Download LAWS OF MOTION interview

LAWS OF MOTION interview
Objectives:




to role play three famous scientists
to discuss the contribution of each scientist to the Laws of Motion
to be aware of the changes in ideas about motion through the centuries
to learn Newton's 3 Laws of Motion
Materials - Class Set :






Brief Biographies of Aristotle, Galileo, and Newton
Aristotle Interview
Galileo Interview
Newton Interview
Funny Wizard Hat
Self Quiz- Can be taken online or photocopied
Procedure:
1. Hand out Interview Sheets
2. Have students sit in a circle and chose 2 volunteers for each interview.
3. The Interviewer is a Wizard and wears a funny hat
4. Briefly introduce each scientist to the class
5. Have students act out interview.
6. Discuss the main points that are addressed in the Summary
7. Open floor for questions
8. Proceed to next Interview
Analysis/Results/Conclusion:
Have students complete self quiz and write a brief summary of what they learned
____________________________________________________________________
Script
ARISTOTLE
All right, wasn't that time travel amazing! Well, we are going to try and find
Aristotle.Before we talk to him, let me warn you! We came here to visit him, not
because he was right, but because he was wrong! His ideas were believed to be true
from 500 BC to 1600 CE. That's about 2000 years of false knowledge. What Aristotle
taught, appeared to be correct because it seemed obvious, but not all things are
obvious.
" Wait, I see him now." There he is! Lets go talk to him. "Hello Aristotle!"
"Great Zeus! You seem to be a god that has descended from the heavens. That hat of
yours is enigmatic of your strength. I am at your mercy, oh Great One"
"Thanks, for the praise, but I'm no god, but for your purposes, I am a person who
wishes to know more about your theory about the motion of objects"
"Ahh yes, I'd love to share that with you. I believe all motion is linear on the planet
Earth: meaning everything moves in a straight line. Let me show you. If I throw this
rock, it will travel in a straight line, and also fall in a straight line….
The way Aristotle thought
projectiles moved
The way projectiles
"really" move
In addition, when I drop this feather and rock at the same time, the rock will fall to the
ground first. Why you ask? Well, that's because I believe that the Earth pulls on
objects according to their weight.This means that a large heavy object will fall to the
ground faster than a large light object."
The way Aristotle 'saw'
objects to fall on the Earth
As we know, or will
know in the next few sections, objects
actually fall like
this in a friction free environment (vacuum)
"Is that all Aristotle?"
"Of course not, there also exists a natural motion with each object. This is the motion
an object has when it is as rest and when it is moving in a straight line at uniform
speeds. This natural motion is also prevalent in the heavens - the great glass spheres
that rotate around the center of the universe - our planet Earth."
"Ummm yes?!? Well Aristotle, how do you account for motion that isn't at constant
speeds??"
"Well my under-educated friend, this is what I call violent motion. You see motion
also depends on an applied movement. Once this movement stops, the motion of the
object stops. For example, if I push this cart, the cart keeps moving until I stop
pushing. That's all I'm going to talk about today. Good day sir."
Well, I hope you see how Aristotle's view on motion seems to make sense.
Unfortunately, it isn't correct. But because his theories appeared to make sense, they
became popular and well accepted for a very long time. The key ideas that Aristotle
tried to teach were:
All motion on the Earth is linear .
All motion in the heavens (outer space) is curved .
The speed at which an object falls is directly related to the mass of an object .
Motion could be considered in two main factions: natural and violent.
Motion continues so long as there is only an applied motion to an object. Removing
the motion stops the object.
It would take a man named Galileo to start the wheels of change in this field of
knowledge called physics.
Click on the time machine to proceed to visit the next person on our voyage: Galileo
__________________________________________________________
GALILEO
Here we are, in jolly old Italy. The time is about 1600, and as I promised we are going
to meet the man with the name that makes us all laugh. "Galileo Galilee" Ah ha , there
he is. "Hello Mr. Galilee. Could I ask you a few questions, please?" .
"Sure sir, only just don't poke my eye with your *enchanted* hat."
"Okay. I wanted to know, what do you think about motion?"
"Well I have a lot to say but I'll try to make it quick. First, I think, unlike Aristotle,
that motion to the Earth does not depend on the weight of an object. Rather, I believe
all objects fall to the ground at the same speed. Let me show you an experiment I did
on top of the leaning Tower of Pisa."
