Download Forces Packet

Unit 3
Forces Part 2
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Vocabulary:
Force
Acceleration
Mass
Net Force
Balanced Forces
Unbalanced Forces
Friction
Air resistance
Gravity
Weight
Inertia
Action Force
Reaction Force
Concepts:
How does a force affect an object’s motion?
How does force affect acceleration?
How does mass affect acceleration?
How do you find the net force acting on an object?
How does friction affect an object’s motion?
How does air resistance affect an object’s motion?
How does gravity affect an object’s motion?
How does gravity affect an object’s mass?
How does gravity affect an object’s weight?
How does mass affect an object’s inertia?
How do action and reaction forces compare?
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Anticipation Guide: How Seat Belts Work
Directions # 1:
1. Before you read the article, read each statement below.
2. If you agree with the statement, place a check mark in the Agree column.
3. If you disagree with the statement, place a check mark in the Disagree column.
a. This section will not be graded for correct answers.
b. The purpose of this section is to activate what you already know about how seat
belts work.
Agree
Disagree
Statement on Seat Belts
1. The property of matter which seatbelts are based on is inertia.
2. Inertia is every object’s freedom to move.
3. Air resistance and friction are forces which act with inertia.
4. Without a seat belt, a rider’s inertia is independent of the
car’s.
5. A person can be killed by flying head first through a
windshield because the head is a large, sturdy part of the
body.
6. It is important to use the lap belt and shoulder belt to spread
out the force exerted on your body.
7. Wearing a seat belt makes the rider’s inertia the same as the
car’s.
8. Crumple zones are designed to make the crash look worse.
9. A crumple zone can only do its job if a rider is wearing a seat
belt.
10. Wearing a seat belt prevents riders from flying out of a
windshield because they will stop when the car stops.
4. Read the article “How Seat Belts Work”..
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How Seatbelts Work
by Tom Harris
According to a research report from the
National Highway Traffic and Safety
Administration, seatbelts save approximately
13,000 lives in the United States each year.
Furthermore, the NHTSA estimates that 7,000
U.S. car accident fatalities would have been
avoided if the victims had been wearing belts.
According to the NHTSA, seatbelts reduce the
risk of death for a front seat car occupant by
about 50 percent.
When you think about it, this is absolutely
amazing: How can a piece of fabric end up
being the difference between life and death?
What does it actually do? In this article, we'
ll examine the technology of seatbelts to see
why they are one of the most important technologies in any car.
Crashing Concepts
The basic idea of a seatbelt is very simple: It keeps you from flying through the windshield
or hurdling toward the dashboard when your car comes to an abrupt stop. But why would
this happen in the first place? In short, because of inertia.
Inertia is an object'
s tendency to keep moving until something else works against it. To put
it another way, inertia is every object'
s resistance to changing its speed and direction of
travel. Things naturally want to keep doing what they are doing, whether it be moving or
staying at rest.
If a car is speeding along at 50 miles per hour, inertia wants to
keep it going 50 mph in one direction. Air resistance and
friction with the road are constantly slowing it down, but the
engine'
s power compensates for this energy loss.
Anything that is in the car, including the driver and
passengers, has its own inertia, which is separate from the
car'
s inertia. The car accelerates riders to its speed. Imagine
that you'
re coasting at a steady 50 miles per hour. Your speed
and the car'
s speed are pretty much equal, so you feel like
you and the car are moving as a single unit.
But if the car were to crash into a telephone pole, it would be obvious that your inertia
and the car'
s were absolutely independent. The force of the pole would bring the car to
an abrupt stop, but your speed would remain the same. Without a seatbelt, your inertia is
independent of the car’s, and you would either slam into the steering wheel at 50 miles
per hour or go flying through the windshield at 50 miles per hour.
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It is a given that no matter what happens in a crash, something would have to exert force
on you to slow you down. But depending on where and how the force is applied, you
might be killed instantly or you might walk away from the damage unscathed.
If you hit the windshield with your head, the stopping power is concentrated on one of the
most vulnerable parts of your body. It also stops you very quickly, since the glass is a hard
surface. This can easily kill or severely injure a person.
