Work Work – The movement of an object – The movement of an object by a force.by a force.

WorkWork = Force x Distance = Force x Distance

JouleJoule = 0.74 ft*lb = 0.74 ft*lb

Used to describe work.Used to describe work.

You decide to lift a 200 lbs dumbbell You decide to lift a 200 lbs dumbbell from the ground to over your head. from the ground to over your head. The dumbbell will travel 7 feet. How The dumbbell will travel 7 feet. How

much work did you do?much work did you do?

1400 ft*lb1400 ft*lb

1,036 joules1,036 joules

Power = Work / TimePower = Work / Time

Horsepower Horsepower - Unit used to express - Unit used to express power. power.

Based on the estimation a horse Based on the estimation a horse could lift 550 pounds a distance of could lift 550 pounds a distance of

one foot in one second.one foot in one second.

A weed eater uses 4400 ft*lb/sec of A weed eater uses 4400 ft*lb/sec of power, how many horsepower does power, how many horsepower does

it have?it have?

8hp8hp

Machines Machines – Devices for doing work.– Devices for doing work.

Simple Machines Simple Machines – Basic force multiplying – Basic force multiplying machines.machines.

Can help us byCan help us by::

1.1.Multiplying the force applied to them.Multiplying the force applied to them.

2.2.Changing the direction of the force applied to Changing the direction of the force applied to them.them.

3. Multiplying the speed or distance that the applied 3. Multiplying the speed or distance that the applied force moves something.force moves something.

Effort (E) Effort (E) – The force we apply to the – The force we apply to the machine.machine.

Resistance (R) Resistance (R) – The force the machine helps – The force the machine helps us overcome.us overcome.

Mechanical Advantage (MA) Mechanical Advantage (MA) – Tells us the – Tells us the number of times a machine multiplies our number of times a machine multiplies our

effort.effort.

MA = Resistance / EffortMA = Resistance / Effort

3 men use a pulley system to lift a 1500 pound 3 men use a pulley system to lift a 1500 pound cargo container. The men use 125 pounds of cargo container. The men use 125 pounds of

effort, how much does the pulley system effort, how much does the pulley system multiply the men’s effort?multiply the men’s effort?

12 Times 12 Times

Work Input Work Input – The work put into a machine.– The work put into a machine.

Work Input = Effort Distance X Effort ForceWork Input = Effort Distance X Effort Force

Work Output Work Output – The work received from a – The work received from a machine.machine.

Work Output = Resistance Distance X Work Output = Resistance Distance X Resistance ForceResistance Force

Law of Work Law of Work – Work put into a machine is – Work put into a machine is equal to the work received from the machine equal to the work received from the machine

under ideal conditions. under ideal conditions.

Effort Force x Effort Distance = Resistance Force x Effort Force x Effort Distance = Resistance Force x Resistance DistanceResistance Distance

Work Input = Work OutputWork Input = Work Output

Because of friction, no machine has ever been Because of friction, no machine has ever been made that can produce exactly as much work made that can produce exactly as much work

as applied to it.as applied to it.

Work Input is always greater than work Work Input is always greater than work output.output.

Although the work input is greater than the Although the work input is greater than the work output, no energy is lost, its just work output, no energy is lost, its just

converted to other forms such as heat or converted to other forms such as heat or sound.sound.

Work Input = Work Output + Work Used to Work Input = Work Output + Work Used to Overcome FrictionOvercome Friction

6 Types of Simple Machines6 Types of Simple Machines-LeverLever

-Wheel and AxleWheel and Axle-PulleyPulley

-Inclined PlaneInclined Plane-WedgeWedge-ScrewScrew

LeverLever

Can multiply the force or speed with or Can multiply the force or speed with or without changing the direction of the effort.without changing the direction of the effort.

FulcrumFulcrum

The pivot point upon which the beam of a The pivot point upon which the beam of a lever rests.lever rests.

First Class LeversFirst Class Levers

Input and output forces are on either side of Input and output forces are on either side of the fulcrumthe fulcrum

Effort ArmEffort Arm

The end of the lever that the effort force is The end of the lever that the effort force is applied to.applied to.

Resistance ArmResistance Arm

The arm of the lever that moves by The arm of the lever that moves by overcoming the resistance force.overcoming the resistance force.

If the effort arm is longer than the resistance If the effort arm is longer than the resistance arm the force will be multiplied.arm the force will be multiplied.

If the effort arm is shorter than the resistance If the effort arm is shorter than the resistance arm the speed will be multiplied.arm the speed will be multiplied.

Second Class LeversSecond Class Levers

Fulcrum is at one end of the lever, effort is applied at Fulcrum is at one end of the lever, effort is applied at the other end, and the resistance is between the the other end, and the resistance is between the

effort and the fulcrum.effort and the fulcrum.

Always multiply the effort force and do not change Always multiply the effort force and do not change its direction.its direction.

