Name:
__________________________________________
Forces
Unit Packet
CP Physics
Ms. Morrison
Period:
_____
Notes/Diagrams
Additional Notes/Examples
Notetaking
Four Universal Forces:
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 NOTE: contact between objects is not
necessary as some forces will act over a
distance
Gravitational Force:
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Electromagnetic Force:
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Strong Nuclear Force:
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Weak Force:
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Additional Notes/Examples
Notetaking
Equilibrium Forces:
 concurrent forces:
 resultant force =
 when all external forces acting on an
object cancel out:
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Equilibrium:
 State of equilibrium –
 For concurrent forces acting on
object:
 Equilibrant force:

Friction:
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Additional Notes/Examples
Notetaking
Causes of Friction:
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Two Types of Friction:
 Static –
 Sliding –
 NOTE:
Friction Depends On:
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Coefficient of Friction:
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 NOTE:
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Additional Notes/Examples
Notetaking
Friction & Horizontal Motion:
 Two scenarios for horizontal motion
and the effects of friction:
 Object moves w/Constant Velocity
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 Object moves w/Acceleration
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Friction & Constant Velocity:
 free body force diagram –
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 since
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Friction & Acceleration:
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Additional Notes/Examples
Notetaking
Vertical Motion – Net Force:
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Vertical Motion:
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Forces on Inclined Planes:
 center dot =
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 weight vectors – two components
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Additional Notes/Examples
Notetaking
Forces on Inclined Planes:
 as angle of incline () increases:
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
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 as angle approaches 90o, acceleration
increases to 9.8 m/s2


CP PHYSICS
EQUILIBRIUM FORCES DEMO
Name: ________________________________
__ period
What is the mass of the weight? _____________
When both strings are placed on one spring scale and the second spring scale is attached to
the top of the first spring scale, what does each spring scale read? ________________
When the two strings are side by side, what does each spring scale read? ____________
What do the spring scales read when the two strings are pulled apart and make a right angle
to each other? _____________
Draw a vector diagram below of the spring scales and weight:
What is the downward force? __________
The two forces at a right angle to each other are the tension of the strings. The resultant of
these two forces is the upward force.
Calculate the resultant of the string tensions using the Pythagoream theorem:
The resultant tension from the strings is equal to the weight. It acts as the equilibrant force
because it is equal in magnitude to the weight but acts in the opposite direction. Therefore,
there is no net force acting on the mass.
Remember: When the net force is zero, according to Newton’s 1st law, the object is either at
rest or moving at constant velocity in a straight line.
Equilibrium Problems:
1.
A net force of 55 N acts due west on an object. What added single
force on the object produces equilibrium?
CP PHYSICS, EQUILIBRIUM FORCES DEMO, page 2
2.
Two forces act on an object. One force acts at 6.0 N horizontally. The second force
acts at 8.0 N vertically.
a. Find the magnitude and direction of the resultant force.
(Done using the parallelogram method.)
b. If the object is in equilibrium, find the equilibrant force.
Review Questions:
1.
What is meant about the forces acting on a book if we state that the
book is in equilibrium?
2.
How can the equilibrant of two or more forces be found?
3.
Can an object in equilibrium be moving? Explain.
4.
What is the net force that acts on an object when it is in equilibrium?
CP PHYSICS
Equilibrium Problems
Name: ____________________________________
____ period
Solve the following problems using the parallelogram method. Draw the diagrams and then find the
resultant and equilibrant vectors. Show all work!!
1.
220 N, east and 599 N, west
2.
24.0 N, east and 18.0 N, south
3.
13.5 N, W and 32.0 N, N
4.
45.0 N, west and 27.0 N, north
5.
24.5 N, E and 72.0 N, S
CP PHYSICS
FRICTION EXAMPLE PROBLEMS
1)
Name: _____________________________
___ period
Constant Velocity
Free body force diagram:
Equations:
Example Calculations:
1.
A box weighing 43.2 N is pulled horizontally until it slides uniformly over a level floor.
If the applied force is 6.30 N, what is the coefficient of friction between the box and the
floor?
2.
If a horizontal force of 30 N is required to slide a 12 kg wooden crate across a floor at
constant velocity, what is the coefficient of sliding friction between the crate and the
floor?
3.
What applied force is required to keep a 780 N box moving at a constant velocity across
a warehouse floor if the coefficient of friction between the box and the floor is 0.21?
CP PHYSICS, FRICTION EXAMPLE PROBLEMS, page 2
2)
Acceleration
Free body force diagram:
Equations:
Example Calculations:
1.
A force of 20 N is applied to accelerate a 9.0 kg wagon at 2.0 m/s2 along the sidewalk.
How large is the force of friction?
2.
A crate with a mass of 62 kg experiences a frictional force of 530 N when it is
pushed along the sidewalk. What force must be applied to the crate to give it
an acceleration of 0.35 m/s2?
CP PHYSICS
FRICTION PROBLEMS I
Name: ___________________________________
____ period
Solve the following problems. Draw and label the free body diagrams. Use GUESS!!!!!
1.
A box weighing 155 N is pushed horizontally down the hall at constant velocity. The applied
force is 83 N, what is the coefficient of friction between the box and the floor?
2.
What force must be applied to a 625 N laboratory cart to keeping it moving with a constant
velocity down a school hallway if the coefficient of friction between the cart and the floor is
0.38?
3.
A 4.7 kg ball is sent rolling with uniform motion across a meter stick track with a horizontal
force of 19.2 N. What is the coefficient of sliding friction between the ball and the meter sticks?
4.
A 57 kg box of anatomy supplies is pushed down C hall. The force of friction acting on it is
11.3 N. If the teacher makes the box accelerate down the hallway at 0.42 m/s 2, what force did
she apply to it?
5.
A 116 N force is applied to 25 kg baby carriage to make it accelerate down the sidewalk at
3.6 m/s. What is the force of friction acting on the carriage?
6.
What is the acceleration of a 0.63 kg toy car on a sidewalk if a force of 5.8 N is applied to it to
overcome 4.2 N of friction?
CP PHYSICS
Name: _______________________________
VERTICAL MOTION EXAMPLE PROBLEMS
___ period
Free body force diagram:
Equations:
Example Calculations:
1.
A small weather rocket weighs 12.6 N. Its engine fires and exerts an upward force of
15.4 N. What is the acceleration of the rocket?
2.
In bench pressing a 100 kg barbell, a weight lifter applies a force of 1040 N. How large
is the upward acceleration of the barbell during the
lift?
CP PHYSICS
VERTICAL MOTION PROBLEMS
Name: ______________________________
____ period
Solve the following problems. Draw and label the free body diagrams. Use GUESS!!!
1.
A 3.6 kg ball is launched into the air with a force of 74 N. What is its upward
acceleration?
2.
A 275 N rocket is launched straight upwards with a force of 419 N. What is its
acceleration?
3.
A weather balloon with a mass of 1.8 kg is launched upward with a force of 15 N. What
is its acceleration? Based on your answer, what is happening to the balloon once it is
released?