A seatbelt is made of softer materials that give and stretch. It also applies the stopping
force to more durable parts of the body over a longer period of time. In the next section,
we'
ll see how this reduces the chances of major injury.
Taking a Hit
In the last section, we saw that any time a car comes to a sudden stop, a passenger
comes to a sudden stop as well. A seatbelt'
s job is to spread the stopping force across
sturdier parts of your body in order to minimize damage.
A typical seatbelt consists of a lap belt, which rests over your pelvis, and a shoulder belt,
which extends across your chest. The two belt sections are tightly secured to the frame of
the car in order to hold passengers in their seats. This ties passengers to the car, essentially
making their inertia the same as the cars’ inertia.
When the belt is worn correctly, it will apply most of the
stopping force to the rib cage and the pelvis, which
are relatively sturdy parts of the body. Since the belts
extend across a wide section of your body, the force
isn'
t concentrated in a small area, so it can'
t do as
much damage. Additionally, the seatbelt webbing is
made of more flexible material than the dashboard or
windshield. It stretches a little bit, which means the stop
isn'
t quite so abrupt. Safe seatbelts will only let you shift
forward slightly.
A car'
s crumple zones do the real work of softening the
blow. Crumple zones are areas in the front and rear of
a car that collapse relatively easily. Instead of the
entire car coming to an abrupt stop when it hits an obstacle, it absorbs some of the
impact force by flattening, like an empty soda can. The car'
s cabin is much sturdier, so it
does not crumple around the passengers. It continues moving briefly, crushing the front of
the car against the obstacle. Of course, crumple zones will only protect you if you move
with the cab of the car -- that is, if you are secured to the seat by your seatbelt.
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Directions # 2:
1. Re-read the statements above.
2. If the information in the article supports your choice, place a check mark in the
“Supported” column. (The statement # s are the same in both charts.)
a. Write the paragraph number of where you found the support.
b. Quote the article for evidence of support.
3. If the information in the article does not support your choice, place a check mark in
the “Not Supported” column.
a. Write the paragraph number of where you found the correct information.
b. Quote the article for evidence.
Supported
Not
Supported
Parapraph #
Quote From Text
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Information: Newton’s 1st Law
Directions: Read pg 349-350 in your text book. Use the space below to write down
important ideas about inertia and Newton’s 1st Law of Motion. We will compile notes on
the next page together.
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Inertia and Mass
1. What is inertia?
2. What does inertia have to do with mass?
3. As the amount of _____________ increases, the inertia of the object
____________________.
Newton’s 1st Law of Motion
4. What is Newton’s 1st Law of motion?
5. What does that mean in plain english?
6. Give four examples of Newton’s 1st Law from “real” life.
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First Law Problems
1. How is it possible that an object is not moving when there could be multiple forces
acting on it all at once?
2. What is INERTIA?
3. What type of things have the most inertia?
4. The law of inertia states that no force is required to maintain motion. Why then do
you have to keep pedaling a bicycle to maintain motion?
5. Many automobile passengers have suffered neck injuries when struck by cars from
behind. How does Newton’s first law of inertia apply here?
6. How do headrests help guard against this type of injury?
7. Compare and contrast the following pairs of words
a. balanced force & net force
b. force & inertia
c. force & net force
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8. Which term below best describes the forces on an object with a net force of zero?
a. inertia
b. balanced forces
c. acceleration
d. unbalanced forces
9. What is the tendency for an object to resist any change in its motion?
a. net force
b. balanced force
c. acceleration
d. inertia
10. Explain why a passenger who is not wearing a safety belt will likely hit the windshield
in a head-on collision.
Teacher’s
Initials
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Inquiry Lab: Newton’s Second Law
State the Problem
How does mass affect an object’s tendency to accelerate, when the same force is
applied?
Pre-lab: In this experiment…
1. What was your independent variable? __________________________________________
2. What was your dependent variable? ___________________________________________
3. Name at least two constants in this experiment. _________________________________
4. Why will we repeat this experiment and find the average distance traveled?
Write a Hypothesis
Design an Experiment
Materials
•
•
Tennis
ball
Ring
Stand
•
Tennis ball with
eyescrew
•
Meter stick
•
Styrofoam ball
•
Electronic
Balance
•
75 cm string
Procedure
1. ____Measure the mass of the tennis ball and Styrofoam ball. Record this data in the
data table.
