A Study of Simple Machines

A Study of Simple Machines Today you will do a traveling tour to learn about the types of simple machines and how they affect work. At each stop on the tour, read the directions carefully and complete the requirements. ***Note: There will be a stations quiz following the activity*** Henderson, 2002-2003 Tour stop #1: WORK WORK: You are doing work when you use a force to cause motion. To measure the amount of work you do, multiply the force times the distance the object moved. • • • Motion is the changing of position of an object in reference to a starting point frame of reference). Work is the transfer of energy through motion. In order for work to take place, a force must be exerted through a distance. Work= F x D (work= force x distance the object moved) • • • • • • Force (or weight) is measured in newtons. Distance is measured in meters. Unit measure of work = newton x meter or Newton-meter Work is measured Joules (N-m) after British Scientist James Prescott Joule. A newton meter (N-m) is called a joule (J). One Joule = N-m, is work done when a force of one newton acts through a distance of one meter. Amount of Work (w) done depends on two things: A. The amount of Force (F) exerted. (Something has to move.) B. The Distance (d) over which the Force is applied. (The motion must be in the direction of the applied force. Machines make work easier. The work that comes out of a machine can never be greater than the work put into a machine. We have defined work to be the force used multiplied by the distance an object moves. Can we lift a ten pound object with just five pounds of force? The answer is yes if we use a simple machine to help. When we think of a machine we most often think of an electric device such as a clothes washer or a dish washer. Not all machines are electric. • The amount of work a machine produces equals the force used multiplied by the distance the machine lifts or moves and object. • How does a simple machine make work easier? A. Transferring the force from one place to another. B. Changing the direction of a force C. Increasing the magnitude of a force D. Increasing the distance or speed of a force • What do you need to do work? Energy! Energy is the ability to do work. Henderson, 2002-2003 Calculating work: Problem: Which takes more work? Moving object #1 from A to B, moving object #2 from A to B, or holding object #3 the same distance as A to B, but above the floor? 1. Study the three objects. 2. Make a hypothesis about which task will require more work. 3. Experiment to determine the amount of work required in each scenario. Record and label your work for each scenario. Make sure you indicate the proper units! Questions: 1. How did the amount of work compare for each scenario? Why? Henderson, 2002-2003 Tour stop #2: FORCE • A Force is a PUSH or a PULL, that causes a change in the motion or shape of an object. Examples: Pushing open a door, shoving a book across a desk, or the pull of gravity on a ball when you drop it. Words to think about that use force – pushing, pulling, stretching, squeezing, bending, and falling. Forces can be equal (balanced forces): holding a book up in your palm of your hand, or a book laying on the table - your hand or the table pushes up and the book pushes down. Whenever an object is caused to move, whether from a standstill or while already in motion, a force is required. Gravity is a universal force. Gravitational force causes every object to attract every other object (ball falls to the ground, the moon orbiting the Earth). Every object in the universe exerts a force on every other object, and that force is gravity. Friction is a force that opposes motion. Friction occurs when two substances rub together. Rub your hands together, what did you feel? Why? Heat is a byproduct of friction. The motion of objects is reduced because of friction (it’s why you stop swinging on a swing, why a ball stops rolling). Friction can be reduced by smoothing and polishing the surface of contact, by lubricating surfaces with grease or oil, or by using rollers instead of sliding. Sometimes we want to increase frictional forces – Example: when using the brakes on a bike or car, we are increasing friction in order to stop. If there were no friction, your life would be much different. You wouldn't be able to walk (think about walking on ice) or hold things between your fingers. You wouldn't be able to turn the pages of a book, or keep your shoes tied, or stop your car with the brakes. What do you call the force of gravity on your mass? WEIGHT! Remember? Two important factors dealing with force are: Mass and Distance, The Earth holds you because its mass is so large compared to yours, but you do not feel the gravity pull of your neighbor sitting next to you! Force in the SI is measured in Newton and is part of the equation for Work! W = F x d. F = mass x acceleration Acceleration on Earth due to the force of gravity is 9.8 m/s/s • • • • • • • • • • • • • • • Henderson, 2002-2003 Diagramming force: Directions: For each situation below, make a sketch to show the forces represented. After you try each one, check your answer and make the necessary corrections. After a few tries, you should have it mastered! Do as many as possible before you are instructed to rotate. 1. A book is at rest on a table top. Diagram the forces acting on the book. 2. A girl is suspended motionless from a bar which hangs from the ceiling by two ropes. Diagram the forces acting on the girl. 3. An egg is free-falling from a nest in a tree. Neglect air resistance. Diagram the forces acting on the egg as it falls. 