Oct.24, 2012You need:Clean paper / pencilHW: Ch.19-1 and your practice problems

Warm Up:What is the formula for work? How can you re-arrange that formula when the question provides work and distance but wants you to find force?

Simple Machines(Making work easier…phew!)

Simple Machines Foldable

• Line up your papers about 1-2 cm apart, so that you see “5, 6, 7, 8” along the bottom.

• Fold the papers over so you see all 8 numbers in a row.

8 Simple Machine Notes

7 Lever

6 Pulley

5 Wheel & Axle

4 Wedge

3 Screw

2 Inclined Plane

1 Simple Machines

By John Smith

Simple Machines Foldable Mrs.Garris will direct Mrs.Garris will direct

you to a station. You you to a station. You will rotate through will rotate through each station on her each station on her mark.mark.

• On each tab, draw On each tab, draw and describe that and describe that type of simple type of simple machine.machine.

• Then give 2-3 Then give 2-3 examples.examples.

8 Simple Machine Notes

7 Lever

6 Pulley

5 Wheel & Axle

4 Wedge

3 Screw

2 Inclined Plane

Draw & Describe:

A sloped surface connecting a lower level to a higher level.Examples:

A boat ramp, wheelchair ramp,propeller, ladder/stairs

What are MACHINES?

• Most people think of complex, technical, Most people think of complex, technical, or electronic gadgets with motors…, but or electronic gadgets with motors…, but machines can be much SIMPLER. machines can be much SIMPLER.

• A machine is any device that lets you do A machine is any device that lets you do WORKWORK in an in an EASIEREASIER or or BETTERBETTER way. way.

• Basically: Basically:

Simple machines make work Simple machines make work EASIER.EASIER.

How do machines do work?

• Machines make work easier by changing 3 things about the FORCE you exert to do work: AMOUNTAMOUNT OF FORCE OF FORCE you exert you exert DISTANCEDISTANCE over which you exert over which you exert

forceforce DIRECTIONDIRECTION in which you exert in which you exert

forceforce

What are SIMPLE MACHINES?

• There are only 6 basic simple machines that make work easier: • Inclined PlaneInclined Plane

• WedgeWedge• ScrewScrew• LeverLever• Wheel & AxleWheel & Axle• PulleyPulley

COMPOUND MACHINES

• Compound Machines – are made of Compound Machines – are made of combinationscombinations of two or more of two or more simple machinessimple machines. .

• For example, a simple can opener is a combination of 3 simple machines: – Lever –Wheel & axle –Wedge

WORK & SIMPLE MACHINES

• Simple machines Simple machines DON’TDON’T change change the amount of the amount of WORKWORK done! done!(They change the size, distance (They change the size, distance or direction of your FORCE!)or direction of your FORCE!)

WORK INWORK IN = = WORK OUTWORK OUT**

(*usually machines lose a bit of (*usually machines lose a bit of work due to work due to FRICTIONFRICTION…)…)

INCLINED PLANE

• An inclined plane is a flat, sloped surface. It connects a lower level to a higher level.

• You use less force over a longer distance to raise a load to a higher level. Input

ForceOutput Force

INCLINED PLANE: Examples

• Ramps (Boat ramps, wheelchair ramps)

• Propeller• Ladders/Stairs

SCREW

• A screw has a “thread” or “groove” wrapped around a central cylinder.

• While turning, it converts a twisting force into a forward or backward force.

Input Force

Output Force

SCREW: Examples & Uses

• Screws can holds things together or lift materials.

• Screws• Screw top lids for jars/bottles• Light bulb• Swivel stools/chairs

WEDGE

• A wedge has slanting slides that meet at an edge – it splits material apart.

• It changes force in one direction into a splitting force that acts at right angles to the blade.

Input Force

Output ForceOutput Force

WEDGE: Examples & Uses

• Ax, Knife, etc.• Zippers

• Used in all cutting machines (to split materials apart)

WHEEL & AXLE

• The wheel is locked to the central axle – when one turns, so does the other one.

• A short powerful force at the axle, will move the wheel’s edge a long distance.

• A long motion at edge of wheel, moves the axle with great force.Input

Force

Output Force

Output Force

Input Force

WHEEL & AXLE: Examples & Uses

• Screwdriver• Windmill• Cars/Bicycles• Rolling Pin• Door Knob• Fan

PULLEY

• A pulley is a grooved wheel with a rope, used to raise/lower/move a load.

