Chapter Three : work and simple machines

Lesson 1: Work and Power What is work? Work is the transfer of ________to an object by a force that makes an object __________________ of the force. Work is only being done while _______________ _______________________ You push makes your bike move= work is _______ You push on the bike and it does not move= ____ work is done

Calculating Work Work equation Work (in ______) = _______(Newton) x ________ (meter) W = Fd A joule unit is equal to a _____________ The joule is the SI unit of _____ and _______ The distance is the distance the object moves while ______________________________

Factors That Affect Work The work done on an object depends on the direction of the ______applied and the direction of _________ A force that acts in the direction of the motion __________________ Force and motion are in the same direction Multiply the force and the distance

Lifting Objects _______your backpack requires you to do work Backpack has _________ because of the gravity To lift, you must pull with an upward force greater than the weight The work done to lift any object is equal to the _______ of the object multiplied by the ____________it is lifted

Work and Energy Doing work on an object transfers energy to the object Kinetic energy- ________________________ Figure 4 on page 90 Boy applies a force on the tray to make it move; ___________________ This work ____________energy to the tray The added energy is the ____________ energy of the tray

Work and Energy Lifting an object also increases the object’s energy ______________________________(GPE) Energy of the object increases as its __________ increases Girl lifts the tray: did work on the tray GPE __________and it ________kinetic energy as it moves _____________ Transferred energy to the tray which ___________ the tray’s ___________and _____________energy

What is power? Power is the ______________________________ More quickly=more ___________ Power (in _______) = ________(in joules) / _________(seconds) P= W/t The SI unit of power is the watt (______). 1 J/s = 1 W Work transfers energy Power is the rate at which _______ is transferred to an object

Find Power A boy does 18 J of work in 2.0s on his backpack as he lifts it from a table. How much power did the boy use on the backpack? ______________________________________ A child pulls a wagon, doing 360 J of work in 8.0s. How much power is exerted? _______________________________________

Lesson 2: Using Machines What is a machine? A machine is _________________________ _____________________________________ Snow shovel, scissors, watch There are simple and complex machines All machines make tasks _______but they______ ________________________________ required Machines change the way in which the work is done

Input Force to Output Force In order to use a machine, you must apply a force. __________ force- force you apply to the object Figure 6 on page 96- apply a force on the hammer The machine changes the input force into an ______ _______________ Output force is on the nail _________ force- the force the machine applies For example, the hammer changes the input force to an output force that pulls the nail out of the board

Input Work to Output Work Machines convert, or change, ______work to _______ work input work, Win = (_______force x distance the machine ___________________of the input force) The output work, Wout = (_______force x the distance the machine ___________________ of the output force) Work is done when applying a force on something and making it move

Input Work to Output Work For example: a pair of scissors IDENTIFY THE INPUT FORCE AND THE OUTPUT FORCE: You apply an _________force that moves the blades and does work You have to ________the handles to make the blades move The scissors ________________________ Output force

How do machines make work easier to do ? Three ways: It can change… __________________________________ General Rule: True for all machines You apply a _______ force over a ________ distance You apply a __________ force over a _________ distance

Change the Size of a Force A ____________ is a machine Make it easier by changing the ________ of the force from small to greater When the output force is greater than the input force, the output force _____________________________________ Example: Figure 7

Change the Distance a Force Acts Using a rake to gather leaves is an example of a machine that _______________ the distance over which a force acts. The person’s hands move the top of the rake a ____________ distance What force is person applying? ______________________ The other end sweeps through a ____________ distance What force is the rake applying? ___________________ Makes it easier to rake leaves

Continued… The force applied by the rake ____________ as the distance over the force acts (the output ___________) ____________ When the output force acts over a ________ distance than the input force, the output force is ______ than the input force.

Change the Direction of a Force Example : a pulley in Figure 7 on page 97 As the free end of the rope is pulled down, the object tied to the other end of the rope is lifted up. The machine changes the __________ of the applied force. Equal ______and _________forces act over __________ distances.

What is mechanical advantage? Most machines change the size of the force applied to them. A machine’s mechanical advantage is the _____________________________________ _______________________________________ MA = Fout / Fin Mechanical advantage = ________ force (in N) divided by ________ force (in N)

Continued… MA can be less than, equal to, or greater than 1 ______________: output force > input force Crowbar ______________: output force < input force Rake ______________: output = input Pulley

Continued… The ideal mechanical advantage (IMA) is the mechanical advantage if ____________________. Can machines operate at IMA? _______, because __________________________. Page 98: solve the practice problem

What is efficiency? The output WORK done by a machine ___________________ the input WORK of the machine because of friction. Friction converts some of the input work to _______________________. The converted energy cannot be used to do work.

