SIMPLE MACHINES

AGENDA Day One Intro to Physics and Simple Machines Review Homework Levers, Wheel and Axle, Pulleys Day Two Review Inclined Plane, Wedge, Screw,

SIMPLE MACHINES

HOME WORK REVIEW

WHAT IS A SIMPLE MACHINE? A simple machine

has few or no moving parts.

Simple machines make work easier

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HISTORY OF WORK

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

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SIMPLE MACHINES

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

How Pyramids were built?

WHAT ARE SIMPLE MACHINES? Early examples that employed simple machinesLargest stones ever movedMoving Large StonesStanding up stonesHow were the pyramids built?Egypt and MesopotaniaNew Theory on Pyramids Building

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SIMPLE MACHINES The six simple machines are:

Lever Wheel and Axle Pulley Inclined Plane Wedge Screw

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SIMPLE MACHINES A simple machine is a device that helps

make work easier to perform by accomplishing one or more of the following functions: transferring a force from one place to

another, changing the direction of a force, increasing the magnitude of a force, or increasing the distance or speed of a force.

MECHANICAL ADVANTAGE?

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MECHANICAL ADVANTAGE It is useful to think about a machine in

terms of the input force (the force you apply) and the output force (force which is applied to the task).

When a machine takes a small input force and increases the magnitude of the output force, a mechanical advantage has been produced.

INPUT FORCE

OUTPUT FORCE

The farther away from the “Fulcrum” is moved from the “Input Force” the greater the Mechanical Advantage is achieved.

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MECHANICAL ADVANTAGE Mechanical advantage is the ratio of output force

divided by input force. If the output force is bigger than the input force, a machine has a mechanical advantage greater than one.

If a machine increases an input force of 10 pounds to an output force of 100 pounds, the machine has a mechanical advantage (MA) of 10.

In machines that increase distance instead of force, the MA is the ratio of the output distance and input distance.

MA = output/input

INPUT FORCE

OUTPUT FORCE

10 lbs

100 lbs

MA = OUTPUT / INPUT

100 ÷ 10 = MA OF 10

SIMPLE MACHINES Simple Machines

can be put together in different ways to make complex machinery

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WORK AND SIMPLE MACHINES

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WHAT IS WORK? In science, the word work has a

different meaning than you may be familiar with.

The scientific definition of work is: using a force to move an object a distance (when both the force and the motion of the object are in the same direction.)

The Force must have cause the object to move, otherwise no work was done.

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WORK OR NOT? According to the

scientific definition, what is work and what is not? a teacher lecturing

to her class workers pushing a

block of stone up and inclined plane

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WHAT’S WORK?

The workers are using a force to move the block of stone a distance. Both the force and the motion are in the same direction

Motion

Force

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WHAT’S WORK? A scientist delivers a speech to an

audience of his peers. A body builder lifts 350 pounds

above his head. A mother carries her baby from room

to room. A father pushes a baby in a carriage. A woman carries a 20 kg grocery bag

to her car?

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WHAT’S WORK? A scientist delivers a speech to an audience of

his peers. NO A body builder lifts 350 pounds above his head. Yes A mother carries her baby from room to room. No A mother pushes a baby in a carriage. Yes A man carries a 20 km grocery bag to his car? No

A STUDENT CARRYING A BOOK DOES NO WORK ON THE BOOK BECAUSE THE FORCE AND MOTION ARE NOT IN THE SAME DIRECTION

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FORMULA FOR WORK

Work = Force x Distance

The unit of force is newtons The unit of distance is meters The unit of work is newton-meters One newton-meter is equal to one joule So, the unit of work is a joule

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W=FD

Work = Force x Distance

Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done?

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W=FD

Work = Force x Distance

Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done? 200 joules(W = 20N x 10m)

ANY TIME A MASS IS LIFTED UPWARD, WORK IS DONE.

Force = 80 Newtons

Distance = 5 Meters

WORK = (80 n)(5 m) = 400 J

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POWER Power is the rate at which work is

done.

Power = Work*/Time *(force x distance)

The unit of power is the watt.

