Download Physics Project - Michigan State University

Physics Project
Newton’s First Law of Motion
Submitted by: Shannon Carpenter
Michigan State University Teacher Education Student
Modified from Center of Excellence for Science and Mathematics Education at the University of
Tennessee at Martin
Date: November 16,2000
Grade Level: Appropriate for any general physics class in high school.
(Grades 11 and 12)
Requirement: Students should have completed some physics background before doing these demos.
Overview: These demos have been placed together into order to help students see the concept of
Newton’s Third Law. Students must use some of their prior knowledge of the subject before seeing
each demo. Included below: a short 10-minute lecture reviewing the concept of Newton’s Third Law
and four demonstrations which should be done within a one-hour class period. Each demonstration
should last around 2 or 3 minutes with about a 5 to 10-minute class discussion following each demo.
Student Objectives:
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Demonstrate ability of discussion and reasoning.
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Analyze demonstrations showing the concept of Newton’s First Law of Motion.
Teacher Objectives:
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Test student’s familiarity and knowledge of previous learned physics information/concepts.
(Examples: Forces on an object, gravity and friction.)
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Assess student’s understanding of Newton’s First Law of Motion.
10-minute lecture should discuss the following points of information:
Newton's first law of motion is often stated as: An object at rest tends to stay at rest and
an object in motion tends to stay in motion with the same speed and in the same
direction unless acted upon by an unbalanced force.
Unbalanced forces cause accelerations. Example: A Book sliding from left to right
across a tabletop.
There are two parts to this statement - one that predicts the behavior of stationary
objects and the other which predicts the behavior of moving objects.
The property of any object keeping its motion unless disturbed by others is called
inertia. Newton’s first law is also termed as the law of inertia.
The law is valid in an inertial frame, which does not accelerate with respect to the rest
of the Universe.
Newton’s thought was: if an object moves on a level floor, it stops because of friction.
If the floor is smooth, the object goes straight further. In the case of no friction, it will
move unchanged forever.
Demonstration #1:
Sugar Cubes and Hoop
Purpose:
Demonstrates "objects at rest tend to stay at rest".
Materials:
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Stack of Sugar Cubes
Large 12-inch Embroidery Hoop
Large Glass Narrow-Mouth Bottle
Procedure:
1. Very carefully balance the embroidery hook vertically on the mouth of the bottle. Stack one
sugar cube on top of the hoop. With practice a stack of sugar cubes can be used in place of the
single cube.
2. Face the hoop toward you so that you can see the full circle.
3. Swing your arm across your body horizontally, quickly grabbing the far inside edge of the hoop
while your arm is moving, and flicking your wrist to move the hoop from beneath the sugar
cubes.
4. The sugar cubes should drop into the bottle.
5. Next, try this again but this time grab the hoop on its near side.
Class Discussion Questions (with answers in italics):
1. Is inertia involved?
Yes
2. What kept the sugar cubes from scattering?
The hoop moves while the sugar cubes do not, other than to fall into the bottle. As long as the
sugar cubes rested on the hoop there were equal forces pushing up and pushing down on them and
they didn’t move. When, by snatching the hoop away, the upward force exerted by the hoop on the
sugar cubes was taken away the sugar cubes experienced an unbalanced force and started to move.
When they started moving they continued to move until another force, the bottle of the bottle, acted
on them and brought them to a halt.
3. What happened when I grabbed the hoop from its near side?
If you grab the near side of the hoop first, you momentarily stretch the hoop vertically, so that the
coins are tossed into the air - they may or may not land in the flask.
4. What part of Newton’s First Law of Motion does this demonstration illustrate?
"Objects at rest tend to stay at rest".
Demonstration #2:
Penny and Index Card
Purpose:
Demonstrates "objects at rest tend to stay at rest".
Materials:
•
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3 x 5 Index Card
One Penny
Procedure:
1. Cut the index card in half and place the penny in the center of the card and balance the card and
penny on your left index finger.
2. With your right middle finger flick the card off of your index finger. This should be done so
that the card moves in a horizontal plane and so the penny is able stay on the fingertip.
3. If the removal of the card is not done quickly both the card and the penny will move.
Class Discussion Questions (with answers in italics):
1. Have the students predict what will happen when you flick the card based on the previous
experiment.
2. Why doesn’t the penny fall on the ground with the index card?
The inertia of the penny accounts for it remaining where it started while the card
motion.
3. What part of Newton’s First Law of Motion does this demonstration illustrate?
"Objects at rest tend to stay at rest".
is set in
Demonstration #3
Inertia in an Automobile
Purpose:
For students discover the importance of wearing a seatbelt.
Demonstrates that a person in motion tends to stay in motion with the same speed and in the
same direction.
Materials:
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2 meter piece of string
1 dynamics cart
One 200-g hook mass
One rubber band
1 small doll (to fit the dynamics cart)
1 pulley
1 block of wood
Procedure:
1. Attach one end of the string to the dynamics cart and the other end to the 200-g mass.
2. Attach the pulley to the end of the desk and hang the mass over the pulley so that the mass is on
the floor and the cart is on the desk.