4. A flying squirrel is gliding (no wing flaps) from a tree to the ground at constant velocity. Consider air resistance. Diagram the forces acting on the squirrel. Henderson, 2002-2003 5. A rightward force is applied to a book in order to move it across a desk with a rightward acceleration. Consider frictional forces. Neglect air resistance. Diagram the forces acting on the book. 6. A rightward force is applied to a book in order to move it across a desk at constant velocity. Consider frictional forces. Neglect air resistance. Diagram the forces acting on the book. 7. A middle school student rests a backpack upon his shoulder. The pack is suspended motionless by one strap from one shoulder. Diagram the vertical forces acting on the backpack. 8. A skydiver is descending with a constant velocity. Consider air resistance. Diagram the forces acting upon the skydiver. Henderson, 2002-2003 9. A force is applied to the right to drag a sled across loosely-packed snow with a rightward acceleration. Diagram the forces acting upon the sled. 10. A football is moving upwards towards its peak after having been booted by the punter. Neglect air resistance. Diagram the forces acting upon the football as it rises upward towards its peak. 11. A car is coasting to the right and slowing down. Diagram the forces acting upon the car. Henderson, 2002-2003 Tour stop #3: LEVER The lever is a simple machine made with a bar free to move about a fixed point called a fulcrum. • • • One of the earliest and simplest of machines, a large stick would work as a lever to move huge rocks. The lever is essentially a rigid bar that is free to turn about a fixed point called the fulcrum. Every Lever has three (3) parts: A. Resistance Force or Load, What you are trying to move or lift. B. Effort Force - The Work done on the lever. C. Fulcrum – A fixed pivot point. There are three types of levers. A first class lever is like a teeter-totter or see-saw. One end will lift an object (child) up just as far as the other end is pushed down. A second class lever is like a wheel barrow. The long handles of a wheel barrow are really the long arms of a lever. A third class lever is like a fishing pole. When the pole is given a tug, one end stays still but the other end flips in the air catching the fish. ACTIVITY #1 Find other examples of levers from the materials on the table. Try to find one of each class. Draw each below, labeling its class. Henderson, 2002-2003 ACTIVITY #2: What happens when the distance is changed between the fulcrum and the effort force? ***Note: You will construct a data chart to record your findings*** MATERIALS: mass object Procedure: 1. Place the fulcrum under the 50 cm mark of the meter stick. Situate the lever so that meter stick fulcrum spring balance the 100 cm mark is hanging over the edge of the table. 2. Place the object on top of the meter stick at any given mark. 3. Pull down on the spring balance which is attached to the end of the meter stick (which should be hanging over the edge of the table).This is the effort force. 4. Record the distance (the mark on which you put the object) and the force necessary to do this. 5. Move the object on top of the meter stick to another mark. 6. Pull down on the spring balance which is attached to the end of the meter stick (which should be hanging over the edge of the table).This is the effort force. 7. Record the distance (the mark on which you put the object) and the force necessary to do this. 8. Compare your effort force in steps 4 and 7. 9. Move the fulcrum to the 20 cm mark repeat steps 2-8. 10.Construct a data table in the space below to record your findings. Questions: 1. What class lever is this? 2. Write a paragraph to compare the effect of the fulcrum position on the force required to move a load Henderson, 2002-2003 Tour stop #4: PULLEY A pulley is a simple machine made with a rope, belt or chain wrapped around a grooved wheel. A pulley works two ways. It can change the direction of a force or it can change the amount of force. A fixed pulley changes the direction of the applied force. (Ex. raising the flag ) . A movable pulley is attached to the object you are moving. A pulley is a grooved wheel that turns around an axle (fulcrum), and a rope or a chain is used in the groove to lift heavy objects. • A pulley changes the direction of the force – instead of lifting up, you can pull down using your body weigh against the resistance (load, what you are lifting). • A pulley may be fixed, moveable, or used in combination. • The simple pulley gains nothing in force, distance or speed, but it changes the direction of the force. (Ex: hoisting a sail) Samples of Pulleys in use – raising and lowering the flag, hoisting a sail, opening curtains or mini blinds, lifting hay into a hayloft. • • Activity: 1. Sketch a diagram for each of the set-ups at this station. (Use separate paper) 2. Attach the mass to each pulley, one at a time, and record the force needed to move the object. 3. Label the amount of force on each diagram. 4. Label, with arrows, the direction of your force and the direction the object moved. 5. Design a pulley set-up that will reduce the force even greater than the least amount of force already recorded. 