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 = Ffd

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.