Simple Machines Simple Machines Matt Aufman and Steve Case University of Mississippi NSF NMGK-8 February 2006 Matt Aufman and Steve Case University of Mississippi NSF NMGK-8 February 2006

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 A rigid board or rod combined with a fulcrum and effort By varying position of load and fulcrum, load can be lifted or moved with less force Trade off: must move lever large distance to move load small distance There are 3 types of levers A rigid board or rod combined with a fulcrum and effort By varying position of load and fulcrum, load can be lifted or moved with less force Trade off: must move lever large distance to move load small distance There are 3 types of levers

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

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

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 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 and shovels

NSF North Mississippi GK8 Mechanical Advantage We know that a machine multiplies whatever force you put into it: - 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 We know that a machine multiplies whatever force you put into it: - 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 (IMA) Ideal MA: This is the MA of a machine in a world with no friction, and no force is lost anywhere (AMA) Actual MA: This is simply the MA of a machine in the world as we know it - Force is lost due to friction - Force is lost due to wind, etc. Can we have an ideal machine? (IMA) Ideal MA: This is the MA of a machine in a world with no friction, and no force is lost anywhere (AMA) Actual MA: This is simply the MA of a machine in the world as we know it - Force is lost due to friction - Force is lost due to wind, etc. Can we have an ideal machine?

NSF North Mississippi GK8 Mechanical Advantage: Lever The mechanical advantage of a lever is the distance from the effort to the fulcrum divided by the distance from the fulcrum to the load For our example, MA = 10/5 = 2 The mechanical advantage of a lever is the distance from the effort to the fulcrum divided by the distance from the fulcrum to the load For our example, MA = 10/5 = 2 Distance from effort to fulcrum: 10 feet Distance from load to fulcrum: 5 feet

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

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 So for our plane MA = 15 feet/3 feet = 5 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 So for our plane MA = 15 feet/3 feet = 5 Let’s say S = 15 feet, H = 3 feet

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 (wheels on a wagon) or to make rotations easier (a doorknob) 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 (wheels on a wagon) or to make rotations easier (a doorknob) Trade off: the wheel must be rotated through a greater distance than the axle

NSF North Mississippi GK8 Mechanical Advantage: Wheel and Axle The mechanical advantage of a wheel and axle system is the radius of the wheel divided by the radius of the axle So for our wheel and axle MA = 10”/2” = 5 The mechanical advantage of a wheel and axle system is the radius of the wheel divided by the radius of the 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

NSF North Mississippi GK8 Mechanical Advantage: Screw The Mechanical advantage of a screw is the circumference of the screwdriver divided by the pitch of the screw The pitch of the screw is the number of threads per inch So for our screwdriver MA = 3.14”/0.1” = 31.4 The Mechanical advantage of a screw is the circumference of the screwdriver divided by the pitch of the screw The pitch of the screw is the number of threads per inch 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)

NSF North Mississippi GK8 Mechanical Advantage: Wedge Much like the inclined plane, the mechanical advantage of a wedge is the length of the slope divided by the width of the widest end So for our wedge, MA = 6”/2” = 3 They are one of the least efficient simple machines Much like the inclined plane, the mechanical advantage of a wedge is the length of the slope divided by the width of the widest end 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 Examples: Lever: Work is equal on both sides of a lever. You move the long end a LARGE distance with SMALL force. The other end moves a SMALL distance with a LARGE force, which is why it can lift heavy objects. Lever: Work is equal on both sides of a lever. You move the long end a LARGE distance with SMALL force. The other end moves a SMALL distance with a LARGE force, which is why it can lift heavy objects. Inclined Plane: It takes a certain amount of work to get the cabinet into the truck. You can either exert a LARGE force to lift it the SMALL distance into the truck, or you can exert a SMALL force to move it a LARGE distance along the ramp.

NSF North Mississippi GK8 Efficiency The efficiency is a ratio that measures how much work the machine produces versus how much work goes in Example: We have an inclined plane with an ideal MA of 3. We measure our real-life inclined plane and find an MA of 2. Efficiency = Actual MA/Ideal MA x 100% = (2/3) X 100% = 66.66% The efficiency is a ratio that measures how much work the machine produces versus how much work goes in Example: We have an inclined plane with an ideal MA of 3. We measure our real-life inclined plane and find an MA of 2. Efficiency = Actual MA/Ideal MA x 100% = (2/3) X 100% = 66.66%

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