Download Forces (Dynamics) – Notes Day 1

Name ______________________-
Date _____________________________
Forces (Dynamics) – Notes Day 1
1. A force is defined as ___________________
a. What is it the result of?
b. The units for force are _____________________
c. It is a _________________ quantity which means it has ____________________
and ________________________
d.
What is the sum of multiple forces on an object called?
e. What is a practical example of two or more forces acting on an object at the same
time to produce a “resultant”?
Types of Forces
a. Gravity (
)
a. Is____________________ between two objects
b. Gravity between an object and Earth (or any planet for that matter is called
_______________
i. So, does gravity “push down” or “pull toward”????
c. If gravity exists everywhere, why don’t two masses attract each other like
magnets?
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Name ______________________b. Friction (
Date _____________________________
)
a. Is the _____________________ that acts when an object moves or
ATTEMPTS to move across a ____________________
b. What factors affect friction?
c. Air Resistance (
)
a. The type of friction that occurs when _____________________________
b. What causes this type of friction?
d. Tension (F
a.
)
__________________ transmitted through a rope, wire, or string when it
is ____________________ from __________________ends
b. Is tension higher when you are closer to the object (person) creating the
tension?
e. Normal Force (
)
a. ______________________ exerted on an object which is in contact with
another stable object or surface
f. Applied Force (
)
a. Force ________________________ by a _______________ or an object.
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Name ______________________-
Date _____________________________
NEWTON’S FIRST LAW
What is Newton’s First Law? (yes you need to write the WHOLE THING)
NEWTON”S FIRST LAW…cont.
So what does this law mean?
If an object is at rest and all the forces are balanced…
If an object is at rest and the forces are NOT balanced…
If an object is in motion and all forces are balanced….
If an object is in motion and all forces are NOT balanced….
SUMMARIZE NEWTON’s FIRST LAW HERE:
NEWTON’S FIRST LAW IS ALSO CALLED
________________________________________________________-
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Name ______________________-
Date _____________________________
Inertia is:
a.
b.
c.
A CHART COMPARING MASS VS. WEIGHT
MASS
WEIGHT
Definition
amount of matter in an object
FORCE of GRAVITY
Units
kg
N
Variation?
CONSTANT
NEVER CHANGES
Depends on elevation
Varies by planet
Measured with
balance
scale (springs)
LINK:
Weight = Mass x Acceleration due to Gravity
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On Earth, accel. due to gravity = -9.8 m/s
WHAT IS A FREE BODY DIAGRAM?
Standard representation of the relative ______________________________
of all forces acting upon an object.
The object is represented by a _________________
The forces are represented by ___________________
Size of the arrow reflects :_______________________________
Direction of the arrow shows _____________________________
Each arrow is labeled to ___________________________________
Arrows are always drawn ___________________________________
Must depict all the forces which act on the object
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Name ______________________-
Date _____________________________
 Vector addition considers different directions
 Same direction: add
 Opposite direction: subtract
 What about at right angles?
 What about at obtuse or acute angles?

PROBLEMS
 The net force is known for each situation below.
 However, the magnitudes of a few of the individual forces are not known.
 Analyze each situation individually and determine the magnitude of the
unknown forces.
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Name ______________________-
Date _____________________________
Newtons Second Law of Motion
1. The ________________ of a body is _________________________________ to the
____________________ acting on the body and______________________________
to the mass.
2. What does directly proportional mean?
It means as force increases the acceleration___________________________
(as long as the mass remains constant)
3. What does inversely proportional mean?
As mass increases the acceleration _____________________(as long as the force
remains constant).
F
1
a  net
m
m
If standard units (kg, m/s 2 , and N) are used :
a  Fnet
a
Fnet
m
a
or,
Fnet  m  a
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Name ______________________-
Date _____________________________
The following apply to both the Second and Third Laws of Motion
Newton’s Second Law of Motion (problems)
Basic Problem Solving:
 What is the net force acting on a 5 kg crate that is accelerating at 3 m/s2?
 Advanced Problem Solving:
A 75 N applied force causes a 10 kg crate to accelerate to the right at 5 m/s2. What is the
force of friction acting on the crate?
 Draw a free body diagram first!
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Name ______________________-
Date _____________________________
Newton’s Third Law of Motion : Write it down
What does this mean?
What is an action:
What is a reaction:
Action and reaction “pairs“ are equal in _______________________, but
_______________ in ______________________.
These forces make an ______________________________________
 These forces MUST OCCUR _____________________________.
Newton’s Third Law of Motion
 Do the forces in an Action-Reaction Force Pair “cancel out”?
 No…



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Name ______________________-
Date _____________________________
 See Action/Reaction PAIRS AT THE SAME TIME
Recreate the next slide below. Look at where things are reversed.
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Name ______________________-
Date _____________________________
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