1. Science Chapter 5 Section 2
Machines
Science Chapter 5 Section 2

2. Machine Definition: A device that makes work easier
Does NOT decrease work!
Makes work easier by:
Changing direction of force needed to do work
Changing distance force is applied (also changes amount of force)

3. Change direction of Force

4. Change distance force is applied

5. Machine Two forces are involved in using machine:
Effort force (FE): the force applied to the machine
Resistance force (FR): the force the machine uses on the object we want to move
FR is also sometimes called load force

7. Machine Two kinds of work calculated when using the machine:
Input Work: Work done by you to use the machine (Win)
Output Work: Work done by the machine to move the object (Wout)

8. Remember! Work is done by transferring energy!
We cannot create or destroy energy!
Some energy becomes non-useful any time work is done!
Therefore, Wout is always less than Win!

9. Mechanical Advantage MA: the amount a machine helps you do the work
Calculated in two ways:
Ideal Mechanical Advantage
Actual Mechanical Advantage

10. Ideal Mechanical Advantage
IMA = deffort / dresistance
This is theoretical MA
Does not take “loss” of energy into account

11. Actual Mechanical Advantage
AMA = Fresistance / Feffort
“Real World” mechanical advantage
Takes friction and “loss” of energy into account

12. Example
Grok uses a ramp to push a 1500 N rock up to his cave from the valley below. The vertical distance from the valley floor to the cave is 50 m. The ramp is 150 m long, and Grok must push with a force of 500 N to move the rock up the ramp. What is the IMA of the ramp?

13. Grok’s Rock Example Continued
What we know:
Feffort=500 N
Fresistance=1500 N
deffort=150 m
dresistance=50 m
Equation
IMA = deffort / dresistance

14. Grok’s Rock Example Substitute numbers in: Solve: Check for units!
IMA = 150m/50m
Solve:
IMA = 3
Check for units!
Whoops, no units for MA!

15. Efficiency!
Efficiency is another measure of how well the machine works
Efficiency compares the work you get out to the work you put in
Efficiency = Wout/Win x 100 (given as percent)
Efficiency is ALWAYS less than 100%!