Download Forces Packet

Unit 3
Forces Part 1
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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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Introduction to Forces Stations
Directions: There are six stations in the classroom. Each station is an investigation on force
and motion. There is a task card at each station with directions. Read the task card
carefully, and then do the activity.
Please, stay at the station until you are asked to move by your teacher.
Station #1: Measuring Force
Background
Forces are pushes or pulls. If forces are unbalanced, they make objects move or stop
moving. Forces are measured in Newtons (N). A Newton is the amount of force necessary
to accelerate one kilogram of mass at a rate of 1 m/s2 (N = kg*m/s2). A Newton is a kg x
m/s2.
Weight is the downward force on an object due to the acceleration of gravity. It is
properly measured in Newtons (N).
Data
Mass (g)
Force needed to move
(N)
1. What relationship do you see between mass and force?
2. Mass and force have a _____________________________
relationship. The ___________ mass an object has, the
_______________ force needed to move it.
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Station #2: Friction
Background Information
Friction is a force that resists the motion of an object. That means that friction slows
objects down. Friction results from the close contact of two surfaces that are sliding across
each other. When you slam on your brakes and your car skids to a stop with locked
wheels, it is the force of friction that brings it to a stop. Friction resists the car’s motion.
Friction is caused by irregularities (bumps and holes) in the surface of objects that are
touching.
Data
Surface
Force Needed to Move Block
(N)
Air (Lifted off table)
Plain Table
Wax Paper
Plastic Wrap
Light Sand Paper
Heavy Sand Paper
1. What is the relationship between the type of surface and the amount of force
needed to move the object?
2. Explain.
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Station #3: Gravity
Background Information
There is a specific type of acceleration that affects everything on Earth is gravity. Gravity
is a very specific acceleration that acts at a distance and pulls objects toward each
other. The amount of matter in an object is called its mass. The force that gravity exerts
on an object depends on the amount of mass the object has. The weight of an object is
the measurement of the force of gravity on that object. You weigh something on a scale,
according to the force that the Earth pulls it down. So the weight is actually the force of
gravity on that object.
If you drop an object, it will speed up because of acceleration due to gravity.
Data
Time for Whirly Bird to Fall (sec)
Trial 1
Trial 2
Trial 3
Average
Naked Whirly
Bird
Whirly Bird
+ 1 paper clip
Whirly Bird
+ 2 paper clips
Whirly Bird
+ 3 paper clips
1. Did the mass of the paper Whirly Bird make any significant difference in the time it
took to fall? Why or why not?
2. Can you think of something the mass of the Whirly Bird would affect in this
experiment? What do you think it is?
Information: Forces
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When you ride a bike, your foot PUSHES against the pedal.
The push makes the wheels of the bike move.
When you drop something, it is PULLED to the ground by gravity.
A PUSH or a PULL is a FORCE. So, a good definition for force is a
push or pull in a particular direction.
Forces can affect motion in several ways:
• They can make objects start moving.
• They can make objects move faster.
• They can make objects move slower.
• They can make objects stop moving.
• They can make objects change direction.
• They can make objects change shape.
Since forces cause changes in the speed of an object, we can say that forces cause
acceleration!!!
Remember, a = s/t. So, if the speed is changed, there is
acceleration.
FORCE FACTS:
• Forces are measured in Newtons (N)
• Forces act in pairs
• Forces act in a speciific direction
• Forces usually cannot be seen, but their effects
can
Critical Thinking Questions:
1. Define force.
2. Give an example of a force from the reading.
3. Explain how forces cause acceleration.
4. What unit are forces measured in?
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Put it to Use
Directions:
1. In the blank boxes write PUSH or PULL to label the kind of force each picture
represents.
2. Draw an arrow in the direction of the push or pull ON each picture.
Teacher’s
Initials
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Information: Forces
More than one force can act on an object at a time. Forces can exert a push or pull in
any direction. What happens to the object depends on two things:
1. The strength of the forces
2. The direction of the forces
When more than one force acts on an object, the forces combine to form a NET FORCE.
This is just like the net pay from your paycheck. You may have earned $500, but the
Federal, State and Medicare taxes work in the opposite direction to reduce the amount of
your paycheck. These amounts combined equal your NET PAY.
The combination of all the forces acting on an object is a net force.
• Forces may work together or they may be opposite forces.
o Forces that work together are working in the SAME DIRECTION.