This is what Galileo would have seen at Pisa - two balls with unequal masses both fall in the
same time. (There was little wind on the day of Galileo's experiment, so friction was minimal)
"So you see, the speed at which an object falls at has nothing to do with the mass of
the object. All objects that are released from the same starting point reach the ground
in the same time. My theory unlike Aristotle unifies the concept of what I call force
and mass."
"WOW! That's an amazing observation Galileo, but if you're right why then does a
feather not fall in the same time as say a rock??"
"Well my friend, you see I have asked myself the same question, and I came up with
an answer that I think you would find particularly interesting. I think that all objects
have an opposing force to motion - a force that retards the motion. This is the force
that slows down the feather - the flat and thin surface of the feather is pushed up by
the retarding forces in the air. The rock, because it is more sleek, is less prone to these
effects, and hence falls to the ground in less time. My theory though is that if the
feather and the rock were placed in a vacuum (absence of all matter) they would fall
in the same time - it is the air that slows down the feather not the Earth."
"Very true Galileo, now I have also heard that you have had some theories about
motion in general - why objects don't stop immediately as soon as you remove an
applied force - as Aristotle thought."
"Quite true, you see I played a mind game with myself a while ago - I saw that when
you roll a ball down a ramp such that it rises up the path in its path, that the ball
essentially rolls up the plane to its original height. But in time, the ball slows down,
not reaching the original height it had to begin with I wondered, and asked myself
what slows down the ball - well, like the feather, I figured there must be some form of
resistance on the ball slowing it down, only it was not the air this time, but the surface
of the ball and the plane. I called this force friction. It explains why when you push a
cart the cart slows down to a stop when you stop pushing - the friction opposes the
motion of the cart, hence slowing it down. Back to the plane, if the angle of the
second ramp were to decrease, the ball would 'try' reach a height original to the
release height. Now this model assumes there is no opposing force - friction. I thought
about this model some more and realized that if the angle of the second ramp was
made to approach 0, the ball would keep rolling in a straight line in constant speed.
The above depicts the thought experiment Galileo "thought of" (Now doesn't that make sence!)
This 'observation' gave me a revelation and prompted me to hypothesize that all
objects want to move in a straight line at constant speeds. What prevents them from
doing so is an external unbalanced force, like friction. This deduction prompted me to
think of another observation of objects - since they all want to stay in motion in a
straight line in constant speed, they resist changes in motion by trying to stay in
motion - a property I call Inertia. If that sounds complicated, let me give you an
example. When you're pushing a cart loaded with packages, while you are moving
with a constant speed, the package remains at rest on the cart. However, if you
suddenly brake or stop the cart, the package on the cart slide to the front of the cart.
Why? Because the package had inertia to stay moving at the original speed of the cart.
It wanted to maintain that balance. Now you may ask what stops the package from
continuing its intent, well, as I mentioned, friction slows the package as it moves, and
if the package hits anything on its way, its motion is retarded by it as well."
Note how the package slows down, and does not move at a constant (uniform) speed. The
package is affected by the retarding force of friction
"Very good points Mr. Galilee, thank you for your time, and I hope things go well for
you."
"Well thank you Mr. Wizard type of person sir, I hope you get a better hat. Good
day!"
Well to give you a summary of our conversation with Galileo, he essentially stated
that all objects when released from the same point, reach the ground in the same time,
providing a minimization of air resistance. In fact, the hypothesis Galileo had was
right, as when the same experiment with the rock and the feather was performed in a
vacuum, some decades later, both fell to the ground in the same time, as there was no
air resistance on the feather or the rock. In case you don't know a vacuum is when
there is no matter in a volume. In case this concept isn't very clear, don't worry, as our
conversation with Newton will help to clear this up. In addition to this, Galileo spoke
of his famous thought experiment, that led to the conclusion that all objects want to
move in a straight line at a constant speed. This property of an object wanting to
maintain this property was called inertia. The final point Galileo spoke of in our
conversation was that all objects have an opposing force called friction that slows the
object down.
We will talk to Galileo again, but for our next lesson in Motion, we will hear from the
man who was thought as the father of physics - Sir Isaac Newton. So to voyage to his
neck of the woods, click on the time machine.
