Physics Advanced I
Forces and the Laws of Motion
Chapter 4
Key Terms
Force
Weight (gravitational force)
Inertia
Normal Force
Net Force
Friction
Equilibrium
Four Fundamental Forces
Air Resistance
Static vs. Kinetic Friction
Newton’s First Law (law of
inertia)
Newton’s Second Law
(Fnet = ma)
Newtons’s Third Law
(Action-reaction pairs)
Coefficient of Friction
Contact vs. Field Forces
Essential Question
How are forces and Newton’s Laws of motion used to describe motion?
Unit Learning Targets (I can…
Section 1
1. Explain the characteristics of force
2. Identify the basic forces (Weight, normal force and friction, spring force, tension,
air resistance, applied force)
3. Draw free-body diagrams showing forces acting on an object
4. Explain the cause of acceleration of any object.
5. Explain the difference between accelerated and non-accelerated motion as it
relates to equilibrium.
Section 2
1. Explain the characteristics inertia.
2. Explain net force, and the difference between balanced force and unbalanced
force. Explain how Aristotle and Galileo/Newton differed in their explanations of
why objects stay moving and why objects stop moving.
3. Interpret the role of inertia in the motion of objects as it relates to Newton’s 1st
law of motion
4. Explain how it is possible for an object that is in equilibrium to be in motion.
5. Solve net force problems using vectors
Section 3
1. Apply the relationships between net force, mass and acceleration as stated in
Newton’s 2nd law of motion to objects of differing masses and accelerating net
forces.
2. Solve motion problems using Newton's second law of motion.
3. Consider two objects, one with 1 kg of mass and the other with 10 kg of mass.
Use Netwon’s 2nd law of motion to explain why these two objects, neglecting air
resistance, fall at the same rate of acceleration.
4. Explain the fundamentals of Newton’s 3rd law of motion
5. Analyze force pairs for any interaction
Section 4
1. Explain the difference between mass and weight, and how weight is related to
gravitational force.
2. Solve conversion problems for mass and weight.
3. Explain the fundamentals of gravity
4. Explain the fundamentals of normal force
5. Explain the fundamentals of friction.
6. Explain the difference between static and kinetic friction.
7. Solve problems using the friction equations
8. Explain what causes air resistance to increase or decrease
9. Explain how air resistance causes different objects to fall in different manners.
10. Explain how it is possible for a falling object to stop accelerating without coming
to rest.
11. Explain the characteristics of the four fundamental forces
Section 1
1. Explain the characteristics of force
2 Identify the basic forces (Weight, normal force and friction, spring force, tension,
air resistance, applied force)
3. Draw free-body diagrams showing forces acting on an object
4. Explain the cause of acceleration of any object.
Acceleration is caused by unbalanced force acting on the object, resulting in a net force
greater than zero.
5. Explain the difference between accelerated and non-accelerated motion as it
relates to equilibrium.
Accelerated motion is recognized by a change in motion (change in velocity, change in
speed, change in direction). Non-accelerated motion is evidenced by objects at rest or at
a constant velocity (same speed, same direction)
Section 2
6. Explain the characteristics inertia.
7. Explain net force, and the difference between balanced force and unbalanced
force. Explain how Aristotle and Galileo/Newton differed in their explanations of
why objects stay moving and why objects stop moving.
8. Interpret the role of inertia in the motion of objects as it relates to Newton’s 1st
law of motion
Inertia is the tendency of any object to resist any change in motion. This means that if
the object is in equilibrium (at rest or constant velocity), it will require an unbalanced
force to change its motion. In other words, once set in motion, an object does not seek to
change its motion, and will continue in equilibrium unless a change is caused.
9. Explain how it is possible for an object that is in equilibrium to be in motion.
The condition of equilibrium is produced by balanced forces or by no forces (not really
possible). This occurs at constant velocity, where forces interact and ultimately cancel
out, producing a net force equal to zero. Example, falling object reaching terminal
velocity where weight is balanced by air resistance.
10. Solve net force problems using vectors
Section 3
6. Apply the relationships between net force, mass and acceleration as stated in
Newton’s 2nd law of motion to objects of differing masses and accelerating net
forces.
