(Chapter 5 Section 2)

Does using machines mean you do less work? NO!  In fact, you usually do more work. So why do we use them? What are they?

 

Machine: a device that makes doing work easier.  They can:

·      Increase force, like a car jack

o    Can you lift a car?  No!  A jack multiplies your force.

·      Increase distance, like a ramp

·      Can you lift a sofa into a truck?  No!  A ramp allows you to apply less force over a greater distance. 

·      Change direction of force, like an ax

·      Can you pry apart a log?  No!  An ax changes your downward force into sideways force.  Also, the jack changes a downward force into an upward force. 

 

2 Forces are found in machines

·      F_e = Effort Force = the force you put into the machine

·      F_r = Resistance Force = force the machine applies to object

2 Kinds of Work are found in machines

·      W_in = the amount of work you put in to a machine

·      W_out = the amount of work the machine does

Efficiency of a machine:

·       For an ideal machine, efficiency = 1.  Efficiency is never > 1. 

Mechanical Advantage: describes multiplication of force

·       MA = F_r/F_e  (Usually MA>1, MA= 1 if changing direction of force)