POWER = WORK*/TIME

Force of 80 NewtonsMotion

Distance is 100 Meters

Time is 40 Seconds

WORK (80 n)(100 m) = 8000 JOULES

POWER 8000J/40S= 200Watts

FORMULAS FOR SIMPLE MACHINES Mechanical Advantage – is a ratio of

out put to input Work – Force X Distance, Measured in

joules

Power – Work / Time, Measured in Watts

ARCHIMEDES LEVER

GIVE ME A PLACE TO STAND AND I WILL MOVE THE EARTH

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THE LEVER

A lever is a rigid bar that rotates around a fixed point called the fulcrum.

The bar may be either straight or curved.

In use, a lever has both an effort (or applied) force and a load (resistant force).

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THE 3 CLASSES OF LEVERS The class of a lever

is determined by the location of the effort force and the load relative to the fulcrum.

LEVERS-FIRST CLASS In a first class

lever the fulcrum is in the middle and the load and effort is on either side

Think of a see-saw

LEVERS-SECOND CLASS In a second class

lever the fulcrum is at the end, with the load in the middle

Think of a wheelbarrow

LEVERS-THIRD CLASS In a third class

lever the fulcrum is again at the end, but the effort is in the middle

Think of a pair of tweezers

WHEELS AND AXLES The wheel and

axle are a simple machine

The axle is a rod that goes through the wheel which allows the wheel to turn

Gears are a form of wheels and axles

WHEEL AND AXLE

WHEEL AND AXLE

WHEEL AND AXLE A wheel and axle has a larger wheel (or

wheels) connected by a smaller cylinder (axle) and is fastened to the wheel so that they turn together. When the axle is turned, the wheel moves a greater distance than the axle, but less force is needed to move it. The axle moves a shorter distance, but it takes greater force to move it.Examples: Door Knob, Wagon, Toy Car

PULLEYS Pulley are wheels

and axles with a groove around the outside

A pulley needs a rope, chain or belt around the groove to make it do work

PULLEYS A pulley is a rope, belt, or chain

wrapped around a grooved wheel. Pulleys can be fixed or moveable. The pulley is actually a variation of another simple machine...the lever. A pulley is a circular lever that rotates around its fulcrum.

PULLEYS A pulley that is attached to a structure is

called a fixed pulley. The wheel of a fixed pulley turns, but the pulley itself does not move.

A fixed pulley does not multiply the effort force. The distance you apply the effort is the same as the distance the load moves.

A fixed pulley changes the direction of effort. When you pull down on the rope, the load moves up.

Pulling down is easier than pulling up because you use your body weight when pulling down.

FIXED PULLEYS

PULLEYS A moveable pulley is attached to the object you are

moving. One end of the rope is attached to a fixed structure overhead.

The other end of the rope goes down through the pulley attached to the load and then back up to the top.

Pulling on the other end of the rope causes the load to move up.

The moveable pulley offers a mechanical advantage even though it does not change the direction of effort.

The load is supported by rope on both sides of the pulley, which means that half as much effort is needed to lift the load.

You must exert effort twice as far as the load moves. The force needed to move an object is less, but the distance through which the force must move is longer.

MOVEABLE PULLEYS

MA IS EQUAL TO NUMBER OF ROPES SUPPORTING THE MOVABLE PULLEY

MA OF 1 MA OF 2 MA OF 3 MA OF 4

SINGLE FIXED SINGLE MOVABLE

DAY TWO

*Review Day 1*Inclined Plane*Wedges*Screws*Gears*Class Activity*Review Day 2

REVIEW OF DAY ONE MATERIALS

SIMPLE MACHINES, WORK, FORCE, ENERGY & NEWTON'S THREE LAWS OF MOTION

1. What is a Simple Machine?

2. A simple machine is any device that transmits the application of a force into useful work.

3. SIMPLE MACHINES help us make better use of our muscle power to do WORK.

4. A Machine produces FORCE and controls the direction of Force, it cannot create ENERGY.

WHAT IS MECHANICAL ADVANTAGE?

INPUT FORCE

OUTPUT FORCE

10 lbs

100 lbs

MA = OUTPUT / INPUT

100 ÷ 10 = MA OF 10

Mechanical advantage is the ratio of output force divided by input force. If the output force is bigger than the input force, a machine has a mechanical advantage greater than one.

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WHAT IS WORK? In science, the word work has a

different meaning than you may be familiar with.

The scientific definition of work is: using a force to move an object a distance (when both the force and the motion of the object are in the same direction.)

The Force must have caused the object to move, otherwise no work was done.