When two forces act in the same direction on an object, the net force
is equal to the SUM of the two forces.
o Forces that are working against each other are working in OPPOSTIE
DIRECTIONS.
When two unequal forces act in opposite directions on an abject, the
net force is the DIFFERENCE of the two forces, and the net force is in the
direction of the greater force.
If two forces of equal strength act on an object in opposite directions, the forces will
cancel. This results in a net force of zero and no movement. Two or more opposite forces
are balanced (or equal) forces if their effects cancel each other and they do not cause a
change in an object’s motion.
If the effects of the forces don’t cancel each other, if one force is stronger than others, the
forces are unbalanced forces. Unbalanced forces cause a change in motion; speed
and/or direction.
•
Forces may be balanced or unbalanced.
Type of Force
Direction
Balanced
Opposite
Unbalanced
Opposite
Strength (# Value)
Equal
Unequal
o Balanced forces have the same strength (numerical value).
o Unbalanced forces do not have the same strength (numerical value).
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Critical Thinking Questions:
#1
The two forces shown here are working in the same
direction.
1. Circle One:
These forces are (working together) OR (not working
together).
2. How do you find the net force of these two forces?
#2
The two forces shown here are working in opposite
directions.
1. Circle One:
These forces are (working together) OR (not working
together).
2. How do you find the net force of these two forces?
3. Are these forces balanced or unbalanced? ______________________________________
4. Explain.
.# 3
The two forces shown here are working in opposite
directions.
1. Circle One:
These forces are (working together) OR (not working
together).
2. How do you find the net force of these two forces?
3. Are these forces balanced or unbalanced? ______________________________________
4. Explain.
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5. If the net force on an object is 0, what will be the direction of motion?
6. What are the two characteristics of forces that can affect an object?
7. When forces act in the same direction, how does one find the net force?
8. When forces act in opposite directions, how does one find the net force?
9. Explain balanced forces. How do they affect the motion of an object?
10. Explain unbalanced forces. How do they affect the motion of an object?
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Put it to Use
Directions: Circle the best answer in bold from the statements below.
1. The forces shown above are Pushing / Pulling forces.
2. The forces shown above are Working Together / Opposite Forces.
3. The forces are Equal / Not Equal.
4. The forces Do / Do Not balance each other.
5. The net force is 1000 N to the Right / 1000 N to the left / Zero.
6. There Is / Is No motion.
1. The forces shown above are Pushing / Pulling forces.
2. The forces shown above are Working Together / Opposite Forces.
3. The forces are Equal / Not Equal.
4. The forces Do / Do Not balance each other.
5. The stronger force is pulling to the Right / Left.
6. The weaker force is pulling to the Right / Left.
7. Motion is to the Right / Left.
Teacher’s
Initials
11
Information: Everyday Forces (Friction & Gravity)
Friction is a force that resists the motion of an object.
That means that friction slows objects down. Friction
results from the close contact of two surfaces that are
sliding across each other. When you slam on your
brakes and your car skids to a stop with locked wheels,
it is the force of friction that brings it to a stop. Friction
resists the car’s motion.
Even when you gently apply the brakes, it is the friction
between the brake pads that slow down the wheels,
which slows down your car. Friction resists the car’s
motion.
Air molecules hitting you can cause friction that will slow you down. Think about when you
run in gym class. If the wind is blowing at you, isn’t it harder for you to run? That is
because of the resistance the air molecules cause when they hit you – that’s air resistance
OR friction from air molecules.
Friction is caused by irregularities (bumps and holes) in the surface of objects that are
touching. Friction is represented by Ff (Force of friction).
o Review the results of the friction station from the first day.
What is the relationship between the type of surface and the amount of force needed to
move across the surface?
If you were to push the box below with a force in the direction of the arrow, which way
would the force of friction be acting? Draw the arrow.
Your force
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There is a specific type of acceleration that affects
everything on Earth is gravity. Gravity is a very specific
acceleration that pulls objects toward each other. It is
represented by the variable “g” and because it is
acceleration it is measured in units of m/s2. Earth’s
gravity is 9.8 m/s2. The gravity of Earth pulls all objects
on the surface toward the center of Earth. The force
that gravity exerts on an object depends on the
amount of mass the object has – this is the weight of an
object. Earth’s gravity is constant and pulls all objects
with an acceleration of 9.8 m/s2. The moon’s
gravitational force is 1.6 m/s2, and Mars pulls objects
toward it with a force of 3.8 m/s2. If you were to visit
these two other celestial bodies, your weight would
change according to the acceleration on them.
