1. Simple Machines

2. Example A frictionless 30 o 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?

3. 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

4. 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) KE 1 + PE 1 = KE 2 + PE 2 + Dissipated Work

5. Friction Most Common Friction depends on the distance traveled W f = F f d KE 1 + PE 1 = KE 2 + PE 2 + F f d

6. 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.