work, mechanical advantage, & simple machines making jobs easier

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

Eureka Video: What is Work?

Eureka Video: Work

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