According to Galileo, the motion of a falling object is independent of mass.
Meaning two objects of unequal masses will fall to the ground when dropped from a
set height in equal times
The reason why objects did not always fall in the samwe time was because of a
retarding force called friction.
NEWTON
Our voyage in time now takes us to the land where tea, cricket and the Spice Girls are
popular. That's correct, we're in England. Here we will meet perhaps the most
revolutionary scientist in history, Sir Isaac Newton. In fact, here he is right now!
"Hello Mr. Newton sir, can I ask you a few questions please??"
"Ahh! What hideous kind of hat is that??"
"Um yah, I've been getting comments about it. Now, about those questions, would you
please explain to me and my Internet friend here, your laws of motion you discussed
in your book Principia?"
"Of course. Well my first law really isn't my law at all. I borrowed it from Galileo and
got the credit, but it's okay since Galileo 'borrowed' ideas as well. Anyway, my first
law is that An object will maintain its state of rest or constant speed in a straight line
unless acted upon by an external unbalanced force. In other words, bodies want to
stay in motion in a straight line at a constant speed, or at rest. This was referred to by
Galileo as inertia. Thus, objects try to resist changes in motion when acted upon by an
external unbalanced force. Thus, my first law attempts to set up or describe motion's
tendencies. My second law relates this property to mathematics and explains why
objects move. My second law states: When an external unbalanced force is applied to
an object at rest or in constant speed in a straight line, the object accelerates in the
direction of the unbalanced force. Furthermore, the acceleration of the object is
directly proportional to the net forces acting on the object, and inversely proportional
to the mass of the object being accelerated"
"Wow that's a mouthful Newton, perhaps you could simplify that a bit for me."
"No problem. Essentially when you apply forces (a push or a pull), the sum of all the
forces is the direction in which the object accelerates. If the object is really heavy, it
won't accelerate as fast; whereas if it's light, and the same force is applied, the object
will have a greater acceleration. Mathematically this relationship is as follows:
F=ma
(F is the sum of all the forces acting upon the object, m is the mass of the object, and a
is the acceleration of the object.)
So you see, this relationship allows us to predict which way and with what
acceleration an object will move when a certain specified net force is applied to an
object."
"That is totally gnarly dude! Such a simple concept, yet it can be applied for many
practical applications! Tell me more"
"Of course, but only if you refrain from using such awkward tenses of English like
gnarly or dude. Anyway, my third law is perhaps the most recognized, but the most
misunderstood. This law states that: When an object exerts a force on a second object,
the second object will exert a force of equal magnitude, and opposite direction on the
first object" This law is most commonly stated as 'for every action there exists an
equal and opposite reaction.' The flaw in this version is that it doesn't say that the
forces exerted are on different bodies. Thus, the forces do not simply cancel out as
some may expect, rather they are transferred to the other object. My favorite example
of this law is exhibited by cannon fire. When you fire the cannon, the cannon ball is
pushed forward by an explosion in the cannon.
My law kicks in when the explosion happens. As the bullet is pushed forward by the
gun, the bullet pushes back on the gun. This is seen by the jerk in the rifle when it is
fired. So, the force the gun pushes on the bullet is equal to the force the bullet pushes
back on the gun."
"Fascinating Newton! But I don't understand why when the gun is fired, the gun and
man shooting don't get pushed back as fast as the bullet?"
"Good question. You see if you look back to my second law, force is inversely related
to mass. Because the mass of the bullet is very small compared to the mass of the gun
and man, they don't accelerate backwards as quickly. However, they do get the same
force returned to them. The reason why this force doesn't kill the man is because most
of the 'pain' is absorbed by the barrel of the rifle (gun)."
"Very neat, but I have one more question. Why is it that the man firing the gun doesn't
slide backwards when he fires the gun?"
"An excellent question. You see when the man is pushed back by the bullet, he has a
retarding force exerted upon him. Galileo first noted this force, which I call friction.
This frictional force slows the shooter down very quickly, if he is exerting a lot of
pressure on the ground, or if the ground is very rough. But you see, if the shooter were
to fire his bullet standing on a friction-less surface, then he would be pushed back
such that he would keep moving for ever."
"A very interesting discussion. Thank you for your time Newton."
