work, mechanical advantage, & simple machines making jobs easier
TRANSCRIPT
Work, Mechanical Advantage, & Simple Machines
making jobs easier
Journal Entry
What is work?
Is there anyway to make work easier? How?
Work Demonstration
Moving Pennies… Any Volunteers?
How does the science of physics define work???
Work
Definition:
Work is done on an object when a force is exerted on an object that causes the object to move some distance. No work without motion No work without force in the same direction
Work is the way we transfer energy
Equation: Work = force X distance
Force
A push or a pull
Measured in metric unit of Newtons One Newton = ~1/5 lbs Tool: spring scale Demo Spring Scale
Motion and force
Person does not work on weights – weights do not move
Person does work on weights – weights moved
Force on weights
Force on weights
Summer Olympics 2000 Sydney Australia By Lou Jones
http://www.pricespower.com
Direction and force
Horse does not work on the rider – force not in same direction
Horse does work on the cart - force and motion in the same direction
Force on person
motion motion
Force on cart
Calculating work
Work = Force X Distance F = Force units = Newton, N d = Distance units = meter, m W = Work units = Joule, J
J = N x M Joules = Newton x Meter Work = Force x Distance
1 Joule = 1 Newton-meter
NASA Video
http://www.youtube.com/watch?v=iCqm5uxc2dE&feature=related
Show ~ 3:30
Calculating work
Work = Force X Distance F = Force units = Newton, N d = Distance units = meter, m W = Work units = Joule, J
J = N x M Joules = Newton x Meter Work = Force x Distance
1 Joule = 1 Newton-meter
Conversion: 1kg = 9.8N (You must memorize this conversion)
Practice Calculating Work
If you moved a pencil 20 meters using 2.5 Newtons of force, how much work have you done?
W = F x d
Practice Calculating Work
A force of 800 N is needed to push a car across a lot. If a student pushes the car 40.0 m. How much work is done?
Practice Calculating Work
How much work is done in lifting a 60.0-kg person a vertical distance of 10.0 m? (remember: 1kg = 9.8 N)
Practice Doing Work
If you exert a force of 5 N on a stack of 20 textbooks that had a mass of 5.10 kg (about 11 pounds) 1 meter, how much work have you done? (remember: 1 kg = 9.8 N)
Ugh! Too much work!
Want help?
Simple Machine: Examples
Why do we use machines?
to reduce the amount of effort or work we exert
to increase our ability to lift or move objects.
Kinds of Machines
Simple Machines Lever, wheel & axle, pulley, inclined plane, screw, wedge Few or no moving parts
Compound Machines Consists of two or more simple machines
Simple Machine Families
Inclined Plane Family wedge, inclined plane (ramp), screw
Lever Family lever, wheel and axle, pulley
Simple Machines & Work
A machine… is a device that does work does not increase amount work done makes it easier to do the same amount of work.
Machines make work easier by … changing force changing distance changing the direction of the force.
Machines…
Do NOT change the amount of work done
Total work does not change
Work = Force x Distance
If a machine allows you to…
force, then distance
distance, then force
apply a force in a different direction, then it doesn’t change how much force you have to apply or how far you move it
Mechanical advantage
# of times a force exerted on machine is multiplied by the machine
Mechanical advantage or MA = Output force
Input force
If MA > 1, then force, but distance
If MA < 1 , then force, but distance
If MA = 1, then neither the force or distance is changed.
Eureka! Video: Mechanical Advantage
http://www.youtube.com/watch?v=oWiZ_5qvs7I&NR=1
Hey, It’s Tim and Moby
http://www.brainpop.com/science/motionsforcesandtime/work/
Attack of the Machines!!!
Mechanical Advantage: Simple Machines
You will learn about the MA of specific simple machines when each new machine is introduced.
Types of simple machines
Inclined plane
Wedge
Screw
Lever
Wheel and axle
pulley
Image taken from:http://www.daniel-wright.district103.k12.il.us/ccheifetz/physics.html
Inclined plane
teacher.scholastic.com/dirtrep/
simple/img/plane.gif
Wedge
teacher.scholastic.com/dirtrep/
simple/img/wedge.gif
Screw
teacher.scholastic.com/dirtrep/
simple/img/screw.gif
Lever
teacher.scholastic.com/dirtrep/
simple/img/lever.gif
Wheel and axle
teacher.scholastic.com/dirtrep/
simple/img/wheel.gif
Pulley
teacher.scholastic.com/dirtrep/
simple/img/pulley.gif