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FORMULA FOR WORK

Work = Force x Distance

The unit of force is newtons The unit of distance is meters The unit of work is newton-meters One newton-meter is equal to one joule So, the unit of work is a joule

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WHAT IS POWER? Power is the rate at which work is

done.

Power = Work*/Time *(force x distance)

The unit of power is the watt.

POWER = WORK*/TIME

Force of 80 NewtonsMotion

Distance is 100 Meters

Time is 40 Seconds

WORK (80 n)(100 m) = 8000 JOULES

POWER 8000J/40S= 200Watts

INCLINED PLANES An inclined plane is a

flat surface that is higher on one end

Inclined planes make the work of moving things easier

How were the Pyramids built?

INCLINED PLANE & FRICTION Friction is opposition to motion, so if

nothing is trying to move there will be no friction. However, friction will be present when motion is attempted, even if the object is not yet moving.

There are two different types of friction: static, which acts before the object begins to move, and dynamic, which acts after the object begins moving.

Static friction is usually stronger than dynamic friction.

INCLINED PLANE

INCLINED PLANE . An inclined plane is a flat surface

set at an angle (other than a right angle) against a horizontal surface.

An inclined plane is a simple machine with no moving parts. It is simply a straight slanted surface.

INCLINED PLANE The inclined plane permits you to overcome a

large resistance by applying a relatively small force through a longer distance than the load is to be raised.

The steeper the slant, the more work it takes to go up the inclined plane.

As the slant of an inclined plane decreases, the mechanical advantage increases. It takes less force to raise the object, but the object must move through a longer distance

INCLINED PLANE MECHANICAL ADVANTAGE

To find the MA of an inclined plane, divide its length by its height. MA = length / height

600 METERS LENGTH

100 METERS HEIGHT

600/100 = 6 MA

INCLINED PLANE WORKTo find the WORK of an inclined plane, WORK = Force X Distance

600 METERS LENGTH

100 METERS HEIGHT

600/100 = 6 MA

50n

50n X 600m = 30,000 Joules

WEDGES Two inclined

planes joined back to back.

Wedges are used to split things.

WEDGES A wedge uses force to come between two things. A wedge is

used for three different types of work: connecting (the nail), splitting (the ax), and tightening (the doorstop.)

One end of the wedge tapers to a thin edge and the other end is wide. The longer and thinner a wedge is, the less effort is needed to overcome the resistance force. A very sharp knife requires less effort to cut through a potato because it's blade has been made thinner by sharpening. Try hammering a very thin nail into a block of wood and then try hammering a thick nail into the same block of wood. Which was easier? The thin nail is easier to hammer into the wood because the point of the nail (the wedge) is thinner.

WEDGES

SCREWS A screw is an

inclined plane wrapped around a shaft or cylinder.

The inclined plane allows the screw to move itself when rotated.

SCREW

SCREW Screws are designed to change the direction

of effort. The screw's threads move objects up or

down as the screw turns. When you turn a screw into a piece of wood

in a circle with a screwdriver the screw goes down into the wood.

Circular motion is turned into forward motion. This is how a fan creates a current of air to cool you off on a hot day. The blades of your fan are also a type of screw.

GEARS

SPUR GEARS

HELICAL GEARS

BEVEL GEARS

WORM GEAR

GEAR RATIOCount the gear teeth to determine exact gear ratios - you just count the number of teeth in the two gears and divide. So if one gear has 60 teeth and another has 20, the gear ratio when these two gears are connected together is 3:1.

GEAR ROTATION

When two gears of unequal number of teeth are combined a mechanical advantage is produced, with both the rotational speeds and the torques of the two gears differing in a simple relationship.

MULTI GEAR ROTATION

REVIEW Class activity – In groups find examples

of class I, II, and III levers

Research how to find the MA of an inclined plane that is 100 meters (L) x 20 meters (H)

Complete the Simple Machines Work Sheet

POWER = WORK*/TIME

Force of 60 NewtonsMotion

Distance is 200 Meters

Time is 80 Seconds

WORK (60 n)(200 m) = 12000 JOULES

POWER 12000J/80S= 150 Watts

HEIGHT IS 25 M

MECHANICAL ADVANTAGE200/25=8 MA

BA

C

Gear “B” is rotating “counter clock” wise