Uploaded by islamzafar

Simple Machines Slides Practice01 (1)

advertisement
Practice #1—Introduction to Machines
Machines
Mr. Burleson
[email protected]
1
Agenda
Introduction and Rules
Basics of Simple Machines
Simple Machines Practical
Homework
*huge thanks to Alan Chalker (National
Physics Chair) and Roger Demos (National
Event Supervisor) for their support
2
Tips for
Science Olympiad
Study often because all the work is done by you!
Use Teamwork for studying and practicing
Use the references, homework, and homework generators to
practice
Know the rules better than anyone.
Check the national website often for updates and FAQs.
Practices are for covering material, sample tests, and practicing
measurements—studying should be done at home
More practice will lead to better results
3
Introduction and Rules
Come prepared to practices with completed
homework and all your questions
Listen and participate.
Be willing to study on your own and do more work
than assigned
4
Machine Practice Timing
Recommendations
Each Practice should be an hour to an hour and a half,
once a week.
15 minutes—Grading homework.
30 minutes—Learning Lesson of the Day
15 minutes—In Practice quick test on Lesson of the Day
25 minutes—Practical testing
5 minutes—Sending out homework
Each student who misses Practice should get the
notes and homework to be ready for the next
Practice or they will receive zeros for both.
5
Machines (B)
Rules
Team of 2
No Eye Protection Required
Device must be impounded
Part 1 (Written Test)
45% of score
Simple Machine Concepts
Simple Machine Calculations
Simple Machine History is no
longer included
Part 2 (Device Testing)
55% of score
Two Ratio Scores (15% each)
One Time Score (15%)
Chart Score (10%)
Only five types of machines
Levers (all three classes)
Inclined Plane
Wedge
Pulley (up to two double
pulleys)
Wheel and Axle
Prohibited topics
Compound machines
Dynamic Calculations
Material Strengths
Potential/Kinetic Energy
Coefficient of Friction
Screw Simple Machines
Angle of Repose
6
Machines (C)
Rules
Team of 2
No Eye Protection Required
Device must be impounded
Part 1 (Written Test)
45% of score
Sim/Compound Machine
Concepts
Sim/Compound Machine Calcs
Sim/Compound Machine History
is no longer included
All six types of simple machines
Levers (all three classes)
Inclined Plane
Wedge
Pulley (up to two double
pulleys)
Wheel and Axle
Screw
Prohibited topics
Dynamic Calculations
Material Strengths
Angle of Repose
Part 2 (Device Testing)
55% of score
Two Ratio Scores (15% each)
One Time Score (15%)
Chart Score (10%)
7
Scoring for
Machines
Exam Score (ES) is worth maximum 45 points (45 points awarded to highest test score)
Time Score (TS) = ((240-time)/240*15 points (max 15 points)
Ratio Score (R1 and R2)=(1-(abs(AR-MR)/AR))*15 points (max 2x15 = 30 points)
Chart Score (CS) is worth 10 points (max 10 points)
2 points for including data spanning the possible mass range
2 points for including at least 10 data points in each data series
2 points for proper labeling (e.g. title, team name, units)
2 points for distinct graphs (0.5 points each up to 2 points)
2 point for including a labeled device diagram
Violations
Competition violate TS, R1, and R2 are multiplied by 0.9
Construction violation, if resolved during competition block or miss impound TS, R1, and R2 are multiplied by 0.7
Team with no device, no ratio estimate or do not make an HONEST attempt TS, R1, and R2 all marked zero
Final Score (FS)=ES+MS+TS+CS (maximum of 100 points)
Tie Breakers
1.
Best ES score
2.
Best TS score
3.
Best R1
4.
Best R2
8
Your Binder is Your
Lifeline
2” binder is new rule
A good binder is like having an open book
test
Use your binder in all studying, practices,
and at tournaments
Always build your own binder in case
something happens to your partner’s
First page should be the rules, so you can
find them quickly
Always have easy to read tables for
constants, materials, and equations
Organize into sections that work for you
and your teammate with tabs for easy
finding
Focus on the things you have to look up or
don’t understand
Include other tests with keys and work
shown
When you have two or more
pictures of the same thing, include
ALL of them (often Event
Supervisors will get diagrams and
samples from the internet)
When you solve a difficult problem,
show all your work and put that in
the binder to help remind you how
you solved that difficult problem
Keep the binder small enough to be
useful, but big enough to be
comprehensive
Test you skills at finding things in
the binder each practice so that it
takes no more than 10 seconds to
find anything
Make sure you can read it (good
fonts)
Use sheet protectors when possible
9
Basics of Simple
Machines
Lever
Inclined Plane
Wheel and Axle
Wedge
Pulley
Screw, not included in
Simple Machines (B)
10
Basic Definition of Simple
Machines
A simple machine is an elementary device that has a
specific movement (often called a mechanism),
which can be combined with other devices and
movements to form a machine.
The idea of a "simple machine" originated with the
Greek philosopher Archimedes around the 3rd century
BC, who studied the "Archimedean" simple machines:
lever, pulley, and screw
Thus simple machines are considered to be the
"building blocks" of more complicated machines.
