Simple Machines

Work or Not? What is work and what is not? a teacher lecturing to her class a mouse pushing a piece of cheese with its nose across the floor

What is work? In science, the word work has a different meaning than you may be familiar with. The scientific definition of work is: using a force to move an object a distance (when both the force and the motion of the object are in the same direction.)

Work or Not? Now, according to the scientific definition, what is work and what is not? a teacher lecturing to her class a mouse pushing a piece of cheese with its nose across the floor

What ’ s work? A scientist delivers a speech to an audience of his peers. A body builder lifts 350 pounds above his head. A mother carries her baby from room to room. A father pushes a baby in a carriage. A woman carries a 20 kg grocery bag to her car?

What ’ s work? A scientist delivers a speech to an audience of his peers. No A body builder lifts 350 pounds above his head. Yes A mother carries her baby from room to room. No A father pushes a baby in a carriage. Yes A woman carries a 20 km grocery bag to her car? No

Your family is moving! You can’t leave your house without your favorite rock from your rock garden! (how would you make any friends without it to show off) You have a slight problem… how can you get the rock into the back of the truck without hurting yourself? You Your Favorite Rock (actual size) Truck

You could create a ramp or even a pulley system to help you get your prized rock in the back of the truck! You Your Favorite Rock (actual size) Truck

NSF North Mississippi GK8 Simple Machines Have few or no moving parts Make work easier Can be combined to create complex machines Six simple machines: Lever, Inclined Plane, Wheel and Axle, Screw, Wedge, Pulley Have few or no moving parts Make work easier Can be combined to create complex machines Six simple machines: Lever, Inclined Plane, Wheel and Axle, Screw, Wedge, Pulley

NSF North Mississippi GK8 Lever Has three parts to it: 1)Fulcrum 2) the load 3) the effort Trade off: must move lever large distance to move load small distance There are 3 types of levers Has three parts to it: 1)Fulcrum 2) the load 3) the effort Trade off: must move lever large distance to move load small distance There are 3 types of levers

LEVER

NSF North Mississippi GK8 1 st Class Lever The fulcrum is located between the effort and the load Direction of force always changes Examples are scissors, pliers, and crowbars The fulcrum is located between the effort and the load Direction of force always changes Examples are scissors, pliers, and crowbars

First Class Lever Fulcrum between effort and resistance.

NSF North Mississippi GK8 2 nd Class Lever The resistance is located between the fulcrum and the effort Direction of force does not change Examples include bottle openers and wheelbarrows The resistance is located between the fulcrum and the effort Direction of force does not change Examples include bottle openers and wheelbarrows

Resistance between fulcrum and effort. Second Class Lever

NSF North Mississippi GK8 3 rd Class Lever The effort is located between the fulcrum and the resistance Direction of force does not change, but a gain in speed always happens Examples include ice tongs, tweezers, hammers, and shovels The effort is located between the fulcrum and the resistance Direction of force does not change, but a gain in speed always happens Examples include ice tongs, tweezers, hammers, and shovels

Effort between resistance and fulcrum. Third Class Lever

Input and Output Forces When you use a machine to do work, you exert a force over some distance. For example, you exert a force on the shovel when you use it to lift soil. The force you exert on the machine is called the input force. The machine does work by exerting a force over another distance, called the output distance.

NSF North Mississippi GK8 Mechanical Advantage To do these tasks without a machine would be difficult. We know that a machine multiplies whatever force put into it (so you can complete the task) : - Using a screwdriver to turn a screw - Twisting a nail with pliers - Carrying a box up a ramp instead of stairs The amount that the machine multiplies that force is the mechanical advantage of the machine Abbreviated MA To do these tasks without a machine would be difficult. We know that a machine multiplies whatever force put into it (so you can complete the task) : - Using a screwdriver to turn a screw - Twisting a nail with pliers - Carrying a box up a ramp instead of stairs The amount that the machine multiplies that force is the mechanical advantage of the machine Abbreviated MA

NSF North Mississippi GK8 Mechanical Advantage: Lever What is the MA for the example? Distance from effort to fulcrum: 10 feet Distance from load to fulcrum: 5 feet The answer is: MA = 10/5 = 2

NSF North Mississippi GK8 Inclined Planes A slope or ramp that goes from a lower to higher level Makes work easier by taking less force to lift something a certain distance Trade off: the distance the load must be moved would be greater than simply lifting it straight up A slope or ramp that goes from a lower to higher level Makes work easier by taking less force to lift something a certain distance Trade off: the distance the load must be moved would be greater than simply lifting it straight up

INCLINED PLANE

NSF North Mississippi GK8 Mechanical Advantage: Inclined Plane The mechanical advantage of an inclined plane is the length of the slope divided by the height of the plane, if effort is applied parallel to the slope Let’s say S = 15 feet, H = 3 feet The mechanical advantage of an inclined plane is the length of the slope divided by the height of the plane, if effort is applied parallel to the slope Let’s say S = 15 feet, H = 3 feet So for our plane MA = 15 feet/3 feet = 5

