# PHY 101 Study Guide - Comprehensive Final Guide: Inelastic Collision, Elastic Collision, Momentum

by OC1314461

This

**preview**shows pages 1-3. to view the full**42 pages of the document.**UM

PHY 101

FINAL EXAM

STUDY GUIDE

Only pages 1-3 are available for preview. Some parts have been intentionally blurred.

Only pages 1-3 are available for preview. Some parts have been intentionally blurred.

Chapter 6

● 6-1 Frictional Forces

● friction: the force required to overcome the resistance of microscopic hills and

valleys and bumping together

● even smooth surfaces are jagged at the atomic level which causes resistance to

an objects motion; the resistance is the force of friction

● friction is thought of as something that should be reduced or eliminated if

possible

● friction is helpful in some situations (starting to walk, turning the corner while

driving)

● Kinetic Friction

○Kinetic friction- the friction encountered when surfaces slide against one

another with a finite relative speed

○fk acts to oppose the sliding motion at the point of contact between the

surfaces

○When the normal force (N) is doubled fk is also doubled; fk is proportional

to the magnitude of N.

○fk= kN

■ k is referred to as the coefficient of kinetic friction, it is the

constant of proportionality

○N in special cases equals the weight of the object overcoming friction but if

someone pushes down on the object N becomes greater than the

objects weight which would increase friction

○N is less than the weight of the object if it is on an incline

○The force of friction opposes motion and is thus not a vector equation b/c N

is perpendicular to the direction of motion

○When an object is pulled at speed v and then later 2v, the force of kinetic

friction is about the same in each case; it does not double fk is

independent of the relative speed of surfaces

○If the area of contact of an object is reduced, the force of friction remains

the same regardless of the area of contact; fk is independent of the

area of contact b/t the surfaces

● Static Friction

○Static friction- the friction that keeps two surfaces from moving relative to

one another due to the microscopic irregularities of surfaces that are in

contact

○Typically stronger than kinetic friction b/c the hills and valleys of each

surface can nestle into one another

○When an object is motionless, the fs is zero

○When a force f1 attempts to pull an object and it does not move, f1=fs; if f1

increases and the object still does not move, fs has also increased to the

same value

○When the object starts moving, f s is overcome and fk takes over; the upper

limit that fs reaches is called fs,max > fs > 0

○fs,max= sN

■ s is the coefficient of static friction, the constant of

proportionality; it is usually greater thank k showing that fs > fk

○fs is independent of the area of contact between the two surfaces

find more resources at oneclass.com

find more resources at oneclass.com

###### You're Reading a Preview

Unlock to view full version

Only pages 1-3 are available for preview. Some parts have been intentionally blurred.

○fs is parallel to the surface of contact and opposite the direction of

motion

● If a car skids, the friction acting on it is kinetic, if it breaks and its wheels are

still rolling the friction is static and can be stopped in less a distance than if its

wheels are locked up

● 6-2 Strings and Springs

● Strings and Tensions

○Tension- the force in a spring that causes it to become taut; the force

pulling the ends of a string apart; at any given point tension pulls equally

to the right and left

○For the problem of a rope that holds a box from the ceiling

■ the rope holds the box at rest so the tension where the rope

attaches to the box is the weight of the box

■ at the midpoint of the rope the tension is the weight of the box +

half the weight of the rope

■ at the ceiling the tension is the weight of the box and the rope

○pulleys are used to redirect a force exerted in a strong, and an ideal pulley

has no mass or friction in its bearings; it changes the direction of the

tension in a strong without change its magnitude

○multiple pulleys can magnify a force

● Spring’s and Hooke’s Law

○If you stretch or compress a string of length L by L + x; the spring

pushes/pulls back by a force F; if x is increased to 2x the force becomes

2F

○A spring exerts a force that is proportional to the amount, x, by which it is

stretched or compressed

F= kx (magnitude only) F= -kx (magnitude and direction)

○k- spring force constant; the constant of proportionality; has units of N/m

○if the spring is stretched, the magnitude of kx is in the negative x

direction

○if the spring is compressed, the value of x is negative and the magnitude of

kx is also negative

○if a spring is stretched too far from equilibrium it will permanently deform

○ideal springs- springs that are massless, and are assumed to obey hooke’s

law

○the forces that hold atoms together are modeled by hooke’s law

● 6-3 Translational Equilibrium

● translational equilibrium- the net force acting on an object is zero; the sum

of the forces = 0

● when the system is in two dimensions the sum of forces in both the x and y

direction must be at zero

● Translational Equilibrium in Tension

○if the acceleration of the system is zero, the upward tension in the rope is

equal to the weight of the mass hanging from the rope (mg); this is also

the force the person must exert downward on the rope to pull it; same as

tension downward

○The tension in the chain holding the pulley tension up – tension down from

the weight – tension down from the person pulling; thus the tension in

the change is twice the downward tension or 2mg

find more resources at oneclass.com

find more resources at oneclass.com

###### You're Reading a Preview

Unlock to view full version