# PHYS 101 Lecture 4: Week 4

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4 Feb 2017
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PHYS 101 LECTURE NOTES WEEK 4
Spencer Kociba
Drexel University
Lecture 7 (01/31/2017)
Apparent weight (normal force that acts on you to counteract other forces)
 
In an elevator, accelerating upwards results in a larger apparent weight
(normal force is larger) and accelerating downwards results in a smaller
apparent weight (normal force is smaller)
In free fall, 
Lecture 8 (02/02/2017)
Frictional forces
When a body rests or slides on a surface the friction force acts parallel to the
surface
Kinetic friction acts when a body slides over a surface
n=normal force
=coefficient of kinetic friction
Occurs because of the interactions between molecules as the object is
moving
Static friction acts when there is no relative motion between bodies
 
n=normal force
= coefficient of static friction
Need to overcome inertia
Opposes the object’s tendency to move (ex. Ffriction is up a ramp
because an object wants to move down the ramp)
Before an object slides, static friction acts. Once it starts moving, kinetic
friction acts
Object at rest ( used) when there is not a large enough force to overcome
friction
At rest,
Object in constant motion (used)
Fn
Ft
Ffs
F
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