"A pleasure, and perhaps next time we meet you could change your hat."
"Ha Ha"
There are three main laws of motion Newton described. Firstly:
1.)An object will maintain its state of rest or constant speed in a straight line unless
acted upon by an external unbalanced force
2.) When an external unbalanced force is applied to an object at rest or in constant
speed in a straight line, the object accelerates in the direction of the unbalanced
force. Furthermore, the acceleration of the object is directly proportional to the net
forces acting on the object, and inversely proportional to the mass of the object being
accelerated (F=ma) "
3.) When an object exerts a force on a second object, the second object will exert a
force of equal magnitude, and opposite direction on the first object
In addition to Newton's laws, he discussed the concept of friction. This is the same
force described by Galileo as the retarding force. Although it was not exactly stated
by Newton, the force of friction is related to the amount of pressure you apply at a
point. Friction is not related to area. In general terms, friction is when two dissimilar
surfaces interact with each other creating an opposing force. But, friction also occurs
with objects that are very similar such as glass. If you put two sheets of glass on top of
each other and try to move one of them, you will see that it is very difficult. This is as
a result of molecular bonding that forms quickly when the two pieces of glass are put
on top of each other. Thus the two pieces essentially bond to be become one piece.
Since it is hard to break molecular bonds, the person who pushes the glass experiences
difficulty - a resistance force - friction. Thus, friction is also noted to exist when you
exert a force on an object that rests on a similar object.
______________________________________________________________
BRIEF BIO OF THE THREE SCIENTISTS
Did you Know? – GALILEO GALILEIDid you Know? Galileo Galilee was born in 1564 and died in 1642. He is most famous for his
many thought experiments in motion. As well, he made astronomical discoveries,
such as the moons of Jupiter.But, Galileo was perhaps best known for his battle with
the Church. He agreed with the philosophy that the planets revolved around the sun.
This heliocentric model was first popularized by Nicholas Copernicus of Poland.
Galileo was a very popular man in Italy and had contacts in high places. Despite this,
he wrote the various publications of his ideas and concepts in Italian as opposed to
Latin. As a result, all the common folk could understand what Galileo was saying.
Inspite of Galileo's great contributions to science, the church tried to stop his work. In
fact, they forced him to retract his theories and state that the Earth was the center of
the universe. Galileo's publications were not recognized by the church as late as 1979
- more that 300 years after his death.
If you want more information on Galileo or other scientists, visit one of the following
web pages: A page describing the differences between Aristotle and Galileo
: http://csep10.phys.utk.edu/astr161/lect/history/aristotle_dynamics.html
A list of many scientist's
biographies: http://hermes.astro.washington.edu/scied/physics/physbio.html
NEWTON
Did You Know? Newton Isaac Newton was born in the year of 1642, and died in 1727. He was most
famous for his three laws of motion, but was also known for other major discoveries
in math and science. He compiled most of his work into a masterpiece of science
called the Principia. Newton was known to be arrogant, so his book was written
almost exclusively for the elite and rich. Some people claim that only 50 people in
history have been able to understand his style of writing. Despite his arrogance, he
truly was a father in the field of science. At the age of 18, he had devised a new
system of mathematics called Calculus, and developed three laws which resulted in a
new way of understanding motion.. All of this happened at his farm while the Black
Plague swept across England. In the Principia, Newton claimed to have "discovered"
gravity when an apple fell on his head. But, many now believe that this was just a
story told by Newton, and that in real life, he discovered gravity through thinking not seeing.
If you want more information on Newton or other scientists, visit one of the following
web pages: A very comprehensive and detailed account of Newton and his works:
http://csep10.phys.utk.edu/astr161/lect/history/newton.html
A list of many scientist's
biographies: http://hermes.astro.washington.edu/scied/physics/physbio.html
A list of many scientist's
biographies: http://hermes.astro.washington.edu/scied/physics/physbio.html
http://www.middleschoolscience.com/motioninterview.htm
http://library.thinkquest.org/11924/aristotleinfo.html
http://library.thinkquest.org/11924/galileo.html
http://library.thinkquest.org/11924/newtoninfo.html
http://library.thinkquest.org/11924/aristotle.html
http://library.thinkquest.org/11924/newton.html
http://library.thinkquest.org/11924/gather/mcq1.html