• Pulley systems change the direction and/or decrease the input force so you can move heavier loads.

Output

ForceInput Force

Output Force

Input Force

PULLEY: Examples & Uses

• Cranes• Raising a flag on a

pole• Window Blinds• Raising a sail on a

boat• Clothesline

LEVER

• A lever is a bar that pivots or rotates on a point (called a fulcrum).

• Levers may change the size, distance or direction of the force.

LEVERS: Examples & Uses

• First Class Levers:– Scissors, See-saws, Pliers

• Second Class Levers:– Staplers, Nutcrackers, Wheelbarrows

• Third Class Levers– Shovels, baseball bats, tweezers

Machines make work easier by Machines make work easier by changing 3 things about the FORCE:changing 3 things about the FORCE:

• The amount of force

• The distance of the force

• The direction of the force

Machines make work easier by Machines make work easier by changing 3 things about the FORCEchanging 3 things about the FORCE:

• The amount of force(eg. A ramp lets you lift a heavy

object with LESS force)

Machines make work easier by Machines make work easier by changing 3 things about the FORCE:changing 3 things about the FORCE:

• The distance of the force(eg. A baseball bat lets you move your

arms a short distance, but move the end of the bat a large distance).

Machines make work easier by Machines make work easier by changing 3 things about the FORCE:changing 3 things about the FORCE:

• The direction of the force(eg. The pulley on a set of window

blinds lets you move the blinds UP with a DOWNWARD pull.

How do machines make work easier?

In your science notebook, write In your science notebook, write the following questions:the following questions:

• When you add pulleys to a When you add pulleys to a system what happens to the system what happens to the force you need to do work?force you need to do work?

• How can we change a lever to How can we change a lever to make it easier to lift a heavy make it easier to lift a heavy weight? weight?

What is the mechanical advantage of a machine?

• A machine’s mechanical A machine’s mechanical advantage is the number of advantage is the number of times a machine increases a times a machine increases a force exerted on it.force exerted on it.

• Mechanical = Output Force Mechanical = Output Force AdvantageAdvantage Input Force Input Force

What is the mechanical mechanical advantage advantage of a machine?

You exert 10 N of force on You exert 10 N of force on a can opener. The can opener a can opener. The can opener exerts 30 N of force on the exerts 30 N of force on the can. What is the mechanical can. What is the mechanical advantage?advantage?

Mechanical = Mechanical = Output ForceOutput Force = = 30 N30 NAdvantageAdvantage Input Force 10 N Input Force 10 N

Mechanical Advantage = 3Mechanical Advantage = 3

What is the efficiency of a machine?

• The EFFICIENCY compares: The EFFICIENCY compares: – the the workwork you put you put ININ to to – the the workwork the machine puts the machine puts OUTOUT..

• An IDEAL machine is 100% efficient.An IDEAL machine is 100% efficient. INPUT WORK = OUTPUT WORKINPUT WORK = OUTPUT WORK

• In the real world, some input work is In the real world, some input work is always lost due to always lost due to FRICTIONFRICTION between between the moving parts of the machine.the moving parts of the machine.

What is the efficiencyefficiency of a machine?

EFFICIENCY = EFFICIENCY = Output WorkOutput Work x 100% x 100% Input WorkInput Work

You mow the lawn with a rusty You mow the lawn with a rusty lawn mower. You do 50,000 J of lawn mower. You do 50,000 J of work on the lawn mower but only work on the lawn mower but only 25,000 J go to cutting the lawn. 25,000 J go to cutting the lawn. What is the efficiency of the lawn What is the efficiency of the lawn mower?mower?

What is the efficiencyefficiency of a machine?

You mow the lawn with a rusty lawn You mow the lawn with a rusty lawn mower. You do 50,000 J of work on the mower. You do 50,000 J of work on the lawn mower but only 25,000 J go to lawn mower but only 25,000 J go to cutting the lawn. What is the efficiency of cutting the lawn. What is the efficiency of the lawn mower?the lawn mower?

EFFICIENCY = EFFICIENCY = Output WorkOutput Work x 100% x 100% Input Work Input Work

Efficiency = Efficiency = 25,000 J25,000 J x 100% x 100%50,000 J50,000 J

Efficiency = 50%Efficiency = 50%

Try the rest of the practice problems on your own…

Mechanical = Mechanical = Output ForceOutput Force AdvantageAdvantage Input Force Input Force

EFFICIENCY = EFFICIENCY = Output WorkOutput Work x 100% x 100% Input Work Input Work