2. ____Tie one end of the string to the ring stand and the other end to the eyescrew on
the tennis ball.
3. ____Set the ring stand on a table. Adjust the height of the ball so that it hangs
barely above the surface of the table.
4. ____Place the Styrofoam ball at the edge of the table. Adjust the position of the
ring stand so that when the tennis ball is swung, it will contact the Styrofoam ball
and knocks it off the table.
5. ____Hold the tennis ball so that it is perpendicular to the table and release it so that
it hits the Styrofoam ball.
6. ____Mark on the floor where the ball lands.
7. ____Measure the distance the table to the place where the ball landed.
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8. ____Repeat 4 more times and find the average distance the Styrofoam ball
traveled.
9. ____Repeat steps 1-8, but use a tennis ball in place of the Styrofoam ball.
Run the Experiment & Collect Data
Mass of tennis ball and eyescrew:
______________________
Table 1: Distance Traveled by Styrofoam Ball
Mass of
Distance
Distance
Distance
Styrofoam
(m) Trial 1
(m) Trial 2
(m) Trial 3
Ball (g)
Distance
(m) Trial 4
Distance
(m) Trial 5
Average
Distance
(m)
Table 2: Distance Traveled by Tennis Ball
Mass of
Distance
Distance
Distance
Tennis Ball
(m) Trial 1
(m) Trial 2
(m) Trial 3
(g)
Distance
(m) Trial 4
Distance
(m) Trial 5
Average
Distance
(m)
Analyze the Data
1. Was your hypothesis correct? Explain using data.
2. Were there any errors? Explain.
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3. How does increasing the mass affect the object’s motion when the force is the
same?
4. Explain the difference in the distance traveled by the two balls (which went further).
5. How does this relate to Newton’s Second Law?
6. Explain the relationship between mass and acceleration if the force is held
constant. _______________________________________________________________________
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Information: Mass, Force, and Acceleration – Newton’s 2nd Law
Force, mass and acceleration have a close relationship. This relationship is described in
Newton’s second law of motion. The law states that the force acting on an object is
equal to the object’s mass multiplied by the object’s acceleration. An object will
accelerate (move) in the direction of the net force.
For instance, the net force on the object below is acting to the right, so the object will
move to the right!
60 N
43 N
Movement (net force = 17 N)
The force on an object can be calculated using the mass of the object and the
acceleration of the object.
THINK: If you have two soccer balls of the same mass and you toss one underhand and
you throw the other as hard as you can, which one will accelerate faster?
________________________________________
o The greater the acceleration of the object, the greater the force acting on the
object must be.
THINK: If you have two objects of different mass, and you apply the same force to them
both which one will accelerate faster, the heavy one or the lighter one?
____________________________________
o The greater the mass of the object, the greater the force acting on the object must
be.
Critical Thinking Questions:
1. What is the relationship between force and acceleration?
2. As force increases, the acceleration ________________________.
3. How does the acceleration of an object affect the distance traveled?
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4. What is the relationship between force and mass?
5. As mass increases, the force must ________________________.
6. What two variables does force depend on?
7. Write an equation that you could use to calculate the force on an object.
Teacher’s
Initials
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2nd Law Problems
Directions: Answer the following problems about Newton’s second law.
1. What is the mass of a wagon accelerating at 4 m/s2 if the force required to pull it is
120 Newtons?
Givens
Solving For
Equation
Substitution
Answer with Units
2. An Olympic swimmer pushes through the water with a force of 35 Newtons. What is
her acceleration if she has a mass of 70 kg?
Givens
Solving For
Equation
Substitution
Answer with Units
3. A rock is dropped off the edge of a cliff so that it accelerates down at 9.8 m/s2.
What is the force acting on the rock if its mass is 5 kg?
Givens
Solving For
Equation
Substitution
Answer with Units
4. A net force of 10 N is applied to an object having a mass of 2 kg. What is the
acceleration of the object?