A bicycle has wheels, levers, and pulleys
11
Mechanical Advantage
A simple machine has an applied force (or effort)
that works against a load force.
If there are no friction losses, the work done on the
load is equal to the work done by the applied force.
This allows an increase in the output force at the cost
of a proportional decrease in the distance moved by
the load.
The ratio of the output force to the input force is the
mechanical advantage of the machine.
12
Efficiency
Machines lose energy through friction, deformation
and wear, which is dissipated as heat.
This means the power out of the machine is less than
power in.
The ratio of power out to power in is the efficiency η
of the machine, and is a measure of the energy
losses.
13
What is a Lever?
A lever is a machine consisting of a beam or rigid rod
pivoted at a fixed hinge, or fulcrum
The word comes from the French lever, "to raise", cf. a
levant.
A lever amplifies an input force to provide a greater
output force, which is said to provide leverage.
The ratio of the output force to the input force is the
ideal mechanical advantage of the lever.
14
Classes of Levers
Class 1: Fulcrum in the middle: the effort is
applied on one side of the fulcrum and the
resistance on the other side
A crowbar or a pair of scissors.
Class 2: Resistance in the middle: the effort
is applied on one side of the resistance and
the fulcrum is located on the other side.
A wheelbarrow, a nutcracker, a bottle opener or
the brake pedal of a car. Mechanical advantage is
greater than 1.
Class 3: Effort in the middle: the resistance
is on one side of the effort and the fulcrum
is located on the other side
A pair of tweezers or the human mandible.
Mechanical advantage is less than 1.
15
IMA of Lever/Law of the
Lever
If a and b are distances from the
fulcrum to points A and B and let
the force FA applied to
A is the input and the force FB
applied at B is the output, the
ratio of the velocities of points A
and B is given by a/b, so we have
the ratio of the output force to
the input force, or mechanical
advantage, is given by
16
In Practice Quiz
Think of as many levers you can, including around the
house, construction sites, school, etc.
Workshop tools
Garden tools
Kitchen tools
Think of as many places where you can lose
efficiency with a lever
17
Things to consider
Winners prepare
Event Supervisors are volunteers
No one knows this material
naturally, those that prepare the
best will do better.
They have given up their time to
prepare for the competition, run
the event, score, etc.
Study and do homework before
practice, use practice for asking
questions
Some are more experienced than
others
Plan on doing work on this a few
times a week in addition to
practice
Winners work together
Be a good partner
Work off each other strengths
Practice together
Some know the rules more than
others
Be respectful and work with them
Always listen to instructions and
read the test before you ask your
questions
Different Event Supervisors ask the
same question differently
18
Arguing an Illegal
Question
Always make sure you read the question again to ensure it really is illegal.
Event supervisor might have old rules, but double check your rules first.
Ask for how to implement the question within the rules.
Remove the illegal items like capacitors/inductors/LEDs/etc.
Operate it as DC instead of AC.
Reference the specific rule, normally in section 3.d
Semiconductors include diodes, LEDs, transistors, OpAmps, and integrated
circuits. LEDs, Diodes and OpAmps are now allowed in certain
circumstances.
AC circuit theory includes frequency analysis, two or three phase power,
capacitor/inductor reactance. But they can sometimes be made legal by
switching to a DC system.
AC devices include transformers, rectifiers, others. Most will not work
with DC.
Several items are only available for Division C and not for B
19
Practical
Each team will use a ruler and several small objects.
If you have something to balance the ruler on top of you can
use that as your fulcrum, otherwise use your finger
First, balance the ruler on the fulcrum point
Is the balance point near the middle of the ruler
Note when the ruler is not near the balance point, how does
it rotate
Second, start with the balanced ruler and then have the
second person put two of the same small objects on the
ruler to find where they balance
Third, start with a balanced ruler and then have the
second person put two different small objects on the ruler
to find where they balance
20
Suggested References
Websites:
•
•
•
•
Soinc.org Simple Machines/ Complex Machines Event pages
Scioly.org student forums / wiki / test exchange
Wikipedia (Simple Machines, Levers, Pulleys, etc.)
http://www.khanacademy.org/#Physics
Khan Academy Tutorial on Mechanical Advantage
Museum of Science and Industry Simple Machines online game
SEDL Simple Machines Online Textbook
Department of Navy - Basic Machines Textbook
21
How to use the
Homework Generator
Homework generator is a Microsoft Excel workbook with multiple
tabs
The tabs are broken down into levels (start with Level 1 and work your
way up)
Work on accuracy first, so don’t start Level 2 until you can you do all of
Level 1 with 100% accuracy at least three whole sheets
A good way to improve speed is to see how many problems or sheets you
can do in 5 min (after you are accurate)
Some tabs have reference material, but most only have problems
The numbers used in problems are from a random number generator
If on a Windows machine you can refresh using F9
You can also refresh by reopening the workbook, printing, or saving the
file
Every time it is refreshed it randomly comes up with new problems and
corresponding answer sheets.
22
Homework #1
Do the Homework Generator problems for Levers
Level 1
Go through the house and write down as many of the
six simple machines as you can at home.
We will study more levers next in depth.
23
Download