Transcript PowerTemplate - Stafford Intermediate School

Week
Objective
Student will:

Study the effects of forces on objects
though
 Newton’s First Law of Motion
 Law of Inertia
 Newton’s Second Law
 Newton’s Third Law
Cornell Notes (1/3)
Questions
1) What is Newton’s
First Law Of
Motion?
Newton’s First Law of Motion


Law of Inertia
 Inertia means “Tendency to resist
change in motion”
An object at rest, stays at rest.
Object in motion, stays in motion
unless acted upon by a force.
Cornell Notes (2/3)
2) How do you know
if an object is
moving or not?
Net Force (Resultant force): Sum up all
the forces
CPO Lab #0
Part II: Analyzing The Event
CPO Lab #0
Part II: Analyzing The Event
Cornell Notes (1/3)
Questions
1) Newton’s 2nd Law
is summarize with
what formula?
Newton’s 2nd Law:
𝐹𝑛𝑒𝑡 = 𝑚𝑎
Net Force = Mass x Acceleration
Force is measured in Newton (N)
Mass is measured in kilograms (kg)
Acceleration is measured in (m/s2)
Cornell Notes (2/3)
2) How does friction
help move you
forward when
walking?
3) A bat hits a ball
with a force of 50
N, what is the force
of the ball on the
bat?
Newton’s 3rd Law: For every action
force, there is a reaction force of equal
magnitude (size), yet opposite in
direction.
Forces ALWAYS come in pairs
 Bat hits ball/ball hits bat
 Push on wall/wall pushes back
 Falling object pulled by Earth/Earth
pulled by falling object
Cornell Notes (3/3)
Example
4) Is it possible to
push someone
harder than they
push you?
A 20 Kg girl and a 40 Kg boy are on ice. The girl
pushes a boy with a force of 20 N. What force must
the girl experience?
Cornell Notes (1/5)
Example: Newton’s Second Law
The Human Torch is pulling the Thing (not an easy feat) straight
up off the ground by applying a force of 3000 N. What is the
magnitude of the Thing’s acceleration? Assume The Thing’s
mass is 224 kg.
Cornell Notes (2/5)
Steps
1) Define
Think of ALL the
forces that act upon
an object
Given:
m = 224 kg
Fnet = 3000 N
g = 9.8 m/s2
Unknown:
𝑎=?
The Human Torch is pulling the Thing (not an easy feat)
straight up off the ground by applying a force of 3000 N.
What is the magnitude of the Thing’s acceleration?
Assume The Thing’s mass is 224 kg.
Cornell Notes (3/5)
2) Plan
Choose an equation or situation:
𝐹𝑛𝑒𝑡 = 𝑚𝑎
𝐹𝑔 = 𝑚𝑔
Rearrange the equation to isolate the
unknown:
𝐹𝑛𝑒𝑡 = 𝑚𝑎
𝐹𝑎𝑝𝑝 + −𝐹𝑔
=𝑎
𝑚
𝐹𝑛𝑒𝑡 𝑚𝑎
=
𝑚
𝑚
𝐹𝑎𝑝𝑝 + −𝑚𝑔
=𝑎
𝑚
𝐹𝑛𝑒𝑡
=𝑎
𝑚
𝐹𝑎𝑝𝑝 − 𝑚𝑔
=𝑎
𝑚
Cornell Notes (4/5)
3) Calculate
Substitute the values into the equation and
solve
𝐹𝑎𝑝𝑝 − 𝑚𝑔
=𝑎
𝑚
3000 − 224 ∙ 9.8
=𝑎
224
804.8
=𝑎
224
𝑎 = 3.592857143
𝑎 = 3.593 𝑚/𝑠 2
Cornell Notes (5/5)
4) Evaluate
The Thing is accelerating
3.593 m/s2 upward.
Cornell Notes (1/5)
Example: Newton Second Law
In order to travel, the Hulk has to leap from one
place to another. Assuming his mass is 521.63
kg (1150 lbs), calculate the force that he exerts
on the ground when he accelerates from 0 m/s to
391m/s (874.642 mph) in 0.8 seconds.
Cornell Notes (2/5)
Steps
1) Define
Force needs
magnitude and
direction
Given:
m = 521.63 kg
𝑣𝑖 = 0 m/s
𝑣𝑓 = 391 m/s
t = 0.8 seconds
Unknown:
F=?
In order to travel, the Hulk has to leap from one place to
another. Assuming his mass is 521.63 kg (1150 lbs),
calculate the force that he exerts on the ground when he
accelerates from 0 m/s to 391m/s (874.642 mph) in 0.8
seconds.
Cornell Notes (3/5)
2) Plan
Choose an equation or situation:
aavg
vf − vi
=
∆t
F = ma
Rearrange the equation to isolate the
unknown:
aavg
vf − v i
=
∆t
F = ma
Cornell Notes (4/5)
3) Calculate
Substitute the values into the equation and
solve
vf − vi
aavg =
∆t
391 − 0
aavg =
0.8
aavg = 488.75 m/s 2
F = ma
F = 521.63 ∙ 488.75
F = 254946.6625
F = 254946.663 N
Cornell Notes (5/5)
4) Evaluate
The Force is positive, indicating an
upward direction, and is a very large
number (after all, it is the Hulk).
Through Newton’s Third Law of
motion, the Hulk will need to exert
a force of 291429.46 N to
accelerate himself.