Simple Machines

Simple Machines

So far this semester, you've learned a ton about certain things, which are all classified under certain major topics:

 

1) Distance/Displacement
2) Speed/Velocity
3) Acceleration/Gravity
4) Work/Force
....and other stuff.

 

A fair question to ask at this point is, "Where's this all going?"

​Physics so far.....

We're surrounded every day by machines. We use them every day, and I'm not referring to the cell phones you can barely take out of your hands.

 

I'm referring to real machines, the ones that we'd have a much lower standard of living without.

 

Imagine life without this:

​Here's Where:

Reality is that the internal combustion engine is nothing more than a combination of six simple machine types that were first defined by Leonardo da Vinci.

 

The physics principles that we've studied up until this time allow us to define almost all machines, since almost all are just combinations of Leonardo's machine types.

​Physics Reality:

• Machines provide mechanical advantage, which is a measurement of the the amount the machine amplifies force.

• In an ideal machine (without friction), input work and output work are equal. 

• Effort is the work that you do.

• Resistance is the work done on the object you are trying to move.

• Although the amount of work is the same with the machine or without it, the purpose of the machine is to do that work by lowering effort.

• Efficiency is a measure of how well the machine lowers that effort.

What is the Purpose of a Machine?

​How Do We Measure Mechanical Advantage and Efficiency?

​The Ideal Mechanical Advantage (IMA) of a machine is the ratio between the two distances moved:

​However, the mechanical advantage is limited by friction.  So, the Actual Mechanical Advantage (AMA) is the ratio of the forces responsible for the distances moved:

​Finally, we measure the Efficiency of the machine by calculating the ratio between the AMA and the IMA.

​So, what are these Six Simple Machines?

https://sfisd-my.sharepoint.com/:v:/r/personal/michael_craney_sfisd_org/Documents/DL%20-%20Physics/Week%2014/Simple%20Machines%20Animation.mp4?csf=1&web=1&e=h0xbWP

or
​https://youtu.be/s03LgyIgCtw?si=GjBa7eI2zP4I7ELe

​Wheel and Axle

​Wait, what?

Multiple Choice

If the 6" diameter axle on a car turns a 24" diameter wheel, what is the mechanical advantage?

• 4
• 8
• 2.5

• .25

Multiple Choice

What is the mechanical advantage of of a wheel

and axle if the radius of the wheel is

100cm and the radius of the axle is 10cm?

• 100
• 10
• 50
• 5

Multiple Choice

The mechanical advantage of a wheel and

axle is 5. The radius of the wheel is 10.

What is the radius of the axle?

• 3
• 7
• 12
• 2

Next: The Pulley

​Watch the video and work on the simulation on the next page
https://interactives.ck12.org/simulations/physics/block-and-tackle/app/

Interactive Simulation

• Click the arrow to the right of the screen to enter the simulation
  
  

• Click TUTORIAL at the top, and watch the video.
  
  

• Finally, watch https://youtu.be/vSsK7Rfa3yA?si=FQ3VU1apZr4bgZD4 up until the 7:25 mark.

Calculating MA for Pulleys

For a simple pulley, (Image, left) the
calculation for MA is simple:
MA = 2N
where "N" is the number of pulleys in the machine.

For a complex pulley (Image, right), where the
wheels are attached to each other, the
calculation is also simple:
MA = 2^N

Next: Inclined Plane (or, Ramp)

Watch the Video:
​https://youtu.be/5c4J_PW9wsg?si=JP5XG3CpUtQ0yNzn

​The Screw

​Watch the video at:
https://youtu.be/D2LGkqp_y7g?si=6-OTntDRmm-vamhL

Multiple Choice

A screw has a diameter of 0.25 centimeters and has 10 threads per centimeter. What is the ideal mechanical advantage of the screw?

• 2.5
• 7.85
• 0.25
• 5.0

Multiple Choice

A screw has a head diameter of 3/16 of an inch and has 5 threads per inch. What is its mechanical advantage?

• 2

• 4.5

• 3.1416

• 2.9

Multiple Choice

Determine the mechanical advantage for a screw with a 0.91 cm diameter and 28 threads to 1.0 cm.

• 0.91
• 28
• 1.0
• 80

A wedge is two inclined planes back to back. Like an inclined plane, the IMA of a wedge is the ratio between the length of the wedge and the width of the wedge. Unlike an inclined plane, a wedge does not have a right angle; the IMA of a wedge cannot be found with sines.

A wedge applies more force to the object (output force) than the user applies to the wedge (input force), so the mechanical advantage of a wedge is greater than 1. A longer, thinner wedge has a greater mechanical advantage than a shorter, wider wedge. With all wedges, the trade-off is that the output force is applied over a shorter distance, so force may need to be applied to the wedge repeatedly to push it through the object.

​

​The Wedge

​Watch the Video:
https://www.youtube.com/watch?v=No5Df2231YA&t=2s

A lever consists of a flat plane placed over a fulcrum. The resistance is the object to be moved (shown here in red), and is placed to one side of the fulcrum. The resistance distance in a lever is called the resistance arm. The effort is exerted elsewhere on the lever, and the effort distance is called the effort arm or effort lever arm. The lever shown here is the most common type of lever, a Class One Lever, but there are two other types of levers.

​The Lever

​Types of Levers

Effort work = effort force X effort lever arm.
Resistance work = Resistance force X Resistance lever arm

Suppose the resistance force is 500. N, the resistance arm is 0.400 m, and the effort arm is 0.800m. We can calculate exactly how much effort force is required to lift the resistance in this system:

Lever Calculations

​Watch the Video:
https://youtu.be/n7dUtwejenQ?si=TV-lIhO18PzNDGlI

Effort work = effort force X effort lever arm.
Resistance work = Resistance force X Resistance lever arm


Mechanical Advantage = Effort Arm Length / Resistance Arm Length

Mechanical Advantage = Load / Effort

More Lever Formulas

Effort work = effort force X effort lever arm.
Resistance work = Resistance force X Resistance lever arm

More Lever Calculations

​Watch the Video:
https://youtu.be/n7dUtwejenQ?si=TV-lIhO18PzNDGlI

Multiple Choice

In a lever, the effort arm is 60 cm and resistance arm is 40 cm. Find its mechanical advantage:

• 0.5
• 2
• 3
• 1.5

Multiple Choice

A crowbar of length 120 cm has its fulcrum situated at a distance of 20 cm from the load. Calculate the mechanical advantage of the crowbar.

• .167

• 4

• 6

• 5

Multiple Choice

A pair of scissors has its blades 15 cm long, while its handles are 7.5 cm long. Find its mechanical advantage:

• 2
• 15
• 7.5
• 0.5

Multiple Choice

If the mechanical advantage of a lever is 10, Find the effort required to lift a box weighing 2500 N.

• 100 N
• 250 N
• 500 N
• 25 N

Multiple Choice

If a lever has a mechanical advantage of 0.5, and a person weighing

600 N sat on the effort arm, how heavy of a

person could be lifted who sat on the other end?

• 300 N
• 900 N
• 1200 N
• 600 N

Multiple Choice

A force of 50 N is required to cut a metal sheet. A shears used for

cutting the metal sheet has its blades 5 cm long, while its

handle is 10 cm long. What effort is needed to cut the sheet?

• 5 N
• 10 N
• 15 N
• 25 N

DONE? Great. Now go back and do the videos you skipped.