Transcript Final Exam Review

Final Exam Review
Newton’s Laws
Friction
& Weight
Newton’s 1st Law
• Objects in motion stay in motion and
objects at rest stay at rest unless a force
acts on it.
• (Law of Inertia)
Example
•
•
The meteor in
Armageddon would
have continued toward the Earth unless
Ben and Bruce blew it off course.
• (Applied a net force to change
•
it’s motion)
Newton’s 2nd Law
• F = ma
• Key Point: A net force will change the
velocity or direction of motion of an object.
Example
• Roberto and Laura are studying across from each
other at a wide table. Laura slides a 2.2kg book
toward Roberto. If the net force acting on the book is
1.6N, what is the book’s acceleration?
Example
• Roberto and Laura are studying across from each
other at a wide table. Laura slides a 2.2kg book
toward Roberto. If the net force acting on the book is
1.6N, what is the book’s acceleration?
• Givens
•
•
m = 2.2 kg
F = 1.6 N
Example
• Roberto and Laura are studying across from each
other at a wide table. Laura slides a 2.2kg book
toward Roberto. If the net force acting on the book is
1.6N, what is the book’s acceleration?
• Givens
•
m = 2.2 kg
•
F = 1.6 N
• F = ma → 1.6N = (2.2kg)a
•
a = 0.73 m/s2
Practice
• Pg 132- Practice C
Newton’s 3rd Law
• “Every action has an equal and opposite
reaction”
• Forces come in pairs.
Weight
• Def: Force of gravity on an object’s mass.
• If “g” changes, so does weight. You
“weigh” less on Mars, because g= 3.7 m/s2
there instead of 9.8 m/s2 like Earth.
•
BIG
SMALL
Earth
Mars
Example
• Determine the weight of a 150kg man on
the surface of the earth.
• F = ma
• F = (150kg)(9.8m/s2) = 1470N
Practice
• Determine the weight of the 150kg person
on the following planets:
• Planet
Gravity
• Mercury
3.6 m/s2
• Venus
8.6 m/s2
• Jupiter
25.9 m/s2
• Saturn
11.3 m/s2
Friction
• Def: The force that resists motion
between two objects in contact together.
• Formula: Ff = μFn
• Examples: Sliding friction (box on floor)
•
Air resistance (falling objects)
•
Water resistance (swimming)
Example
• A 24kg crate initially at rest on a horizontal floor
requires a 75N horizontal force to set it in motion.
Find the coefficient of static friction between the crate
and the floor.
Example
• A 24kg crate initially at rest on a horizontal floor
requires a 75N horizontal force to set it in motion.
Find the coefficient of static friction between the crate
and the floor.
• Givens
•
Ff = 75N
•
m = 24kg
Fn = ?
Example
• A 24kg crate initially at rest on a horizontal floor
requires a 75N horizontal force to set it in motion.
Find the coefficient of static friction between the crate
and the floor.
• Givens
•
Ff = 75N
•
m = 24kg
Fn = ?
• Fn = mg = (24kg)(9.8m/s2) = 235N
• Ff = μFn → 75N = μ(235N)
•
μ = 0.32
Practice
• Pg 139- Practice D
• Problem 2