1. 6.2 – Using Machines

2. Objectives Explain how machines make work easier.
Calculate the mechanical advantage of a machine.
Calculate the efficiency of a machine.

3. Machine A device that makes doing work easier Machines increase
applied force
and/or change
direction of applied
force to make
work easier

4. Ramps
Increasing distance reduces the amount of force needed to do the work
Machines = work easier

5. Force & Distance The same amount of work can be done when
Applying a small force over a long distance
Or applying a large force over a shorter distance
Because work equals force times distance

6. Forces Machines help move things that resist being moved
Input force = forces applied TO machine
Output force = forces applied BY machine

7. Energy
Law of conservation of energy applies…. The amount of energy the machine transferred to the object cannot be greater than the amount of energy transferred to the machine
Some energy is changed to heat due to friction
An ideal machine with no friction would have the same input work and output work.

8. MA = output force divided by input force
Mechanical Advantage
(MA) is the number of times a machine multiplies the input force
MA = output force divided by input force

9. Ideal Mechanical Advantage
The MA of a machine without friction
Calculated by dividing the input distance by the output distance

10. Efficiency
Measure of how much of the work put into the machine is changed into useful output work by the machine

11. Lubricants can make machines more efficient by reducing friction
Efficiency = MA x 100%
The efficiency of a machine is always less than 100%
WHY? Because some energy is converted to heat due to friction
Lubricants can make machines more efficient by reducing friction

12. 6.2 Enrichment Tips
Figure 3 will have 2 graphs (or 2 shaded areas, use different colors)
Use IMA to figure out input force, take output force and divide by IMA
Example: IMA of 3, output force 30 N
Input force = 10 N

13. In-Class Assignment/Homework
6.2 Reinforcement & Enrichment WKT
ORIGINAL
EXTENSION #1
6.1c WKT -Force to Work to Power Problems
p. 881 #63-64, 69