Keeping net force constant, an increase in mass produces a decrease in acceleration
(inverse relationship)
Keeping mass constant, an increase in the net force (accelerating force) produces a
corresponding increase in acceleration (direct relationship)
7. Solve motion problems using Newton's second law of motion.
8. Consider two objects, one with 1 kg of mass and the other with 10 kg of mass.
Use Netwon’s 2nd law of motion to explain why these two objects, neglecting air
resistance, fall at the same rate of acceleration.
9. Explain the fundamentals of Newton’s 3rd law of motion
Forces act in pairs. The action force is equal to and opposite of the reaction force. This
means that two different objects when interacting will each experience the same impact
force.
10. Analyze force pairs for any interaction
Section 4
3
Explain the difference between mass and weight, and how weight is related to
gravitational force.
Mass is the measure of the amount of matter that composes an object.
Weight is a measure of the force of gravity acting on a mass, and is determined by
multiplying mass time rate of acceleration due to gravity.
4
5
6
7
Solve conversion problems for mass and weight.
Explain the fundamentals of gravity
Explain the fundamentals of normal force
Explain the fundamentals of friction.
Friction is an oppositional force that occurs when two object in contact are either
attempted to be pushed past (static friction) or actually sliding past each other (kinetic
friction). It increases with surface roughness, and depends upon the compositon of the
materials in contact.
8
Explain the difference between static and kinetic friction. (see previous)
Static is friction at rest and kinetic is friction in motion. Static is greater than kinetic.
9
Solve problems using the friction equations.
Coeff. Of friction = Fk/Fn
or Fs,max/Fn
10 Explain what causes air resistance to increase or decrease
Increases: greater/lesser exposed surface area, greater/lesser speed through the air,
greater or lesser density of air
11 Explain how air resistance causes different objects to fall in different manners.
12 Explain how it is possible for a falling object to stop accelerating without coming
to rest.
As an object falls, its speed increases. This gradually increases the air resistance, which
begins to balance the difference between the object’s weight and the drag it experiences.
When air resistance balances weight, the object is in equilibrium as it is falling, and
ceases to accelerate, traveling at a maximum constant speed, known as terminal velocity.
13 Explain the characteristics of the four fundamental forces
Chapter 4
Problems to Solve
Problem A
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Textbook
Problem Bank, Problem A
Workbook, Problem A
Problem B
a)
Free-Body Diagrams
pg. 124 (#1-2), pg. 143 (#1), pg 145 (#7-9)
(#1-3)
(#1-3)
Determining Net Force
Forces acting in one dimension or along x and y directions,
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b)
Textbook
Workbook
Problem Bank, Problem B
Standardized Test Prep
Pg. 145 #10, #11
Pg. 34 (#1,2)
(#4, 7)
Pg. 150 (#3)
Two forces acting at right angles, the resultant or equilibrant
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Textbook
Workbook
Problem Bank, Problem B
pg. 128 (#2, #3); pg 129, (#3);
pg. 34 (#3)
(#5)
c)
Resolving for Fx and Fy, and using Pythagorean Theorem and inverse tan to find
net force
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d)
Finding resultant or net force of two or more forces acting at angles
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e)
Problem Bank, Problem B (#1, 2)
Finding Tension in two support ropes or cables at equal but opposite angles
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f)
Textbook pg. 128, #1; pg 145 #12
Problem Bank, Problem B (#3, 6)
SAT Mathematics (#1, #2)
Example problems in class, on line HW 15
Workbook pg 34 (#4)
Finding net force acting on object that is on an incline
Textbook pg 147 #40, 41
Problem C
a.
Newton’s Second Law of Motion
Fnet = ma
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Textbook pg. 132 (#1-4), pg. 134 (#1), pg. 146 (#19, 20, 21) pg 148 (#45a)
Problem Bank (#7)
SAT Bellringer (#3, #4, #5)
b.
Finding acceleration and/or net force or mass given other information (time,
velocity, horizontal or vertical displacement)
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Textbook pg 132 (#5), pg 134 (#4); pg 146 (#22); pg 148 #43,
Workbook pg. 35 (#1, 2, 3, 4, 5)
Problem Bank (1, 2, 4, 5)
SAT Bellringer (#6, 7)
Standarized Test Prep (#5)