NSF North Mississippi GK8 Wheel and Axle A larger circular wheel affixed to a smaller rigid rod at its center Used to translate force across horizontal distances (like a car) Trade off: the wheel must be rotated through a greater distance than the axle A larger circular wheel affixed to a smaller rigid rod at its center Used to translate force across horizontal distances (like a car) Trade off: the wheel must be rotated through a greater distance than the axle

WHEEL AND AXLE

NSF North Mississippi GK8 Mechanical Advantage: Wheel and Axle So for our wheel and axle MA = 10”/2” = 5

NSF North Mississippi GK8 Screw An inclined plane wrapped around a rod or cylinder Used to lift materials or bind things together An inclined plane wrapped around a rod or cylinder Used to lift materials or bind things together

SCREW

NSF North Mississippi GK8 Mechanical Advantage: Screw So for our screwdriver MA = 3.14”/0.1” = 31.4 So for our screwdriver MA = 3.14”/0.1” = 31.4 Circumference = ∏ x 1” = 3.14” Pitch = 1/10” = 0.1”

NSF North Mississippi GK8 Wedge An inclined plane on its side Used to cut or force material apart Often used to split lumber, hold cars in place, or hold materials together (nails) An inclined plane on its side Used to cut or force material apart Often used to split lumber, hold cars in place, or hold materials together (nails)

WEDGE

NSF North Mississippi GK8 Mechanical Advantage: Wedge So for our wedge, MA = 6”/2” = 3 They are one of the least efficient simple machines So for our wedge, MA = 6”/2” = 3 They are one of the least efficient simple machines

NSF North Mississippi GK8 Pulley A rope or chain free to turn around a suspended wheel By pulling down on the rope, a load can be lifted with less force Trade off: no real trade off here; the secret is that the pulley lets you work with gravity so you add the force of your own weight to the rope A rope or chain free to turn around a suspended wheel By pulling down on the rope, a load can be lifted with less force Trade off: no real trade off here; the secret is that the pulley lets you work with gravity so you add the force of your own weight to the rope

NSF North Mississippi GK8 Mechanical Advantage: Pulley The Mechanical Advantage of a pulley is equal to the number of ropes supporting the pulley So for the pulley system shown there are 3 ropes supporting the bottom pulley MA = 3 This means that if you pull with a force of 20 pounds you will lift an object weighing 60 pounds The Mechanical Advantage of a pulley is equal to the number of ropes supporting the pulley So for the pulley system shown there are 3 ropes supporting the bottom pulley MA = 3 This means that if you pull with a force of 20 pounds you will lift an object weighing 60 pounds

NSF North Mississippi GK8 The trick is WORK Simple machines change the amount of force needed, but they do not change the amount of work done What is work? Work equals force times distance W = F x d By increasing the distance, you can decrease the force and still do the same amount of work Simple machines change the amount of force needed, but they do not change the amount of work done What is work? Work equals force times distance W = F x d By increasing the distance, you can decrease the force and still do the same amount of work

NSF North Mississippi GK8 Eduardo is helping his family move out of their old house. Help him decide which task would be easier, and then help him figure out what simple machine makes the job easier.

NSF North Mississippi GK8 Eduardo has to move some heavy boxes into the moving truck. AB He would use an Inclined Plane

NSF North Mississippi GK8 Eduardo has to move a heavy box a long distance. AB He would use a cart with wheels and axles.

NSF North Mississippi GK8 Eduardo needs to tear off a piece of packing tape. AB He would use a scissors or wedges.

NSF North Mississippi GK8 Eduardo needs to move a heavy box to his room on the fourth floor. AB He would use a pulley

NSF North Mississippi GK8 Eduardo needs to help his father move the refrigerator. He would use a lever BA

NSF North Mississippi GK8 Eduardo needs to help his father change a flat tire on the moving truck. AB He would use a jack that uses a screw.

Rube Goldberg Machines Rube Goldberg machines are examples of complex machines. All complex machines are made up of combinations of simple machines. Rube Goldberg machines are usually a complicated combination of simple machines to accomplish a simple task. By studying the components of Rube Goldberg machines, we learn more about simple machines

When you slip on ice, your foot kicks paddle (A), lowering finger (B), snapping turtle (C) extends neck to bite finger, opening ice tongs (D) and dropping pillow (E), thus allowing you to fall on something soft. Safety Device for Walking on Icy Pavements

NSF North Mississippi GK8 Sources COSI.org Simple Machines. Accessed 3 February Jones, Larry. January Science by Jones: Levers. Accessed 2 February Mikids.com Simple Machines. Accessed 2 February Professor Beaker’s Learning Labs. August Simple Machines: inclined planes. Accessed 2 February Wikepedia. Accessed 3 February

NSF North Mississippi GK8 Image Sources resources/simple-machines/flag-pole.jpg resources/simple-machines/flag-pole.jpg

NSF North Mississippi GK8 Images Sources (cont.)