Download The Web of Newton`s Laws

Phys/Chem- Phys Unit 2 Newton’s Laws
Students will: Define Forces: Normal, Frictional, and Weight.
Describe motion of object if all forces are balanced. Describe acceleration if Force is increased or
decreased by integral multiples. Describe acceleration if mass is increased or decreased by integral
multiples.
Category
Homework/
Activities
(30%)
Title
Date
Due
Possible
Points
Read pp.88-97: PP(practice problems) #1-3,5-7,10 p. 92
10
Practice Quiz
10
Video Quiz
10
Web of Newton’s Laws Lab
20
FBD Lab
10
Evaluation Quiz
20
(60%)
Newtons’ Laws
1. INERTIA
2. F=ma
3. ACTION/REACTION
Points
Earned
The Web of Newton’s Laws
Name:
Block:
Go to: Physicsclassroom.com
>Physics Tutorial
>Newton’s Laws
>First Law: Look at the animations that illustrate the laws.
>Second Law, Third Law
Read the descriptions, then go back to the animations. Then answer the questions.
1a). State Newton’s First Law:
Sum it up in one word:
b) Draw a picture of an example from the animations.
(http://physicsclassroom.com/Class/newtlaws/U2L1a.html
c) Explain the example in words.
d) Draw a picture of a new example of your own.
2a). State Newton’s Second Law:
Sum it up in a phrase or an equation.
b) Draw a picture of an example from the animations.
(http://physicsclassroom.com/Class/newtlaws/U2L3e.html)
c) Explain the example in words.
d) Draw a picture of a new example of your own.
3a). State Newton’s Third Law:
Sum it up in a phrase.
b) Draw a picture of a new example of your own.
c) Explain the example in words.
DRAWING FREE BODY DIAGRAMS
Name:
Block
In this lab, you will use the physicsclassroom website which has an excellent 1 page
tutorial on drawing free body diagrams. Take notes in the space below. After you have
browsed and noted the instructions, try the questions below.
Web Page: http://physicsclassroom.com/Class/newtlaws/U2L2c.html
Notes Here:
1. A book is at rest on a table top. Diagram the forces acting on the book.
2. A girl is suspended motionless from a bar which hangs from the ceiling by two
ropes. Diagram the forces acting on the girl.
3. An egg is free-falling from a nest in a tree. Neglect air resistance. Diagram the
forces acting on the egg as it falls.
4. A flying squirrel is gliding (no wing flaps) from a tree to the ground at constant
velocity. Consider air resistance. Diagram the forces acting on the squirrel.
5. A rightward force is applied to a book in order to move it across a desk with a
rightward acceleration. Consider frictional forces. Neglect air resistance. Diagram the
forces acting on the book.
6. A rightward force is applied to a book in order to move it across a desk at
constant velocity. Consider frictional forces. Neglect air resistance. Diagram the
forces acting on the book.
7. A college student rests a backpack upon his shoulder. The pack is suspended
motionless by one strap from one shoulder. Diagram the vertical forces acting on the
backpack.
8. A skydiver is descending with a constant velocity. Consider air resistance. Diagram
the forces acting upon the skydiver.
9. A force is applied to the right to drag a sled across loosely-packed snow with a
rightward acceleration. Diagram the forces acting upon the sled.
10. A football is moving upwards towards its peak after having been booted by the
punter. Neglect air resistance. Diagram the forces acting upon the football as it rises
upward towards its peak.
11. A car is coasting to the right and slowing down. Diagram the forces acting upon
the car.
Friction Lab
Name: __________________Partners: _________________
Purpose: To investigate the effect of certain surface conditions on the force of friction
Materials:
wood block
various weights
string
different sandpaper types
spring scale
We are constantly aware of the frictional force that opposes the motion of one surface
over another. A sheet of ice on a sidewalk reduces friction and makes it difficult to walk
safely. The lack of friction is not only an inconvenience but can also be dangerous. There
are also applications where the presence of friction is an inconvenience, such as in
machines. Oil and other lubricants are used to reduce friction and make these devices run
more efficiently.
In this lab you will measure the force of friction that is present between different
surfaces and under certain conditions. It might seem rather a difficult thing to measure at
first, but it really isn’t.
Consider a block of wood being pulled across a table by a string attached to the block.
The block is being pulled at constant velocity. Let’s consider the forces on the block.
There is an applied force (by you) in the direction of motion. There is also a force of
friction that is opposing the applied force. How do these forces compare?
The key words in the above description are constant velocity. If you pull an object at
constant velocity, the object is not accelerating. By Newton’s Second Law, zero
acceleration implies zero net force. This means that the force of friction is exactly
matched by the applied force. The forces have equal magnitudes in opposite directions.
So we can measure the magnitude of the frictional force by finding the applied force that
will result in constant velocity as the block moves across the surface.
In this lab you will perform a series of short experiments in which you vary one
property of the two surfaces in contact and measure the force necessary to move an object
at constant velocity. By doing so you will be measuring the force of friction.
Procedure:
Set up the friction block or box with a spring scale. Record force as accurately
as possible throughout the experiment.
A. Nature of Surfaces
1.
Place the wood block on a piece of brown paper. Place the string around the block
so that when it is dragged the string will not interfere with the surface contact. Place a
mass or two on the block. Weigh the block and masses and record in Data Table A. Keep
them there throughout this part of the experiment.
2.
Practice until you can pull the block at constant velocity (when pulling at constant
velocity, the force reading will remain stable). Turn on the force sensor. Have your lab
partner take the force data while the block is in motion. Record the force in Data Table A.
Make sure you pull with the string in a horizontal position each time.
3.
