Untitled Flashcard Set

Mechanical

Systems

Concept 1.1 - Simple

MachinesIntroduction

● What do you think you already know about

Mechanical Systems?

● What are you hoping to do/learn in this unit?I Can Statement….

● I Can name and describe the 6 simple machinesWhat is a Machine?

● A machine is a device that helps us do workWhat is a Simple Machine?

● A simple machine is a tool or device made up of one

basic machine

○ Eg. Lever, Wedge

● There are 6 simple machines we will be talking about6 Simple Machines

1. Lever

2. Inclined plane

3. Wedge

4. Screw

5. Pulley

6. Wheel and axleLevers

● A lever is a rigid bar or plank that can rotate

around a fixed point called a fulcrum

● They’re used to reduce the force needed to

carry out a task (eg. opening a bottle)

● You can move a larger load than you could

without using it3 Types of Levers

● 1st class

● 2nd class

● 3rd class1st Class Lever

● The fulcrum is between the load and the effort

○ Eg. see saw, scissors2nd Class Lever

● The load is between the effort and the fulcrum

○ Eg. wheelbarrow3rd Class Lever

● The effort is between the load and the fulcrum

○ Eg. shovel, fishing rodInclined Plane

● Think of a ramp

● It allows you to lift a heavy

object using a smaller force

● You have to exert the force

over a larger distanceWedge

● Similar in shape to an inclined plane,

but used differently

● It is forced into an object, usually to

split it apart

● Eg. An axeScrew

● Is essentially a cylinder with a spiral cut

around the outside

● It helps you increase the force you use

● It can turn rotational motion into linear

motionPulley

● Is a rope on a grooved wheel

● They can be made of one or many

wheels, and can be fixed or movable

● They help you lift larger loads than you

could lift on your ownWheel and Axle

● A combination of two wheels of

different diameters that turn together

● Eg. wheel and axle on a car, doorkno

Mechanical Systems

Concept 1.2 - Complex MachinesRecap

● What are the 6 simple machines?I Can Statement

● I Can describe complex machinesComplex Machines

● A device made of several simple machines

(two or more)

● It’s a system in which simple machines all work together

● A system is a group of parts that work together to perform a

function. Eg. a bicycleEg. Bicycle

●Eg. Bicycle

● Within the bicycle are groups of parts that perform specific

functions, such as braking or steering

● These are called subsystems

● All subsystems work together to complete the task that the

complex machine was designed to doSubsystems that Transfer Force

● Subsystems that produce motion can help transfer energy or

force

● In complex machines, these are called linkages and

transmissionsLinkages

● A complex machine moves an object by transferring energy

from an energy source to the object

● The linkage is the part that transfers your energy from the

pedals to the back wheel

● This would be the chainTransmissions

● A transmission contains a number of different gears

● They transfer energy from the engine to the wheels

● They are similar to gears on a bicycle, but they transfer

much larger forces for heavy vehiclesTransmissions

●Gears

● Have a pair of wheels that have teeth that interlink

● Gears transfer energy in one of three ways

1. 3. Transfer energy without changing it

2. Increasing speed and reducing power

Reducing speed and increasing powerGears

● The gear that has a force applied to it from outside the gear

train is the driving gear

● It applies a force to the other gear called the driven gear螺旋状に並んだ螺旋歯車 (Spiral-Shaped Gears in a Spiral Arrangement)Moving uphill, you want a slow gear that is

very powerful (more power, less speed)

Moving downhill, speed is more

Important than power

(less power, more speed

Mechanical Systems

Machines Make Work Easier - Concept 2.1

Mechanical Advantage, Speed Ratio and

EﬃciencyRecap● What is a complex

machine?

●I Can Statement…. ● I Can describe and calculate

mechanical advantage,

speed ratio and eﬃciencyExample● Imagine your car breaks

down on a road trip and you

have a flat tire THAT MUST

BE CHANGED. You have a

spare tire but no car jack.

What do you do?

● Maybe assemble a simple

machine - like a lever - using

a large log and a heavy rockMechanical

Advantage

● Is the amount by which a

machine can multiply a

force

● The force applied to the

machine is called the input

force

● The force the machine

applies to the object is the

output forceMechanical

Advantage

● In the previous example, the

person applies an input

force to the long end of the

lever

● The short end of the lever

applies the output force to

the car

● The output force is much

larger than the input force,

and the car is lifted● Mechanical advantage is a

Mechanical

Advantage meaning

number

● If this number is greater

than 1, the machine will

increase the input force, but

at a lower speed

● If it is less than 1, the

machine will reduce the

input force, but at a faster

speedHow to calculate

Mechanical

Advantage

● The mechanical advantage

is the output force divided

by the input force

● Mechanical advantage is

measured in Newtons (N)Mechanical

Advantage example

● It takes 45 N to lift a 180 N

box with a pulley

(If you lifted it by yourself,

you would have to use 180 N)

● What is the mechanical

advantage of the pulley?Speed Ratio● Speed measures the

distance an object travels in

a given amount of time

● The speed ratio is

calculated by dividing the

input distance by the output

distanceSpeed Ratio

example

● The input distance is 4m.