If you drop an object, it will speed up because of acceleration due to gravity.
o Look back at the whirly bird station from the first day.
How did gravity affect the speed of the dropped objects?
Does the mass of an object make a difference in the time it takes to fall? Why or why not?
Information: Gravity Gives You Weight
How much do you weigh? What is your mass? Many people think that these two
questions are asking the same thing. But that’s not true. Weight and mass are different.
Although many people know what their weight is, few know their mass.
Weight is a measure of the force of
gravity pulling on a body. It is the
measure of the force your body exerts on
the ground. If you weigh 400 Newtons
(90 pounds), then gravity pulls you down
toward the earth with a force of 400
Newtons. You can measure your weight
by standing on a bathroom scale. When
you stand on the scale, your body’s
weight compresses the spring in the
scale. The amount the spring is
compressed is proportional to your
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body’s weight. If you went to the moon, you would weigh less because the force of
gravity on the moon’s surface is not as strong as the force of gravity on the surface of the
earth. In fact, on the moon, you would weigh only one-sixth as much as on the earth.
Weight depends on how much mass an object has and how much gravity is acting on the
object. It is represented by the variable “w” and is measured in Newtons (N). As gravity
increases, so does weight – they have a proportional relationship. As mass increases, so
does weight – they have a proportional relationship.
Now what about your mass? Mass is a measure of how much matter is in your body. The
mass of a person who weighs 400 Newtons on the earth is about 40 kilograms. Mass is
measured differently from weight. Mass is measured in kilograms. You can measure your
mass by sitting on a balance. Suppose you went to the moon. Would your mass change?
The answer is no – the matter in your body would be the same as it is on the earth. If you
do not add to or take away any matter from your body, your mass stays the same, no
matter where you are.
Critical Thinking Questions
1. Write a proportional relationship between your weight and how much the springs of
a scale would be pushed down.
2. What would a 6000 N car weigh on the moon? ___________________________________
3. What would my mass be on the moon if it were 55 kg on the earth? _______________
4. What is mass a measurement of?
5. Weight takes into consideration the amount of _____________________________ and
________________________.
6. Name two variables needed to calculate weight.
7. Write an equation for weight using these variables and the information above.
Teacher’s
Initials
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Put it to Use
Weight and Mass Problems
1. Convert 100 grams to kilograms? _______________________________________
2. Convert 100 kilograms to grams? _______________________________________
3. If a specific gravity is not given in the problems below, you can safely assume the
gravity is that of Earth’s. What is Earth’s gravity? ______________________
4. Find the weight of a brick with a mass of 1.3 kg.
Givens
Solving For
Equation
Substitution
Answer with Units
5. What is the weight of a bicycle with a mass of 20 kg?
Givens
Solving For
Equation
Substitution
Answer with Units
6. What is the weight of a 330 g can of diet soda?
Givens
Solving For
Equation
Substitution
Answer with Units
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7. If a large book has a weight of 9.1 N, what is its mass?
Givens
Solving For
Equation
Substitution
Answer with Units
8. Explain why Jupiter’s gravity is greater than the Earth’s, but the Moon’s gravity is less
than the Earth’s.
9. A rocket travels to the Moon and drops a land rover down to the surface. The
acceleration due to gravity is about 1.6 m/s2 on the Moon. What is the land rover’s
weight if it has a mass of 4000 kg?
Givens
Solving For
Equation
Substitution
Answer with Units
Teacher’s
Initials
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Bill Nye “Friction”
Directions: Use the information from Bill Nye “Friction” to answer the following questions.
Make sure to answer in full and complete sentences.
1. What is friction according to Bill Nye?
2. The _________________________________ things are rubbing together, the
_____________________________ friction there is.
3. Friction turns the energy used to ___________________________ into
__________________.
4. What does friction have to do with knots?
5. Why do you have fingerprints? What do fingerprints have to do with friction?
6. How does the motion of a hovercraft involve friction?
7. What happens to your feet as you water ski on your bare feet? Why?
8. Why does a slide have aluminum plates on it?
9. How does friction help a BMX rider?
10. Why doesn’t the square bowling ball work very well?
11. Why must there be some friction between train tracks and train wheels?
12. How does a slug use its mucous?
13. How was friction responsible for the loss of the space shuttle Columbia?
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