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Work and Simple Work and Simple MachinesMachines

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What is “work”?What is “work”? In science, the word In science, the word workwork

has a different meaning than has a different meaning than you may be familiar with.you may be familiar with.

The scientific definition of The scientific definition of work is: using a force to work is: using a force to move an object a distance.move an object a distance.

Both the force Both the force andand the the motion of the object must be motion of the object must be in the same direction.in the same direction.

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Work or NOT?Work or NOT? According to the According to the

scientific definition, scientific definition, what is work and what is work and what is not?what is not?

a teacher lecturing a teacher lecturing to her classto her class

a mouse pushing a a mouse pushing a piece of cheese piece of cheese with its nose across with its nose across the floorthe floor

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Work or NOT?Work or NOT? A scientist delivers a speech to A scientist delivers a speech to

an audience of his peers. an audience of his peers. A body builder lifts 350 pounds A body builder lifts 350 pounds

above his head. above his head. A mother carries her baby from A mother carries her baby from

room to room. room to room. A father pushes a baby in a A father pushes a baby in a

carriage.carriage. A woman carries an 8 pound A woman carries an 8 pound

grocery bag to her car.grocery bag to her car.

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Answers:Answers: A scientist delivers a speech to an A scientist delivers a speech to an

audience of his peers. audience of his peers. NoNo A body builder lifts 350 pounds A body builder lifts 350 pounds

above his head. above his head. YesYes A mother carries her baby from room A mother carries her baby from room

to room. to room. NoNo A father pushes a baby in a carriage.A father pushes a baby in a carriage.

YesYes A woman carries an 8 pound grocery A woman carries an 8 pound grocery

bag to her car.bag to her car. No No

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History of Work:History of Work:

Before engines and motors were invented, Before engines and motors were invented, people had to do things like lifting or pushing people had to do things like lifting or pushing heavy loads by hand. Using an animal could help, heavy loads by hand. Using an animal could help, but what they really needed were some clever but what they really needed were some clever ways to either make work ways to either make work easiereasier or or fasterfaster. .

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Simple MachinesSimple Machines

Ancient people invented Ancient people invented simple simple machinesmachines that would help them overcome that would help them overcome resistive forces and allow them to do the resistive forces and allow them to do the desired work against those forces. desired work against those forces.

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Simple MachinesSimple Machines The six simple The six simple

machines are:machines are: Lever Lever Wheel and Axle Wheel and Axle Pulley Pulley Inclined Plane Inclined Plane Wedge Wedge Screw Screw

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1. The Pulley1. The Pulley A pulley is a simple A pulley is a simple

machine that uses machine that uses grooved wheels grooved wheels and a and a roperope to raise, lower, or to raise, lower, or move a load.move a load.

Pulling down on the rope Pulling down on the rope can lift an object can lift an object attached to the rope. attached to the rope. Work is made easier Work is made easier because pulling down on because pulling down on the rope is made easier the rope is made easier due to due to gravitygravity. .

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Everyday Examples:Everyday Examples:PulleyPulley

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2. The Lever2. The Lever A lever is a stiff bar that A lever is a stiff bar that

rotates around a fixed point.rotates around a fixed point. The fixed point is called the The fixed point is called the

fulcrumfulcrum.. The bar may be either The bar may be either

straight or curved.straight or curved. In use, a lever has both an In use, a lever has both an

efforteffort (or applied force) (or applied force) force and a force and a loadload (resistant (resistant force). force).

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Everyday Examples: LeverEveryday Examples: Lever

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3. Wheel and Axle3. Wheel and Axle The wheel and axle is a The wheel and axle is a

simple machine consisting simple machine consisting of a of a largelarge wheel rigidly wheel rigidly secured to a secured to a smallersmaller wheel or shaft, called an wheel or shaft, called an axle. axle.

When either the wheel or When either the wheel or axle turns, the other part axle turns, the other part also turns. One full also turns. One full revolution of either part revolution of either part causes one full revolution causes one full revolution of the other part. of the other part.

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Everyday Examples: Wheel Everyday Examples: Wheel and Axleand Axle

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4. Inclined Plane4. Inclined Plane An inclined plane is an even An inclined plane is an even

slopingsloping surface. surface. The inclined plane makes it The inclined plane makes it

easier to move a weight easier to move a weight from a from a lowerlower to to higherhigher elevation.elevation.

The trade-off is that an The trade-off is that an object must be moved a object must be moved a longer distancelonger distance than if it than if it was lifted straight up, but was lifted straight up, but less forceless force is needed.is needed.

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Everyday Examples: Everyday Examples: Inclined PlaneInclined Plane

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5. Wedge5. Wedge

A wedge is A wedge is two inclined two inclined planes planes joined back to joined back to back (sloping surfaces back (sloping surfaces are outward). are outward).

The wedge is a The wedge is a modification of the modification of the inclined plane. Wedges inclined plane. Wedges are used as either are used as either separatingseparating or or holdingholding devices. devices.

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Everyday Examples: WedgeEveryday Examples: Wedge

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6. Screw6. Screw

An inclined plane An inclined plane wrapped aroundwrapped around a a shaft or cylinder. shaft or cylinder.

This inclined plane This inclined plane allows the screw to allows the screw to move itself or to move move itself or to move an object or material an object or material surrounding it when surrounding it when rotated.rotated.

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Everyday Examples: ScrewEveryday Examples: Screw