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DEVIL PHYSICS THE BADDEST CLASS ON CAMPUS IB PHYSICS PRE-IB PHYSICS
DEVIL PHYSICSTHE BADDEST CLASS ON
CAMPUSIB PHYSICS
PRE-IB PHYSICS
TSOKOS LESSON 2-5NEWTON’S SECOND AND THIRD LAWS
Reading Activity Questions?
Assessment Statements
2.2.8. State Newton’s second law of motion.
2.2.9. Solve problems involving Newton’s second law.
2.2.14. State Newton’s third law of motion.
2.2.15. Discuss examples of Newton’s third law.
Objectives Recognize situations of equilibrium, i.e.
situations where the net force and hence the acceleration are zero.
Draw the forces on the body of interest and apply Newton’s second law on that body, .
Recognize that the net force on a body is in the same direction as the acceleration of that body.
Identify pairs of forces that come from Newton’s Third Law.
Video: Newton’s Second Law of Motion
Newton’s Second Law
The net force on a body is proportional to that body’s acceleration and is in the same direction as the acceleration
where m is mass, the constant of proportionality
amF
Newton’s Second Law
The unit of force is the Newton (N) 1N = 1kg•m/s2 ma = (kg)(m/s2)
Weight is a force caused by gravitational attraction
amF
gamgamF
Newton’s Second Law
When you jump from the emergency exit after the fire alarm gets hit by a volleyball, how do you minimize the force on your body?
amF
Newton’s Second Law
When you jump from the emergency exit after the fire alarm gets hit by a volleyball, how do you minimize the force on your body?
You bend your knees to decrease the acceleration and execute a parachute landing fall to translate vertical acceleration into rotational acceleration.
amF
Newton’s Second Law
How do car manufacturers try to minimize the forces absorbed by passengers during a collision?
amF
Newton’s Second Law
How do car manufacturers try to minimize the forces absorbed by passengers during a collision?
Air bags and crumple zones.
amF
Newton’s Second LawSample Problem A 200-kg hot air
balloon is held to the ground by two wires that make a 60-degree angle to the ground. When the wires are released, the balloon accelerates upward at 3 m/s2. What is the tension in each cable?
amF
Newton’s Second LawSample Problem A 200-kg hot air
balloon is held to the ground by two wires that make a 60-degree angle to the ground. When the wires are released, the balloon accelerates upward at 3 m/s2. What is the tension in each cable?
amF
FL
FgFTy
Newton’s Second LawSample Problem A 200-kg hot air
balloon is held to the ground by two wires that make a 60-degree angle to the ground. When the wires are released, the balloon accelerates upward at 3 m/s2. What is the tension in each cable?
mgmaF
maFFamF
mgF
FFF
FFFamF
L
gL
g
gLTy
TygL
0
Newton’s Second LawSample Problem A 200-kg hot air
balloon is held to the ground by two wires that make a 60-degree angle to the ground. When the wires are released, the balloon accelerates upward at 3 m/s2. What is the tension in each cable?
NmaF
mgmgmaFmgmaF
mgF
FFF
Ty
Ty
L
g
gLTy
600
Newton’s Second LawSample Problem A 200-kg hot air
balloon is held to the ground by two wires that make a 60-degree angle to the ground. When the wires are released, the balloon accelerates upward at 3 m/s2. What is the tension in each cable?
NFSinNF
FF
Sin
NF
T
T
T
Ty
Ty
346602
6002
60
600
Terminal Velocity
When a body moves through a fluid (gas or liquid) it experiences an opposing force, similar to friction, called drag
This force is dependent on velocity For lower velocities, drag is proportional
to velocity For high velocities, drag is proportional
to velocity squared
Terminal Velocity In horizontal
movement through a fluid, when drag equals the propulsion force, velocity is constant.
In a falling body, terminal velocity occurs when the force of aerodynamic drag equals the force of gravity. k
mgv
kvmg
vFFkvF
mgF
T
T
TDg
D
g
@
Inclined Plane Problem
A 150kg mass is placed on an plane inclined at a 17° angle. The coefficient of static friction is 0.30 and the coefficient of dynamic friction is 0.25. What happens?
Fuzzy Dice Problem
A pair of fuzzy dice hang from the rearview mirror of a car. The car accelerates from a stoplight at 2m/s2. What happens?
Video: Newton’s Third Law of Motion
Newton’s Third Law of Motion If Body A exerts a force F on Body B,
then Body B exerts an equal but opposite force F on Body A.
Newton’s Third Law of MotionExamples Pushing against a wall while wearing
rollerskates. Stepping off a boat onto a dock. A helicopter hovering. A book sitting on a table.
Summary Review Can you recognize situations of
equilibrium, i.e. situations where the net force and hence the acceleration are zero?
Can you draw the forces on the body of interest and apply Newton’s second law on that body?
Can you recognize that the net force on a body is in the same direction as the acceleration of that body?
Can you identify pairs of forces that come from Newton’s Third Law?
Assessment Statements
2.2.8. State Newton’s second law of motion.
2.2.9. Solve problems involving Newton’s second law.
2.2.14. State Newton’s third law of motion.
2.2.15. Discuss examples of Newton’s third law.
QUESTIONS?
#1-25Homework