The output distance is 1m.

What is the speed ratio?Friction ● Friction is a force that

opposes motion

● It can be important in a

mechanical system because

extra force is needed to

overcome friction when you

move an object

● The theoretical and actual

value of mechanical

advantage can be different

because of frictionEfficiency ● Think of a car - fuel

eﬃciency. Why is this

important?

● Is a measurement of how

well a machine or device

uses energy

● Any machine loses some

energy as it operates

● The more energy that is lost,

the less eﬃcient it isEfficiency

● You can calculate the

eﬃciency of a machine by

dividing the mechanical

advantage by its speed ratio

and multiplying by 100Efficiency example● A pulley has a speed ratio of

3 and a mechanical

advantage of 2

● What is its eﬃciency?Assignment● Using the next slide (or

Digital Textbook, go to page

286) answer Questions 2-5.

● Answers can be written on a

blank sheet of paper

Mechanical

Systems

Work - Concept 2.2 NotesRecap

● How do you calculate Mechanical Advantage?

● How do you calculate Speed Ratio?

● How do you calculate Efficiency?I Can Statement….

● I Can describe work input and output for a simple

machineWhat is “Work”?

● What does it mean to do “work”?What is “Work”?

● Work is done when a force acts on an object to

make the object moveWork

● Work is applying a force over a certain distance

IMPORTANT NOTES:

● You need BOTH for work to happen

● They need to be in the SAME directionDecide if each of the

following slides describe

someone doing WORK!Work or Not (Bimba, answers in the notes of the slides)

● You pick a textbook off the ground and put it on

your desk

● Does this count as work?Work or Not

● You carry the textbook from one side of the class

to the other

● Does this count as work?Work or Not

● Your family tries to push a truck out of a ditch. But

it won’t move

● Does this count as work?Work or Not

● You push against a wall with all the strength you

can muster

● Does this count as work?Work or Not

● You study all night for your science test

● Does this count as work?Work

● Is a measure of the amount of force used to move

an object, and it is measured in Joules (J)Calculating Work

● Work = Force x Distance

● Remember that FORCE

○ Is a push or a pull on an object

○ Is measured in Newtons (N)Example

● You exert a force of 50 N to lift your chair onto your

desk. Your desk is 0.4 m high. How much work will

you do?Newton - Meters

● A Newton-meter is the unit of measure when you

multiply force by distance. It is the EXACT same

thing as a JouleExample

● It takes 320 J of work to push a box across the

floor. If the box weighs 40 N, how far will you

have to push the box? (hint: you have to

manipulate the formula

Mechanical Systems

Pressure and Hydraulics - Concept 2.3Recap

● What does it mean to do Work?I Can Statement….

● I Can describe pressure and Pascal’s LawHydraulic Systems

● A hydraulic system uses a liquid under pressure to move a

loadHydraulic Systems

● They increase the mechanical advantage of levers in

machinesPressure in Fluids

● Pressure is a measure of the amount of force applied to a

given area. The unit of measurement is the Pascal (Pa)

p = F/A

p = pressure

F = Force

A = AreaPressure in Fluids

● 1 Pa = the force of 1 Newton over an area of 1m2

● For larger pressures, we use kilo-pascals (kPa) where:

■ 1000 Pa = 1 kPa

● Pressure applied to an enclosed fluid is transmitted equally

in all directions. This is known as Pascal’s LawExamples

● What is the pressure in a container when 60 N of force is

dispersed across an area of 10 m2 ?Examples

● If 2000 N is applied to an area of 50 cm2, what is the

pressure? At a different location within the container, what

can you assume the pressure to be?●A Piston creates Pressure

● In hydraulic systems, pressure is created using a piston

● They can be very large or very small

● Hydraulic devices use a combination of two pistonsA Piston creates Pressure

● The input piston applies force to the fluid, which transfers

this pressure to the output piston

● The pressure transferred to the output piston is equal to the

pressure created by the input piston●Mechanical Advantage in Hydraulic Systems

● You need to know the input and output forces

● If the input is 20 N and the output is 500 N, what is the

Mechanical Advantage?Solving for hydraulic lifts

● The reason that mechanical advantages are so large in

hydraulic lifts is because of the ability of a fluid to transmit

pressure equally

● Recall that p = F/A

● It allows you to use a smaller force on the small piston to

produce a larger force on the large piston●Example

● Assume the small piston has an area of 4cm2 and the force it

applies to the fluid is 20 N

● p = F/A

● What is the pressure of the small piston?Example

● The pressure in the small piston will equal the pressure in the

large piston. Since the area of the large piston will be larger,

the force will also have to be larger. Here’s how to solveExample

●Another Example

● A hydraulic lift has an input force of 10 N and an input piston

with an area of 2m2. The output piston has an area of 5 m2

How much force will the output piston exert