WEEK OF NOVEMBER 25-297TH GRADE HOMEWORK-Read Fungi Section 236-241 (Study for Reading Quiz Friday)DUE MONDAY- KINDOM PROTISTA AND KINDGOM FUNGI READING GUIDE.Science Fair Abstract (details Wednesday)

8TH GRADE HOMEWORK-Individual homework due Monday- inventor info! (when you present you can’t use the name of the invention…we will guess what it is based on your description)Build a mousetrap supplies and designQuia quiz in two weeks on PE/KE, power, work, efficiency and simple machinesScience Fair Abstract (Details Wednesday)

What is a Simple Machine? A simple machine has

few or no moving parts. Simple machines make

work easier WE CAN CALCULATE: WORK POWER EFFIECIENCY

LEONARDO DESIGNED MACHINES..http://

www.mos.org/sln/Leonardo/one/one.html

- What Is Work?

The Meaning of WorkWork is done on an object when the

object moves in the same direction in which the force is exerted.

Calculating Power A tow truck exerts a force of 11,000 N to pull a car out

of a ditch. It moves the car a distance of 5 m in 25 seconds. What is the power of the tow truck?

What information have you been given? Force of the tow truck (F) = 11,000 N Distance (d) = 5.0 m Time (t) = 25 s

- What Is Work?

Calculating PowerA tow truck exerts a force of 11,000 N to pull a car out of a ditch. It moves the car a distance of 5 m in 25 seconds. What is the power of the tow truck?What formula contains the given quantities and the unknown quantity? Power= Work/Time Power = (Force X Distance)/TimePerform the calculation. Power = (11,000 N X 5.0 m)/25 s Power = (55,000 N•m)/25 s or 55,000 J/25 s Power = 2,200 J/s = 2,200 W

- What Is Work?

Calculating Power A tow truck exerts a force of 11,000 N to pull a car out

of a ditch. It moves the car a distance of 5 m in 25 seconds. What is the power of the tow truck?

Look Back and Check

Does your answer make sense? The answer tells you that the tow truck used 2,200 W

to pull the car. This value is about the same power that three horses would exert, so the answer is reasonable.

- What Is Work?

Calculating PowerPractice Problem A motor exerts a force of 12,000 N to

lift an elevator 8.0 m in 6.0 seconds. What is the power produced by the

motor? 16,000 W or 16 kW

- What Is Work?

Calculating PowerPractice Problem

A crane lifts an 8,000-N beam 75 m to the top of a building in 30 seconds. What is the crane’s power?

20,000 W or 20 kW

- What Is Work?

- How Machines Do Work

Input and Output Work The amount of input work

done by the gardener equals the amount of output work done by the shovel.

- How Machines Do WorkWhat Is a Machine? A machine makes work

easier by changing at least one of three factors. A machine may change the amount of force you exert, the distance over which you exert your force, or the direction in which you exert your force.

Mechanical AdvantageThe input force and output force for three different ramps are shown in the graph.

- How Machines Do Work

Mechanical Advantage

400 N

Interpreting Data:

If an 80-N input force is exerted on Ramp 2, what is the output force?

- How Machines Do Work

Mechanical Advantage

The slope of each ramp’s graph equals the change in output force divided by the change in input force. This is the formula for mechanical advantage. Ramp 1 has the greatest mechanical advantage.

Drawing Conclusions:

Why does the slope represent each ramp’s mechanical advantage? Which ramp has the greatest mechanical advantage?

- How Machines Do Work

Calculating Efficiency You do 250,000 J of work to cut a lawn with a

hand mower. If the work done by the mower is 200,000 J, what is the efficiency of the lawn mower?

What information have you been given? Input Work (Winput) = 250,000 J

Output Work (Woutput) = 200,000 J

- How Machines Do Work

Calculating EfficiencyYou do 250,000 J of work to cut a lawn with a hand mower. If the work done by the mower is 200,000 J, what is the efficiency of the lawn mower?What formula contains the given quantities and the unknown quantity? Efficiency = Output work/Input work X 100%Perform the calculation. Efficiency = 200,000 J/250,000 J X 100% Efficiency = 0.8 X 100% = 80%The efficiency of the lawn mower is 80 percent.

- How Machines Do Work

Calculating Efficiency You do 250,000 J of work to cut a lawn with a

hand mower. If the work done by the mower is 200,000 J, what is the efficiency of the lawn mower?

Does your answer make sense? An efficiency of 80 percent means that 80 out

of every 100 J of work went into cutting the lawn. This answer makes sense because most of the input work is converted to output work.

- How Machines Do Work

Calculating EfficiencyPractice Problem

You do 20 J of work while using a hammer. The hammer does 18 J of work on a nail. What is the efficiency of the hammer?

90%

- How Machines Do Work

Calculating EfficiencyPractice Problem

Suppose you left your lawn mower outdoors all winter. Now it’s rusty. Of your 250,000 J of work, only 100,000 J go to cutting the lawn. What is the efficiency of the lawn mower now?

40%

- How Machines Do Work

- Simple Machines

Compound MachinesA compound machine is a machine that

utilizes two or more simple machines.

SIMPLE MACHINES

WHEEL AND AXLE

The wheel and axle is a simple machine.  The axle is a rod that goes through the wheel.  This lets the wheel turn.  It is easy to move things from place to place with wheels and axles. 

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

EXAMPLES OF WHEEL AND AXLE

Cars Roller Skates Wagons Door Knobs Gears in Watches, Clocks, and

Bicycles

SIMPLE MACHINES

PULLEYThis simple machine is made up of a wheel and a rope.  The rope fits on the groove of the wheel.  One part of the rope is attached to the load.  When you pull on one side of the pulley, the wheel turns and the load will move.  Pulleys let you move loads up, down, or sideways.  Pulleys are good for moving objects to hard to reach places.  It also makes the work of moving heavy loads a lot easier.  

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

EXAMPLES OF PULLEYS

Flag Poles Clothes Lines Sailboat Blinds Crane