Third Class LeversThird Class Levers

Fulcrum is at one end of the lever, resistance at the Fulcrum is at one end of the lever, resistance at the other end, and the effort force is applied between the other end, and the effort force is applied between the

fulcrum and the resistance.fulcrum and the resistance.

Always multiply distance and speed without Always multiply distance and speed without changing the direction of the effort force.changing the direction of the effort force.

Mechanical Advantage = Effort Arm / Mechanical Advantage = Effort Arm / Resistance ArmResistance Arm

Mechanical Advantage = Effort Distance / Mechanical Advantage = Effort Distance / Resistance DistanceResistance Distance

Mechanical Advantage = Resistance Force / Mechanical Advantage = Resistance Force / Effort ForceEffort Force

If we want to lift a 120 pound rock with a lever If we want to lift a 120 pound rock with a lever that gives us a mechanical advantage of 12, that gives us a mechanical advantage of 12, how much force do we have to exert under how much force do we have to exert under

ideal conditions (without friction)?ideal conditions (without friction)?

10 pounds10 pounds

If we wanted to lift this rock 5 feet, over what If we wanted to lift this rock 5 feet, over what distance would we have to exert this force?distance would we have to exert this force?

60 feet60 feet

Wheel and Axle – Wheel and Axle – Basically, a circular lever.Basically, a circular lever.

Axis of rotation is fulcrum.Axis of rotation is fulcrum.

Axle and large wheel correspond to the arms.Axle and large wheel correspond to the arms.

Mechanical Advatange Mechanical Advatange = Input Radius / = Input Radius / Output RadiusOutput Radius

A bicycle wheel has an input radius of 12 A bicycle wheel has an input radius of 12 inches, and an output radius of 4 inches. inches, and an output radius of 4 inches. What is the mechanical advantage of the What is the mechanical advantage of the

wheel and axle?wheel and axle?

PulleyPulley – A simple machine consisting of a – A simple machine consisting of a grooved wheel over which a rope or cable grooved wheel over which a rope or cable

passes.passes.

Fixed Pulley – Fixed Pulley – A pulley that does not move A pulley that does not move with resistance. with resistance.

Does not multiply effort force, merely Does not multiply effort force, merely reverses it.reverses it.

Movable Pulley – Movable Pulley – A pulley that is attached to A pulley that is attached to the resistance and moves with it.the resistance and moves with it.

Allows the effort force applied (discounting Allows the effort force applied (discounting friction) to be only half of the resistance force.friction) to be only half of the resistance force.

Block and Tackle Pulley – Block and Tackle Pulley – A combination of one or A combination of one or more fixed pulleys and one or more movable more fixed pulleys and one or more movable

pulleys.pulleys.

Movable pulleys are used to multiply the effort force Movable pulleys are used to multiply the effort force while the fixed pulleys are used to change the while the fixed pulleys are used to change the

direction of the effort force.direction of the effort force.

Mechanical Advantage = Number of rope segments Mechanical Advantage = Number of rope segments supporting the resistance.supporting the resistance.

Inclined PlaneInclined Plane – A sloping platform that – A sloping platform that enables us to move an object to a higher enables us to move an object to a higher

position without having to lift it straight up.position without having to lift it straight up.

Mechanical Advantage = Effort Distance / Mechanical Advantage = Effort Distance / Resistance DistanceResistance Distance

If a block and tackle pulley system has 8 If a block and tackle pulley system has 8 segments of ropes supporting a log, what is segments of ropes supporting a log, what is

the mechanical advantage of the pulley the mechanical advantage of the pulley system?system?

88

Wedge Wedge – A special form of an inclined plane.– A special form of an inclined plane.

Modifies force and changes its direction to Modifies force and changes its direction to the sides.the sides.

Mechanical Advantage = length / thickness.Mechanical Advantage = length / thickness.

John uses a 10 inch long ax head that is 4 John uses a 10 inch long ax head that is 4 inches thick. What is the mechanical inches thick. What is the mechanical

advantage of the wedge.advantage of the wedge.

44

Screw Screw – Spiral form of an inclined plane.– Spiral form of an inclined plane.

Apply force in the direction of their axis as Apply force in the direction of their axis as they are turned.they are turned.

Pitch Pitch – The distance across two of the ridges – The distance across two of the ridges or thread’s on the screw’s shart.or thread’s on the screw’s shart.

Mechanical Advatange = 2 r / PitchMechanical Advatange = 2 r / Pitch

What is the mechanical advantage of a screw What is the mechanical advantage of a screw that has a radius of 6 inches and a pitch of 4 that has a radius of 6 inches and a pitch of 4

inches?inches?

33

Efficiency = Work Output / Work Input x 100 %Efficiency = Work Output / Work Input x 100 %

A machine has a work output of 4 A machine has a work output of 4 joules, and a work input of 5 joules. joules, and a work input of 5 joules.

What is the efficiency of the What is the efficiency of the machine?machine?

80 %80 %