3. Place the block of wood on the table in front of the pulley (between the pulley and the cart).
4. Then place the doll on the cart.
5. Next, pull the cart back and release it so that it accelerates toward the edge of the desk.
6. Repeat this procedure, but this time, attach the doll to the cart with the rubber band or tape
which acts as the seat belt.
Class Discussion Questions (with answers in italics):
1. Why does the doll fly out of the cart when the cart hits the block of wood?
The force of the desk on the wheels provides the unbalanced force to change the car's state of
motion, yet there is no unbalanced force to change the doll’s own state of motion. Thus, the doll
continues to stay in motion, flying in a forward motion.
2. What part of Newton’s First Law describes this?
A person in motion tends to stay in motion with the same speed and in the same direction.
3. What is happening when the seat belt is applied to the doll?
The seat belt provides the unbalanced force, which brings you from a state of motion to a state of
rest.
4. What would be different if this collision had happened in zero-g (in a vacuum)?
If this collision had happened in zero-g, in a vacuum, the dummy would theoretically keep on
hurtling away from the car at the same speed the car was traveling.
Demonstration #4
Concept Extension
Purpose:
Illustrates multiple concepts surrounding Newton’s First Law.
Materials:
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Four pieces of thread about 3 meters long
2 Identical paperback books
Procedure:
1. Suspend from the ceiling or other horizontal support two pieces of thread that are 3 meters
long.
2. Wrap the first piece of thread around a paperback book allowing it to hang down.
3. Wrap the second piece of thread around an identical paperback book so that it hangs down an
identical distance from the ceiling.
4. Tie another piece of thread around the first book so that it hangs about one meter below the
bottom of the book. Both strings tied to the book should be in the same vertical line.
5. Repeat step #4 on the second book so that there are two identical setups.
Class Discussion Questions (with answers in italics):
1. What will happen when you pull on the bottom thread attached to the first book?
(If the students say the thread will snap above the book, jerk rapidly and the thread below the
book will snap. If the students say that the thread below the book will snap, pull slowly on the
thread and the thread above the book will snap.)
By pulling the thread slowly, we are not only putting a strain in the thread, but in the thread above
the book, the book’s weight adds to this pull. Thus compared to the strain below the book, this is
much larger and the thread snaps wherever the strain is the highest.
When a sharp jerk is exerted on the thread, the inertial of the book keeps the strain below the book.
Although there is some strain in the thread above the book, compared to that below the book, the
strain in the latter is still higher, and the thread snaps below the book.
Overall Assessment:
One type of assessment that you may want to do following the demonstrations could be a “journal”
type activity for the students to do. This would be a set of analysis questions based around Newton’s
First Law of Motion the students could do either individually or in a small group. This homework
activity should be due the next day following your demo presentations.
Here is one such example of this:
These questions were taken from http://www.lerc.nasa.gov/WWW/K-12/BGA/Sheri/ newton %27s_
first_law_wks.htm:
1. An F18 Hornet aircraft sits motionless on a runway because of inertia. If that plane starts to
move down the runway, it means that there must be a force acting on it. Of the four main forces
that act on aircraft, which one is most likely to cause the forward motion down the runway?
2. Which of the four forces causes the airplane to become airborne?
3. Once the F18 Hornet is airborne, which force is equal to the force of thrust?
4. As the F18 Hornet travels at constant velocity, it burns fuel, which decreases its weight. In
response to this decrease, which of the four forces is also likely to decrease?
Consider the situations below to determine whether or not there is an external force acting on the
airplane. Remember that according to Newton's First Law, a plane will resist a change in its state of
rest or motion unless it is acted on by a force. Write the word force next to the situations where an
external force acts.
1.
2.
3.
4.
5.
6.
The F18 is flying at 200 mph at an elevation of 30,000 ft.
The F18 turns northeast at 200 mph and an elevation of 30,000 ft.
The F18 increases its speed to 220 mph at the same elevation.
The F18 continues flying at 220 mph at 30,000 ft.
The F18 drops to an elevation of 28,000 ft.
The F18 heads due east maintaining its speed and elevation.
Strengths of Exercise: These exercises are a good experience for students to see that science can be
fun and interesting, if they “see” physics as being something that is all around them and very
applicable such as Newton’s First Law is. The exercise is also good because it depends somewhat on
the prior knowledge of certain basic physics concepts and laws. These demonstrations also allows for
student-student interaction/discussion when a class discussion is done after each demonstration.
What to Look Out For: As in all class discussion type situations, it is necessary to make sure that all
of the students are included in the discussion and that one person does do all of the participating. Also,
you make sure to give some time (more than 3 seconds) between asking questions and receiving
answers so students have some time to think about the answer. One good way of doing this is to have
the students write done their answers individually before any of the students even answer them.