Mechanical Advantage

You mean I don’t have to use the shovel?!

Last time we discussed the different simple machines:

Wheel & Axle

Think: Why do we use machines to doThink: Why do we use machines to do work instead of doing it ourselves?work instead of doing it ourselves?

Main Concept 5: Main Concept 5: What we really want to do is get theWhat we really want to do is get the

machine to work “efficiently”. “Efficient” machine to work “efficiently”. “Efficient” basically means to “work really well”.basically means to “work really well”.

Mechanical Advantage

• Ways of making WORK easier to accomplish (less effort):

OR

Both will get the same work done, but which one takes less effort

to accomplish the work?

Think: Does more power Think: Does more power alwaysalways mean less effort? mean less effort?

Think: In the Work & Power Lab, wereThink: In the Work & Power Lab, were the steps with more power easier the steps with more power easier

for you to do? (Less or More Effort?)for you to do? (Less or More Effort?)

Using a machine allows for moreUsing a machine allows for morepower with less effort from you!power with less effort from you!This is why we use machines.This is why we use machines.

Main Concept 6:Main Concept 6:Mechanical Advantage is all about Mechanical Advantage is all about

getting the machine to make the job as getting the machine to make the job as easy for you as possible!easy for you as possible!

The equation for M.A.

ForceInput

ForceOutput

The higher the Mechanical Advantage, the easier it is to move something.

Basic M.A.= 1 We want to make the MA number bigger!!!Means more Output from the machine, less Input force from you! = less effort!!!

The Big Point: We want machines to do The Big Point: We want machines to do as much work as possible with as little as much work as possible with as little

effort from us as we can!effort from us as we can!

Think about this: Computers continue toComputers continue toget easier and easier to use.get easier and easier to use.

Think about this: How have cell phones How have cell phones become easier to use compared to original become easier to use compared to original

phones or even early cell phones!phones or even early cell phones!

= MA

Mechanical Advantage

ForceInput

ForceOutput

Main Concept 7:Main Concept 7:

TheThe Higher thethe Mechanical Advantage,, thethe Easier it is to accomplish the work.it is to accomplish the work.

Fo

rce

Fo

rce

5 N5 N

5 N5 N= 1= 1

2 N2 N

8 N8 N= 4= 4

We want to make this number bigger = easier to do

Notice that when there is moreOutput than Input force, the

MA number increases!

What the machine doesWhat the machine does

What you do

Class Inquiry Activities

Mechanical Advantage

of Inclined Planes (Ramps) Lab

Mechanical Advantage

of Levers Lab

Fo

rce

M. A. of Levers ForceInput

ForceOutput

Work = Input Force x Input Distance Work = Output Force x Output Distance

Distance

Fo

rce

Distance

Don’t forget: Work of Input = Work of Output

In this case, with the fulcrum right in the center, the forces, distance and total input/output work are exactly the same!

Think: when force anddistance are exactly thesame; is there any M.A?

Think: If the Input and Output are exactly the same is there any point to using a machine?

So how can we increase M.A. of a lever?

Fo

rce

Fo

rce

DistanceDistance

We have to adjust how we set up the machine itself!

In this case we can move the fulcrum and change the distance of the output and input:

Notice that mathematically, even though the amounts of distance and force have changed the total work done on both sides remains the same!Notice what happens to

the force and distance ofeach side when we move

Fulcrum closer to the mass

Output: Less distance but more force! Input: More distance but less force!

Work = Output Force x Output Distance Work = Input Force x Input Distance

Class 1 Levers:

Notice that the effort Notice that the effort arms are different arms are different

lengths. lengths. Longer Input/effort Longer Input/effort

“arms “give the “arms “give the scissors more scissors more

mechanical mechanical advantage.advantage.

**In other words, it **In other words, it makes it easier to makes it easier to

cut stuff!cut stuff!

Output/Result Output/Result ArmArm

Input/Effort Input/Effort ArmArm

Output/Result Output/Result ArmArm Input/Effort Input/Effort

ArmArm

Class 2 Lever:

If we were to If we were to increase the length increase the length of the input arms on of the input arms on

the wheelbarrow, the wheelbarrow, we would give it we would give it

more mechanical more mechanical advantage.advantage.

In other words, it In other words, it makes it easier to lift makes it easier to lift

stuff. stuff.

Mass to be liftedMass to be lifted

Class 3 Class 3 Levers:Levers:

M.A. of an Incline Plane:

To give this simple machine more mechanical advantage, simply make the ramp longer

Notice: Did the height of the ramp change?

The same amount of work was accomplished with less force on your part!

ForceInput

ForceOutput

The ramp is now longer and less steep

Distance

Work that needs to

be accomplished