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Mechanical Advantage and Simple Machines
Work Input and Output
• A machine is anything that transforms energy– Work Input: the work/energy supplied to the
machine– Work Output: the work/energy that comes
out of the machine
Law of Conservation of Energy
Energy cannot be created or destroyed, just transformed from one form into another.
Work Input and Output
• The energy output of a process or machine can never exceed the energy input.
• Work In ≥ Work Out
• Some energy may be “lost” to friction
• This energy is released as heat, sound, etc.
Mechanical Advantage
• The ratio of output force to input force– Input Force: The force you apply to the
machine– Output Force: The force the machine applies
to the object you are trying to move
Mechanical Advantage
MA > 1: The output force is greater than input
MA < 1: The output force is less than input
Mechanical Advantage
1. A machine uses an input force of 200. newtons to produce an output force of 800. newtons. What is the mechanical advantage of this machine?
2. Another machine uses an input force of 200. newtons to produce an output force of 80.0 newtons. What is the mechanical advantage of this machine?
Mechanical Advantage3. A machine is required to produce an output force
of 600 newtons. If the machine has a mechanical advantage of 6, what input force must be applied to the machine?
4. A machine with a mechanical advantage of 10. is used to produce an output force of 250 newtons. What input force is applied to this machine?
5. A machine with a mechanical advantage of 2.5 requires an input force of 120 newtons. What output force is produced by this machine?
Mechanical Advantage
6. 200. Joules of work is put into a machine over a distance of 20. meters. The machine does 150. Joules of work as it lifts a load 10. meters high. What is the mechanical advantage of the machine?
Efficiency
• The ratio of output work (or energy) to input work (or energy)– Similar to mechanical advantage, but with
work instead of force– Expressed as a percent or decimal
• Efficiency = work output / work input
Efficiency
• A car’s efficiency is only 13 percent. If the input work for the car is 200. joules, what is the output work?
• A simple machine produces 25 joules of output work for every 50 joules of input work. What is the efficiency of this machine?
Simple Machine
• An unpowered mechanical device that accomplishes a task with only one movement
• Simple machines are used to change the amount of force applied to an object
• HOW DO THEY DO THIS??????
Simple Machine
• Work in = Work out
W = FdWhen work is done over a…
• larger distance, there is a smaller force.
• smaller distance, there is a larger force.
The Lever
The Levera rigid bar that is free to turn about a
fixed point called the fulcrum
Every Lever has three (3) parts: 1. Input Arm (aka Effort Force) - The work
done on the Lever.
2. Fulcrum – A fixed pivot point.
3. Output Arm (aka Resistance Force or Load) - What you are trying to move or lift.
The Lever
The Lever
• There are 3 classes of levers, distinguished by the location of the fulcrum with respect to the input and output forces.
1st Class Lever
1st Class Lever
• The Fulcrum (fixed pivot point) is located between the Effort (Input) and the Resistance (Output) Forces.
• The effort and the resistance move in opposite directions.
• The effort force pushes down in order to lift the resistance or load.
1st Class Lever
• When the fulcrum is closer to the effort than to the load (input arm < output arm):– Output force is less than input– Output speed/distance is more than input
1st Class Lever
• When the fulcrum is closer to the load than to the effort (input arm > output arm):– Output force is greater than input– Output speed/distance is less than input
1st Class Lever
• When the fulcrum is midway between the effort and the load (input arm = output arm):– Input and output force, speed, and distance are
equal
1st Class Lever
• Examples:– Seesaw– Crowbar– Scissors– https://
www.youtube.com/watch?v=SLBdnpoKa3Y
• Mechanical Advantage can be less than, greater than, or equal to 1 depending on the ratio of the input and output arm length
2nd Class Levers
2nd Class Lever
• The load is between the effort and the fulcrum.
• The fulcrum is at one end of the lever.
• The fulcrum is usually closer to the load.– Input arm is longer than output arm.
• Output force is greater than input force.
2nd Class Levers
• Examples:– Wheelbarrow– Bottle opener– Citrus juicers
• Mechanical Advantage is greater than 1 since input arm is longer than output arm, so input force is less than output force
3rd Class Levers
3rd Class Levers
• The effort is between the load and the fulcrum.
• Output force is less than input force,
• Output speed/distance is greater than input speed/distance
3rd Class Levers
• Examples:– Broom– Shovel– Fishing rod
• Mechanical Advantage is less than 1 since input arm is shorter than output arm, so input force is greater than output force
Types of Levers
Levers & Mechanical Advantage
1. A lever used to lift a heavy box has an input arm of 4 meters and an output arm of 0.8 meters. What is the mechanical advantage of the lever?
2. What is the mechanical advantage of a lever that has an input arm of 3.0 meters and an output arm of 2.0 meters?
The Inclined Plane(aka The Ramp)
The Inclined Planea sloping surface that does not move
• An inclined plane provides for less effort, NOT less work.
• The trade off is greater distance to travel.
The Inclined Plane
• Used to reduce the force needed to overcome the force of gravity when lifting or lowering a heavy object.
The Inclined Plane
Ramps & Mechanical Advantage
1. A 5.0-meter ramp lifts objects to a height of 0.75 meters. What is the mechanical advantage of the ramp?
2. A 10.-meter long ramp has a mechanical advantage of 5.0. What is the height of the ramp?
3. A ramp with a mechanical advantage of 8.0 lifts objects to a height of 1.5 meters. How long is the ramp?
