Are machines really more efficient than people?
Lets have a quick review of simple machines.
- machine is a device
that does work
- machines make work easier - they change the force or distance or change the direction of the force
- few or no moving parts
- use energy to work
You are doing work when you use a force to cause motion.  A force is a push or pull, and when applied to a machine is called effort force or work input. Machines exert force over a distance and this is called output force. The work the machine is doing is called the work output. You are doing work when you use a force to cause motion. Work equals force times distance.  w = F x d
Did you know that 2 or more simple machines working together form a compound or a complex machine. 
This wheelbarrow is a compound machine made up of 2 simple machines. The 2 simple machines are lever and wheel and axle.
wheel and axle
All kinds of machines make work easier for us by changing the direction or size of the applied force. The amount of force we save by using the machine is called mechanical advantage.
This bicycle I have here, I wonder if it is an efficient machine?  I was thinking of taking up racing, you know, like the Tour de France. Would it be an efficient machine for me?  My friend just wants a bike for riding around. I wonder if it would be efficient for him. I guess this bicycle would be efficient for him if it was easy to use for the everyday rider, easy on the maintenance and easy to keep clean.
Question??  What makes a mountain bike "good" ?
Introduction to Simple Machines
       - an excellent site
Simple Machines, Work, Force, Energy
                   very good! 
Investigate and Report on Simple Machine
                      - excellent
Amusement Park Physics - GREAT!
How Stuff Works - type in the machine
                            and then check it out
TEACHERS Marvelous Machines
Wheel & Axle
- with permission from Utah State Office of Education
Science Homepage
Teacher Resources
HOME - bj's MST
Edheads presents Simple Machines
EXCELLENT - cartoon style, audio, interactive,  flash player, also has compound machines
( highlight to see answers ).
The Bicycle As A System
"To explore the nature of systems by examining the systems that make a bicycle work" - lesson
Let's check out the science of cycling!

In the sport of cycling, the wheels of the bicycle vary for different types of ground. When first invented, bicycles had a large front wheel therefore a large radius as well. This made them extremely efficient and fast to ride on flat surfaces but they were very dangerous to the rider. The centre of mass was high and the bike would flip quite easily.
  With the invent of pneumatic tires (tires filled with air)  the ride became a great deal safer and more comfortable. Now, off road bikes have wide tires and racing bikes have very narrow tires. The very thin tires work well because they minimize friction and cut back the weight of the wheel. It might seem reasonable that these tires would also work well on rough terrain, but the physics says differently. The fat tires are wide enough to actually float above many of the dips and troughs (roughness) in the ground. They attach only to the high spots whereas a thin tire would sink into the valleys and increase contact and friction.
Cyclist in competition, try to minimize friction by wearing a specially designed helmet that allows air to flow over their heads and down their backs. An ordinary helmet would cause turbulent wind flow at the neck. This causes drag. Competitors also wear clothing to decrease drag. Some cyclists will generate 300 - 500 W (watts) of power to maintain speeds of 45-56 km / hour.

The following links will take you to futher information about either the
Bicycle As A System or The Science of Cycling.

Science of Cycling
Aerodynamics of Bicycles

Wind Tunnel Tuneup
Forces and Things
Tour de France
Lots more links on
Mechanical Efficiency
and  Advantage