©weston, 2009 force! hmmm… force! hmmm… force! hmmm…
TRANSCRIPT
©Weston, 2009
FORCE!Hmmm…
FORCE!Hmmm…
FORCE!Hmmm…
FORCE!Hmmm…
FORCE!Hmmm…
FORCE!Hmmm…
FORCE!Hmmm…
FORCE!Hmmm…
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 thatit’s being pushed forward.
What’s happening to this dogsled?
Yeah, it’s definitelybeing pulled along.
#2 So, let’s define Force
Notes – Force & Newton’s Laws
(write your name)
I. Force – a push or a pull.
So…anything you can think of that is a push or a pull…likethe air blowing from the air conditioner in the room to a leoparddragging away its kill is showing force at work.
#3 What are some examples of forces?
Here are some examples…think about how each isa push or pull:
•Gravity
•Weight
•Electro-magnetism
•Friction
#4 Write it
Notes – Force & Newton’s LawsI. Force – a push or a pull.
•examples: gravity, weight, electromagnetism, friction
#5 Force Amounts
Forces come in different amounts. You’d muchrather 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 Nto equal a pound of force.
#6 Measuring Force
The precise amounts of force exerted are usually measured with toolslike these:
Notes – Force & Newton’s LawsI. 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 toget it for him.
#8 Joe Tries the Force…
…clearly,the fridge doesnot move.
#9 Joe Puts some Elbow Grease Into it…he pulls!
…and since a force is both an amount and a direction, wecan use an arrow to symbolize it.
200N
…but the fridge doesn’tmove. Somebody explainwhy?
Right! Frictionbetween the fridgeand floor is the sameamount as Joe’s force.
We call this balancedforces.
200N
#10 Balanced Forces
Balanced forces exist when two or more forces combine to be inopposite directions but the same amount. The overall effect is thatthey cancel each other out.
A tug-of-war usually startsout featuring fairly balancedforces. Well, at least for a second or two.
50N 30N 20N
#11 Write it!
Notes – Force & Newton’s LawsI. Force – a push or a pull.
•examples: gravity, weight, electromagnetism, friction •measured in a unit called “newton” (N).
A. Balanced Forces – cancel each other outand do NOT change an object’s motion
#12 The Tug-of-war gives Joe an Idea…
Pull, boy, pull!
200N500N
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 canceleach other out. This will result in an acceleration of some sort (a change in motion such as speeding up, slowing down, or changingdirections).
25N 10N 20N
Yeah. Tug-of-wars aren’t reallyany fun until unbalanced forcesresult in victory and defeat.
#15 Write it down
Notes – Force & Newton’s LawsI. Force – a push or a pull.
•examples: gravity, weight, electromagnetism, friction
A. Balanced Forces – cancel each other outand do NOT change an object’s motion
•measured in a unit called “newton” (N).
B. Unbalanced Forces – don’t cancel, so theyresult 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 neverhappened, but seeing an apple fall and hit the groundvery well could have inspired greatness.
Sir Isaac Newton lived in Englandfrom 1642 to 1727. Let’s see why he’s a famousguy. He is credited with helping invent calculus,a type of math that made going to the moonpossible 300 years later. He described how gravity works in both words and mathematical terms. Hisbook, 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 aunit 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?
•Gravity—the force of attractionbetween the Earth and the ball.
G
•The ground’s strength. After all,it’s not like the ball is drilling a hole into the ground.
ground
•The wind is blowing lightly.
air
•Friction—the force thatopposes motion when objectstouch, fights against the air.
F
No wonder soccer balls justsit there, just like your desk ora book, or whatever. The forcesare all _____________!balanced
#20 1st Law, contd.
So, how do you get a soccer ball (or a book or a desk) to change itsmotion?
Kick it!
Right, Joe! Apply an unbalancedforce to it! (must.sound.like.Newton)
Gground
air
FThis totally powerful, unbalanced force will cause a change inmotion…from sitting still to rolling way down the field.
#21 Inertia
But replace the soccer ball with…oh, say…a lawnmower.
The lawnmower might movean inch. The soccer ballwent 50 meters. Why?
If you said “cuz the lawnmower is way heavier” then well, you’resorta right. Newton would say, though, that it’s because the lawn-mower has way more mass. And because it has more mass, it hasmore inertia—it resists being accelerated. This gets us to Newton’s 1st Law.
#22 Write it!
B. Unbalanced Forces – don’t cancel, so theyresult in acceleration (change in motion)
II. Newton’s Laws of MotionA. 1st Law:
An object at rest will stay at restor
An object in motion will stay in motionin a straight line at the same speed
•unless an unbalanced force changes its motion•Objects with more inertia (mass) resistchanges 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 movethe bottle downward. You suddenlystop the bottle in mid-air, and ketchupcomes 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 theketchup has inertia—it doesn’t want to stop because it’s now inmotion. So it keeps moving. Out the bottle. Onto your fries.
#24 Have you ever…
…seen this guy’s show?
You might remember inthe intro song, a woman’svoice saying, “Inertia is a property of matter.”
Well, that’s true and all, but that’s not the kind of explanation that willhelp make the idea of what inertia is any clearer to you if you don’talready get it. That’s what this PowerPoint is for.
•Inertia is NOT a force
#25 Here’s Joe
Joe, we’re going to test your strength a littlebit. That’ll help us see inertia in action, too.
#26
Bring it on!
I’m a
BEAST!…uhhh…ok, Joe. Whatever.
#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 workYeah, and wave it around a little…
Pretty easy, huh.
Yeah
#30 Joe’s 2nd 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 atrest; an object in motion will stay in motion…”????
Speaking of an object at rest…can
I sleep now?
#34 Think about moving an object…
…whether it’s a feather or a boulder.
Feather Boulder
•Objects resist any change in their motion
Easy to start moving Hard to start moving
Easy to stop moving Hard to stop moving
(objects at rest want tostay at rest)
(objects in motion want to stay in motion)
Easy to curve its path Hard to curve its path (objects in motion want to continue in astraight path)
Easy because of lessmass (less inertia)
Hard because of highmass (more inertia)
Has inertia, justnot a lot of it
Has LOTSof inertia
#35 Inertia is Everywhere!
Why you lean in a cargoing around a corner…
Why you get mashed intothe seat when you gas it!
Why you leaaaaanforward 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 themath:
F = m x a (Force equals mass times acceleration).
Don’t worry about trying to understand the math or start workingproblems in your head. This Law is just a natural extension of the1st 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, acceleratejust 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) resistchanges 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 waswhy it can launch, then how wouldit continue to travel upward whenthe flames no longer touched theground?How would it ever get back home?Here’s the real reason why:
ACTION
REACTION
For every action, there isan equal and oppositereaction.
#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 equaland 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 overallmeaning of each law without worrying about all the littledetails and possibilities that could make these a LOT worse!
#43 And FINALLY, that’s…