Unit 5:
Applications of Newton’s Laws
Physics Spring 2015
Agenda 4/14/15
• Review Newton’s Law Quest
– Retake policy and assignment
• FUN Lab
– Coefficient of friction
• HW: Complete FUN Lab
Agenda 4/15/15
Quest Curve: 30pts
• Retake WS and policy
• Conclude the FUN Lab
– What did we learn?
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Lab Static Friction v. Kinetic Friction
Notes: Friction
Practice FUN equation
HW: Complete Friction Problems 1
What did we learn from FUN Lab?
• How are force of friction and normal force
related?
• Which surface had more friction?
• Which surface had a greater slope?
• What does the slope tell us about the friction of
the surface?
Coefficient of Friction
• Coefficient of friction = µ
• This is a measure of how much two objects
stick together
• A greater µ means a greater amount of friction
• Friction and normal force are related by:
F f = µ * FN
Friction
• What keeps and object still?
• What keeps an object moving?
• Is it more difficult to move an object from rest,
or keep an object moving?
• Why??
Agenda 4/16/15
Collect FUN Lab Part II
• Discuss Lab
• Notes: Kinetic v. Static Friction
• Practice: FUN equation
• HW: Complete Friction Problems 1
What happened in the lab?
• Which surface had a higher coefficient of friction?
(µ)
• Why do you think this was the case?
• Which required more force, getting the mass to
move or to keep it moving?
• Why?
Kinetic v. Static Friction
• Static Friction: the friction that exists between an object at
rest and the surface it is in contact with.
• Kinetic Friction: the friction that exists between a moving
object and the surface it is in contact with.
• The coefficient of static friction always greater than the
coefficient of kinetic friction for the same surface.
µk <µs
Agenda 4/17
• Student Surveys: Complete either on phone or
chromebook
• Review FUN homework
• Homework check: FUN
• Lab: How does surface area effect friction?
Student Surveys
• Go to d155.org/clc
• On the homepage click on the student survey
link
• Login using the instructions
• Take the survey!
Surface Area
• How does surface area affect the friction on
an object?
• How do you know? Use your data.
Agenda 4/20/15
Announcements:
• Six Flags Permission Slips
– Early or Late Bus??
– Who used cash/check
• Quick Review before HW Quiz
• HW Quiz
• Surface Area and Friction
• Review for Friction Quest Tomorrow
Surface Area
• How does surface area affect the friction on
an object?
• How do you know? Think about the lab.
Surface Area
• Friction is dependent only of the normal force
acting on an object and the coefficient of friction
(stickiness) of the surface.
• Increasing surface area spreads out the frictional
force evenly.
• Decreasing surface area puts all of the friction in
one spot.
• Either way, they amount of friction remains the
same.
Net Friction
• How much friction exists between two pieces
of paper?
• What about 10 pieces of paper? (Think about
stacking paper)
• What about 125 pieces of paper??
Phone Book Demo
• Explain why this is happening?
• Each book weighs 10N, the coefficient of static friction
is .03. What is the force of friction needed to pull the
books apart if they are stacked?
• Each page weighs .01N the coefficient of static friction
is the same, however there are 125 pages in each
book. How much force is required to pull apart the
books if all the pages are stacked together?