Download Dissipative Forces

Simple Machines
Example

A frictionless 30o ramp is used to lift a
500kg crate up a vertical distance of
1.5m. If the ramp is used is 4.0m long,
a) What force is required and how
much work is done without the ramp?
b) What force is required and how
much work is done when using the
ramp?
c) What is the advantage of the ramp?
Why use a machine?


Simple machines actually increase the
amount of work because they make the
distance traveled farther so they
experience more friction
But, since there is less force required, it
is easier to do the work
Dissipative Forces




In reality, non-conservative forces cannot be
ignored: friction really does act
Dissipative force is one that reduces the total
mechanical energy
The total energy is conserved, it is just
converted into useless forms (heat from
friction)
KE1 + PE1 = KE2 + PE2 + Dissipated Work
Friction Most Common

Friction depends on the distance
traveled
Wf = F f d

KE1 + PE1 = KE2 + PE2 + Ffd

Example

A 1000kg roller coaster car starting
from a height of 40m is found to reach
a vertical height of only 25m on the
next hill. If the total distance traveled
was 400m . Find the force of friction
acting on the car.