Givens
Solving For
Equation
Substitution
Answer with Units
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5. A net force of 20 N is applied to an object having a mass of 2 kg. What is the
acceleration of the object?
Givens
Solving For
Equation
Substitution
Answer with Units
6. In questions 4 and 5 above, the mass of the object stayed the same. The net force
applied to the object doubled. As the net force doubled, the acceleration
____________________________. This is because net force is __________________________
to acceleration according to Newton’s Second Law.
7. A net force of 20 N is applied to an object having a mass of 4 kg. What is the
acceleration of the object?
Givens
Solving For
Equation
Substitution
Answer with Units
8. In questions 5 and 7 above, the force applied to the object was help constant. The
mass of the object was doubled. As the mass doubled, the acceleration
______________________________. This is because mass is ____________________________
to acceleration according to Newton’s Second Law.
9. What acceleration will result when a 12 N net force is applied to a 3 kg object?
Givens
Equation
Solving For
Substitution
Answer with Units
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Information: Newton’s 3rd Law – Action & Reaction
Directions:
1. Read pages 353 - 359.
2. Use the space below to write down important ideas about Newton’s 3rd Law.
Including but not limited to:
a. Action force
b. Reaction force
c. Newton’s 3rd law
d. How does mass affect the reaction to the forces?
e. How do action reaction forces compare to each other?
3. Complete the Sequential Alphabet Roundtable on the next page.
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Sequential Alphabet Roundtable – Newton’s 3rd Law
Directions: Read the section in your text about Newton’s 3re Law. Fill in each square with a main idea, phrase, or word
that SPECIFICALLY has to do with the 3rd Law. The main idea, phrase, or word MUST START WITH THE LETTER IN THE BOX.
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z
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3rd Law Problems
1. What is Newton’s 3rd Law of Motion?
2. Draw a picture of an action/reaction pair of forces.
3. Why don’t action and reaction forces cancel?
4. Explain whether there can be any forces acting on a car moving in a straight line
with a constant speed.
5. Explain why when you pull a door open, you don’t move if the force on the door
and you are the same?
6. I push on a wall with a force of 20 N. What are the magnitude and direction of the
reaction forces? Draw the reaction force and explain in words.
20 N
7. A mosquito flies along and runs into the windshield of a rapidly moving vehicle.
Which force is stronger: the force of the windshield hitting the mosquito or the force
of the mosquito hitting the windshield? Why?
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8. Complete the follow action/reaction pairs by drawing in the forces:
a. A tennis ball pushes a racket
c. A pool stick pushes the cue
ball
b. A soccer player strikes a ball
d. A weightlifter pushes up on a
dumbbell
9. A gun recoils when it is fired. The recoil is the result of action-reaction force pairs. As
the gases from the gunpowder explosion expand, the gun pushes the bullet
forwards and the bullet pushes the gun backwards. The acceleration of the
recoiling gun is ... (circle one):
a. greater than the acceleration of the bullet.
b. smaller than the acceleration of the bullet.
c. the same size as the acceleration of the bullet.
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10. In the top picture (below),
a physics student is pulling
on a rope which is
attached to a wall. In the
bottom picture, the
physics student is pulling
upon a rope which is
attached to an elephant.
In each case, the force
scale reads 500 Newtons.
The physics student is
pulling (circle one):
a. with more force when the rope is attached to the wall.
b. with more force when the rope is attached to the elephant.
c. the same force in each case
11. Identify the at least six pairs of action/reaction forces in the picture below:
a. ______________________________________________________________________
b. ______________________________________________________________________
c. ______________________________________________________________________
d. ______________________________________________________________________
e. ______________________________________________________________________
f. ______________________________________________________________________
12. An elephant and a mouse would both have a weight of 0 N in gravitational-free
space. However, they would still retain their “amount of matter” or
__________________. If they were moving toward you with the same speed, would
they bump into you with the same affect? Why?
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Pop Rocket Demo
1. What happens when baking soda and vinegar are mixed together?
2. How do you know that?
3. What happened to the film canister? Explain why this happened.
4. Can you think of another event where pressure causes a similar "explosion?"
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