Simple Machines

1. Simple Machines ESCI 215 Chapter 10

2. Early Inventions “Necessity is the mother of invention” (Friedl & Koontz, 2005, p.179) • Early humans in all cultures invented tools to make a possible or easier • To move a boulder, dig a hole, catch a fish • Often made of wood, bone or stone and then metal • Still required muscle power from humans and animals • These tools are examples of simple machines

3. Machines Make Work Easier • Machine – something that makes a job easier by changing one or more of the following: • Direction of force • Amount or size of force needed • Speed or distance of force • Simple machine – mechanical machine that convert one kind of motion into another • Pull down on a flag pole rope and the flag goes up • Pedal a bike with your feet in circles and the bike goes forward

4. Simple Machines • 6 categories: • Simple machines are related to each other and these 6 categories can be regrouped to show the relationships: • Levers: levers, wheel and axle, pulley • Inclined plane: inclined plane, screw, wedge

5. Compound Machines • Compound machine – more than one simple machine combined to create a more complex machine • 2000 years ago, a Greek scientist, Archimedes, invented the Archimedean screw (now called an auger) • He pumped water uphill, by combining a screw, inclined plane, lever, and wheel and axle • See figure 10.1 in text on page 180

6. Force • Force – a push or pull • Force is needed to make a machine work • Usually measured in pounds and Newtons Force = mass x acceleration F = ma • Gravity – a type of acceleration that pulls objects toward the earth • Gravity causes objects to exert a force • When you stand your body weight pushes on the ground • “Put your weight into it” • Mass and weight are not the same • weight is a force, but mass is not

7. Work • Work usually involves exerting 1 force against another (i.e. a push or pull against gravity or friction) • 2 factors affect work: • Force applied • Distance the force is applied over • Amount of work is the same for the following: • Pull a wagon of dirt for 2 km • Pull a wagon of dirt 2 times as hard for 1 km • Work – the amount of force or weight (mass x gravity) applied over a distance W = f x d W = mass x gravity x distance

8. Work with Machines • Machines can increase the force of your effort, making work easier • But, you have to apply the force over a longer distance • Actual mechanical advantage (AMA) – a measure of how much a machine can increase our force AMA = resistance force = fr effort force fe Ex: A screwdriver handle travels farther than the tip when you push down. If it travels 3x farther, it will be 3x easier to open than by hand

9. Levers • Lever - A tool that pivots on a point to change the direction and the force of a movement • Fulcrum – the point where a lever pivots • Levers are used to change the amount, strength and direction of movement • The force used to move a lever is called the effort force • The amount of force the lever applies on the opposite side is called the resistance force (also called load) • The position of the force and the load can be changed by moving them to different points on the lever • The closer the object is to the fulcrum, the easier it is to move We = Wr Work done on effort side = work done on resistance side • As the resistance force increases, the distance on the effort side must increase (an inverse relationship)

10. Levers • Event 10-A Uplifting Students shows how students can use a lever to make it easy to lift each other up • Using a broom handle to apply the effort force and a chair back as the fulcrum, a student laying on a desk can be lifted • Increasing the distance between the effort force and fulcrum, decreases the effort needed to lift the student

11. Levers • Event 10-B Balancing your Budget shows the inverse relationship of effort force and resistance force • The longer the distance between the pivot point and the penny, the more pennies can be lifted on the other side • 1 penny 20cm from fulcrum = 4 pennies 5cm from fulcrum • See Fig 10.4 on page 183 • Event 10-C Balancing Mobile Act is an online game

12. Levers • Not all levers work the same • The fulcrum is not always between the effort and resistance forces • Students should: • know that there are 3 different types of levers • know that each type has a different arrangement of effort, load and fulcrum • Be able to identify where the load, effort and fulcrum are on common simple machines

13. Levers Scissors, seesaws, rowboat oars, crowbar There are 3 types or classes of levers: Nutcracker, wheelbarrow, bottle opener, stapler, 3-hole paper punch Tweezers, elbow, baseball bat, fishing pole, fly swatter

14. Pulleys • Pulley – a wheel with a groove in its rim where rope is placed • Wheel is attached to a high surface • One end of the rope is tied to an object; the other end goes over the wheel and pulled down to lift the object • Pulleys make it easier to lift a heavy load by giving a mechanical advantage • There are different types of pulleys: • Fixed • Movable • Combined

15. Fixed Pulley: • Wheel attached to surface • Changes the direction of the applied force • You pull down and force pulls up on object • NO mechanical advantage – same amount of force is required

16. Movable Pulley: • Pulley moves along the rope • Wheel supports the load • Effort is in the same direction as movement • Reduces the forces needed to move an object

17. In the second picture, the weight is held by two ropes instead of one. That means the weight is split equally between the two ropes, so each one holds only half the weight. http://www.swe.org/iac/LP/pulley_03.html

18. Combined (double) Pulley: • Has at least two wheels • The more complex the pulley, the less effort required to move the object

