia Is…
•Inertia is a word used to say: “objects obey Newton’s 1st Law.”
Remember that one? The one that says “an object at rest will stay at
rest; an object in motion will stay in motion…”????
Speaking of an
object at rest…can
I sleep now?
#34 Think about moving an
Has inertia, just
object…
not a lot of it
…whether it’s a feather or a boulder.
•Objects resist any change in their motion
Feather
Easy to start moving
Easy to stop moving
Easy to curve its path
Easy because of less
mass (less inertia)
Has LOTS
of inertia
Boulder
Hard to start moving
(objectsinatmotion
rest want
(objects
wantto
Hard to stop moving tostay
stayatinrest)
motion)
(objects in motion
Hard to curve its path
want to continue in a
straight path)
Hard because of high
mass (more inertia)
#35 Inertia is Everywhere!
Why you lean in a car Why you get mashed into Why you leaaaaan
going around a corner… the seat when you gas it! forward when braking
Inertia is all around us!
#36 Newton’s 2nd Law of
Motion
This one involves a lot of math and word descriptions. Here’s the
math:
F=mxa
(Force equals mass times acceleration).
Don’t worry about trying to understand the math or start working
problems in your head. This Law is just a natural extension of the
1st Law. Here’s what it’s really saying:
“It takes a certain amount of force to cause a certain amount of
acceleration to an object of a certain size.” Remember, accelerate
just means a change in motion.
#37 Footballs
Ever seen a bored 6th grader flick paper footballs?
Well, that same amount of force applied to something with a lot
more mass won’t accelerate it nearly as much.
#38 Write it!
•Objects with more inertia (mass) resist
changes in motion better
B. 2nd Law:
Force = mass x acceleration
(A force will accelerate a mass a
certain amount)
#39 And Finally…Newton’s 3rd
Law!
Why does this space shuttle lift off the ground when its rockets fire?
…it’s not because the flames “push off” against the ground.
#40 It’s the same reason…
…why a balloon that you release goes flying all over the room.
Let’s see…
#41 Blast Off!
The space shuttle doesn’t “push”
against the Earth. If that really was
why it can launch, then how would
it continue to travel upward when
the flames no longer touched the
ground?
How would it ever get back home?
Here’s the real reason why:
For every action, there is
an equal and opposite
reaction.
R
E
A
C
T
I
O
N
A
C
T
I
O
N
#42 Newton’s 3rd Law…Write
it.
B. 2nd Law:
Force = mass x acceleration
(A force will accelerate a mass a
certain amount)
C. 3rd Law:
For every action, there is an equal
and opposite reaction.
Newton’s Laws aren’t always easy to understand,
especially the first time you hear them.
Fortunately, we’re just trying to get the overall
meaning of each law without worrying about all the little
details and possibilities that could make these a LOT worse!
#43 And FINALLY, that’s…