Continued… The efficiency of a machine is the ratio of the output WORK to the input WORK. Efficiency (%) = output work (in J) x 100% input work (in J) Output work = Wout Input work = Win

Continued… Try practice problem on page 99! Because output work is always less than input work, a machine’s efficiency is always less than ____________________. Figure 8 on page 99 _____________a machine’s moving parts _____________ efficiency Try practice problem on page 99!

Lesson 3: Simple Machines What is a simple machine? A simple machines do work ______________________ Six types: _________________ ________________________ __________________

Levers A lever is a simple machine _______________ ______________________________________. The fixed point about which a lever pivots is called a _____________. Figure 10 (soda can) Fulcrum: finger tab attaches to the can ________and ________forces act on opposite ends of fulcrum

Levers Input arm: _________________________________ Output arm: _______________________________ There are three types of levers They differ in where the ________and ________forces are relative to the ___________

First-class Lever The _________ is in between the input and output force Direction of input and output are always _______

Second-class lever __________force is in between the input force and the fulcrum The output and input act in the ________ direction Makes the output force ___ input force Wheelbarrow Nut cracker

Third-class Lever The ________force is between the output force and the fulcrum Output and input act in the _______direction Output force _____ input force Tweezers, rake, Broom

First-class Lever The location of the fulcrum determines the MA MA of a first class lever __________ Greater than 1: input arm is _______ than the output arm Output force is ________than the input force Less than 1: input arm is ________ than the output Output force is _______ than the input force Equal to 1: input and output arms & forces are _______

Second-class Lever Output arm is _______than the input arm Output force __________input force The MA is always __________________ For all second-class levers

Third-class Lever Output arm is always ________ than the input arm Output force ___________ input force MA is always ________________ For all third-class levers

Levers in the Human Body Body uses all three classes of levers to move __________ provide the input force Neck Foot Arm Figure 12 on page 106

Neck First-class _________ : joint connecting spine and skull Neck muscles provide the _______force Output force is applied to the _______and helps support your head’s _________

Foot When standing on your toes, the foot acts as a second- class lever Ball of foot: ______ Input force: comes from the muscles on the _____________

Arm Third-class lever Elbow: _________ Input force: ________ located near the elbow (forearm muscle/ bicep)

Wheel and Axle Is an _________________________________ _______________________________________ Axle=shaft Example: screwdriver Handle- wheel because it has the _________ diameter shaft=- axle attached to the _________ _______ the handle and the shaft rotate when the handle turns

Using a Wheel and Axle When you turn the screwdriver _______force applied to the handle (wheel) _______force applied to the _______by the screwdriver’s _______ The wheel is larger than the axle= ________________________ This makes the screw easier to turn instead of using your finger

Inclined Planes Is a _______________. Also known as a _____ Takes less _______ to move an object upward along a ramp than it does to lift the object straight up Useful for moving _______________ Because of __________, no ramp operates at its ______________

Wedge A ______________________________ A type of inclined plane with one or two _______________________ Doorstop- has _________sloped side The shape of the wedge gives the _______ forces a different direction than the _______ force Example: teeth How?

Screws Is an _________________________________ _______________________________________ The screw threads change the _______force to an __________ force What’s input force? ___________________ The output force pulls the screw ___________________ Figure 16 on page 108

Pulleys A simple machine that is a ____________________ ___________________________________________

Fixed Pulleys A fixed pulley only changes the ___________ of the force Example: window blind Cord passes through the fixed pulley (of the window frame) MA= ___________________

Movable Pulleys & Pulley Systems Can be attached to the object being lifted Called a ___________________ Movable pulleys _____________the force needed to lift an object; distance the force acts over ________________ Pulley system Combination of _______and ________pulleys that work together

MA of Pulleys The MA is equal to the _______of sections of _____ pulling up on the object

Find the MA

What is a compound machine? _____________ simple machines that operate together form a compound machine Figure 18 Can opener _________ -class lever to move the handle ___________________to turn the blade ____________to puncture the lid

Gears A gear is a____________________________ _______________________________________ Two or more gears form a compound machine When they interlock, one gear causes the other to ___________ The direction of the gears ___________ Different _______= different _________

Gears Continued… Smaller gears rotate _________than larger gears Amount of _______transmitted through the gears is affected by the ________ Input force applied to a larger gear is reduced when it is applied to a smaller gear