19. The more lines of support (ropes) a pulley has, the more mechanical advantage it has! http://www.swe.org/iac/LP/pulley_03.html

20. Pulleys • Event 10-E Changing Directions shows how a single fixed pulley changes the direction of motion • Lifting heavy objects is made easier because it is easier to pull down than to lift up • Gravity is working with you when you pull down • There is no mechanical advantage • Event 10-F Pulley Play shows how a moveable pulley moves with the rope and keeps the effort force and load moving in the same direction • You pull 2x as far, but the load feels ½ as heavy • The further the effort force moves (distance), the less force needed to lift something W = f x d

21. Block and Tackle • Combining a fixed pulley and a moveable pulley • Change in direction of motion – from fixed pulley • Gain in effort force – from moveable pulley • The more wheels, the easier it is to lift the load • Weight is spread over more rope • Distance rope is pulled increases with every wheel added • Frequently used in construction equipment • Cranes and hoists

22. Wheel and Axle Wheel and axle – a wheel connected to a rigid pole and they both turn together • Outer rim of wheel has a larger diameter so it moves a greater distance with small effort and inner axle moves short distance producing a large force • Steering wheel of a car is turned a lot compared to how much the wheels(axle) turn • Less effort is needed to turn the steering wheel because the distance of effort force is longer (length of axle) • Large faucet handle makes it easier to turn tap off • It is a modified lever • The center of the axle acts as a fulcrum – making the wheel a lever that rotates around in a circle

24. Gears • Gears – wheels with teeth that fit together to turn each other • Help change direction, speed, or force of movement • Event 10-G Putting Teeth into your Wheels has students classify objects according to whether they are a wheel and axle or not. Then they sub-classify the wheel and axle category to gears and non gears. • Event 10-H Mean Clean Bubble-Making Machine shows how gears change the direction and speed of movement • Egg beater is a wheel and axle (gears) • Turn handle - turns the large gear - turns the smaller gears – rotates beaters faster – more bubbles quicker • Wooden spoon is a 3rd class lever • Large surface area of spoon – takes more effort to move it in water

25. Event 10-I Gears are Wheels Too shows the advantages of gears in a bicycle • Bike wheels turn at different speeds and with different amounts of effort compared to bike pedals • Gears decrease the force needed to pedal by increasing the distance you pedal

26. Inclined Plane • Inclined plane – a slope (ie. Ramp, mountain, stairs) that can make it easier to move objects • The steeper the slope, the harder it is to climb • The longer the incline – the further you travel – the less force needed for same amount of work W = f x d

27. Inclined Plane • Event 10-J Eggactly Why do we use a Ramp? Shows how inclined planes can make it easier to lift or lower heavy objects by using less force • Using a ramp, increases the distance over which the egg is lowered – decreases the force it hits the ground with • Event 10-K Uphill Tractor Pull shows how changing the incline of a slope, changes the amount of effort needed to lift an object

28. Wedge • Wedge – an object used to split or separate things; made of 2 or more inclined planes or has a conical shape (i.e. ice cream cone shape) • Changes the forward motion into a sideways motion • It is a moving inclined plane • Event 10-L Fruit and Vegetable Challenge has students make faces out of vegetables • Students discover that vegetables cut into wedges, slice into the “heads” easier than round pieces • Wedges can separate things with less effort by increasing the distance that the force is applied over

29. Wedge • Event 10-M How “Aboat” that Machine shows a compound machine • Students build a paddle boat and investigate how a wheel and axle and wedge work to move the boat forward

30. Screw • Screw – an inclined plane wrapped around a central point and a wedge with a pointed tip • Screwjack is used to lift a car • Turning the jack handle moves the force along a long distance in order to lift the car a short distance

31. Screw • Event 10-N Hardwood or Softwood shows how the incline and wedge properties of a screw make it easier to insert into an object • Students compare the effort required to push a screw into wood versus rotating it into wood • Event 10-O Screwy Pump shows how an Archimedean screw (auger) can be used to make water flow uphill

32. Assessment and Instruction • Assessment for Grades 3 – 5 • www.edheads.org/activities/simple-machines/index.shtml • Students identify simple machine on this animated site • Can be used as a review before a test OR • Students make a model of a simple machine (i.e. pulley to raise a miniature flag) • Evaluation: • Paragraph describing how the machine works • Design features: neatness, durability, does it move freely, etc. • Labeled parts, including effort force, load, fulcrum • List of everyday uses

33. Websites • www.edheads.org/activities/simple-machines/index.shtml • www.enchantedlearning.com/physics/machines/Levers.shtml • www/smartown.com/sp2000/machines2000/main.htm • www.beakman.com/lever/lever.html • www.mos.org/sln/Leonardo/InventorsToolbox.html

34. Discussion • Where does this topic fit into the Science curriculum? • Which grades and strands? • Which curriculum objectives relate to the discrepant events?