Vary the surface by pulling the block on different types of paper. Repeat Procedure
Data Table A
Weight of block and masses = _______________ N
Types of surfaces in contact
Force (N)
Wood on brown paper
Wood on
Wood on
B. Area of Surfaces
1.
Place the wood block on a piece of brown paper. Place the string around the block
so that when it is dragged the string will not interfere with the surface contact.
2.
Pull the block at constant velocity. Have your partner read the data. Again place a
few masses on the block. Keep using the masses throughout this section in order to
remain consistent. Record your data in Data Table B.
3.
2.
Place the block so that a different side is in contact with the paper and repeat step
4.
Repeat step 3 with the third side of the block.
Data Table B
Side of block in contact with paper
Force (N)
Face
Side
End
C. Starting Motion vs. Maintaining Motion
1.
Place the block with its largest surface area in contact with the paper. Place a few
masses on the block.
2.
Pull the string with a slowly increasing force. Measure the force that it requires to
just start the block moving. Record in Data Table C. Then measure the force needed to
keep the block moving at a slow constant velocity. Record in Data Table C.
Data Table C
Motion
Starting
Sliding
Force (N)
D. Force Pressing Surfaces Together
1.
Measure the weight of the block. Record in Data Table D.
2.
For this part, use brown paper as a surface. Without any masses on the block,
measure the force necessary to move the block uniformly. Record.
3.
Place a mass on the block. Weigh, and record.
4.
Measure the force necessary to move the block and mass uniformly, and record.
5.
Add more mass to the block. Weigh and record. Measure the force necessary to
move the block and masses uniformly and record.
6.
Repeat and fill in the data table. If necessary, remove some masses to get
intermediate weights as well.
Data Table D
Weight (N)
Block
Block + Mass1
Block + Mass2
Block + Mass3
Block + Mass4
Block + Mass5
Block + Mass6
Analysis:
Applied Force (N)
1. Construct a graph of data from Data Table D. Plot Weight on the horizontal axis and
Applied Force on the vertical axis. If you are using a graphing program, do a regression
analysis and find the slope. If you are graphing the data by hand, estimate and draw a
best-fit line, choose two points, and determine the slope from the two points.
2. If the block in the lab is pulled with a constant velocity, then the applied force is
being used solely to overcome friction. So the y-axis data is really the force of friction Ff.
Also, the block is being pulled on a horizontal surface, so the weight is the same as the
normal force FN. The x-axis data is then FN. The slope is the ratio of Ff to FN. From your
regression analysis, what is the value for the slope of the line?
_______________
Questions and Conclusions:
1. From your results, the force of friction is dependent on which factor(s)?
2. From your results, the force of friction is independent of which factor(s)?
3. List three examples where friction helps you
4. List three examples where friction is a hindrance.
5. What quantity is indicated by the slope of the graph
6. Using the data from Data Table A ( the applied force and the weight of the block),
calculate the coefficient of friction m for each of the surfaces tested in Part A. Put all of
the calculations below .
7. From your graph, what is the coefficient of friction for wood on brown paper?
8. Consider three steel balls starting from rest. When an equal force is applied to each
ball, which of these actions could not take place on a frictionless surface? Explain.
(a)
sliding down an inclined plane with increasing velocity
(b)
(c)
rolling down an inclined plane with increasing velocity
sliding along a horizontal surface with constant velocity
NAME - _________________________CLASS BLOCK - _________
Quiz #2 - Newton’s Laws
Answer each question fully, showing all your work. Use units. Take your time, and enjoy! Remember:
F = ma, a =
F
, W = mg, g = 9.8 m/s2, Ff = FN. (I think that does it!)
m
1/ For the following examples, identify which of Newton's three Laws of Motion best
describes the situation, and write 1st, 2nd, or 3rd in the blanks at left. (5 pts. ea.)
_____ a. As Mr. Coleman sped off in his Beetle, the mug of coffee on the dashboard slid
back and spilled all over the passenger seat.
_____ b. With her lightweight racing shoes on, Becca was able to accelerate
around the track much faster.
_____ c. Mr. Smith and his kids row out into Lake Champlain, the oars pushing against
the water and the water pushing back to propel the dinghy across the lake.
_____ d. Chana pushed the toboggan full of kids across the snow. When two of them
fell out, the toboggan sped up, though she continued to push with the same force.
2/ Let’s say your school backpack (with all your books, papers, pencils, and snacks) has
a total mass of 8.5 kg. What would be the mass of your backpack if it were taken to
Saturn, where the gravitational acceleration averages 25.0 m/s2, 2½ times that of Earth? (5
pts.)
3/ Craven Morfizz has a new motorcycle that weighs 2450 N. What is its mass in
kilograms? (5 pts.)
4/ The original mass of a rocket is 50,000 kg; it accelerates off the launch pad at a rate of
12.0 m/s2. By the time it reaches the outer atmosphere, the rocket has burned up most of
its fuel, and has only 1/10 of its original mass, but the force exerted by the engines is the
same. What is the rocket's new acceleration? (5 pts.)
5/ A towchain is used to haul a 1950-kg SUV, giving it an acceleration of 1.35 m/s2.
What force does the chain exert on the SUV? (5 pts.)
6/ A person weighing 490 N stands on a scale in an elevator.
a/ What does the scale read when the elevator is at rest? (2 pt.)
b/ What does the scale read when the elevator climbs at a constant velocity? (2 pt.)
c/ The elevator slows down at a rate of 2.2 m/s2 as it reaches the desired floor. What
does the scale read? (3 pts.)
7/ A force of 20 N accelerates a 9.0 kg scooter at 2.0 m/s2
along the sidewalk.
a/ How large is the frictional force? (2 pts.)
b/ What is the coefficient of friction? (1 pt.)