6. Draw your set-up, indicate the amount of force, and label (with arrows) the direction of your force, and the direction the object moved. If you are not successful at this challenge, sketch at least one set-up that you tried and label it properly (according to procedure #6). ACTIVITY: Find two other examples of pulleys from the materials on the table. List them below: Henderson, 2002-2003 Tour stop #5: INCLINED PLANE An inclined plane is a simple machine with no moving parts. It is simply a straight slanted surface. (Ex. a ramp.) An inclined plane is a simple machine that makes it easier to move a heavy object to a higher elevation. It reduces the amount of force needed to lift the object. A screw is an inclined plane wrapped around a cylinder. An inclined plane is also a wedge cut in half. The Egyptians used inclined planes to build the pyramids. • • • • An INCLINED PLANE is a sloping surface used to lift heavy loads with relative little effort. The inclined plane does not move. An inclined plane provides for less effort, but not less work. The trade off is a greater distance to travel. Allows you to lift a weight you normally couldn't lift. Samples of inclined planes – escalator, stairs, ship plank, and ladder. LIFTING The force needed is equal to the weight of the barrel multiplied by the height of the platform. F = mass x height of ramp Ex: 100 lb. barrel up 5 meters = 100 lb x 5 m = 500 N. Henderson, 2002-2003 ROLLING The force equals the weight of the barrel multiplied by the height of the platform, divided by the length of the ramp. Force = mass x height of ramp / length of ramp Ex: 100 lb x 5 m / 10m = 50 N. ACTIVITY: What happens to the amount of work needed to move an object (resistance) when the distance of the inclined plane increases? Materials: spring scale weight ruler (1ft) two ramps Procedure: 1. Measure the length of each ramp (meters). Record: #1 ______________meters #2 ________________ meters 2. Attach the spring scale to the weight. 3. Slowly move the weight up the first inclined plane to rest on the top of the ramp. Move the object (resistance) at a steady rate. 4. Read the spring scale as you move the weight. 5. Record the force (newtons). Record: #1 _____________ newtons #2 _______________ newtons 6. Repeat steps 2 – 5 for the second inclined plane. 7. Write a sentence to compare the force required to pull the weight up the two inclined planes. Henderson, 2002-2003 Why is there a difference in the amount of force required to move the object the same height? 8. Calculate the amount of work required to move each object to the top of the inclined planes. Show all of your work and the proper units. Inclined plane #1 Inclined plane #2 Why isn’t there a difference in the amount of work required to move the object the same height? ***Note: If you did calculate a significant difference, you better check your work*** Activity: Look through the materials on the table. Identify three examples of inclined planes in use. List them below: Henderson, 2002-2003 Tour stop #6: WHEEL AND AXLE A wheel and axle is a modification of a pulley. A wheel is fixed to a shaft. The wheel and shaft must move together to be a simple machine. Sometimes the wheel has a crank or handle on it. Examples of wheel and axles include roller skates and doorknobs. A machine is a device that makes things easier by changing force and distance or by changing the direction of the force. A wheel and axle is a simple machine made up of two circular objects of different sizes. The wheel is the larger object. It turns about a smaller object called an axle. Because the wheel is larger than the axle, it always moves through a greater distance than the axle. A force applied to the wheel is multiplied when it is transferred to the axle, which travels a shorter distance than the wheel. Remember, work must remain the same. • • • • • • • The wheel and axle is one of the most common simple machines. It decreases the amount of force necessary to do work by increasing the distance. The wheel and axle was first used around 3000 B.C. and is one of the most important inventions in history. Rollers (several logs placed under a heavy object) were the forerunner to the wheel. The wheel and axle is basically a modified lever; the center of the axle serves as a fulcrum making the wheel a lever that rotates around in a circle. Effort force is applied to a large wheel to turn a smaller axle. Samples of the wheel and axle - door knobs, screwdrivers (the whole screwdriver), water faucets, handle bars on a bike, airplane propellers, helicopter blades, fan blades, wheels on a car, wagon wheels o Gears are a modified or special wheel and axle. o A gear is a wheel with teeth along its circumference. o Effort is exerted on one of the gears, causing the other gear to turn. o Samples of gears – bike sprockets, can opener, gears in any machine. Axle Wheel Henderson, 2002-2003 ACTIVITY: How does the simple machine called the wheel and axle make work easier? MATERIALS: empty spool of thread string paper cup 20 pennies 2 pencils tape Procedure: 1. Identify spool A and spool B on the pencil set-up. 2. Tape the string of cup A to the A spool and wind all of the string onto the spool by turning the spool away from you. Keep the string wound on the right hand side of the spool. 3. Tape the string of cup B to the B spool and wind all of the string onto the spool by turning the spool toward you. Keep the string wound on the left side of the spool. Cup A should now be down near the ground. 4. Place 10 pennies into cup A. 5. Place one penny at a time into cup B until the cup starts to move down. Observe how many pennies it took to start the movement. Compare the distance cup A moved to the distance cup B moved? 6. Now take the A string off of the spool and remove the spool from the pencil setup. 7. Tape cup A string to the pencil (instead of the spool as before) and wind it up by turning it away from you. 8. Turn the pencil toward you to wind up all of the B string onto the spool. 9. Place 10 pennies in cup A. 10. Cup B should be at its top position. Add pennies to cup B one at a time until it starts to move slowly. 11. Observe the distance both cups moved. Henderson, 2002-2003 Questions: 1. Explain the differences when comparing cup A being taped to the spool (wheel) to cup A being taped to the pencil (axle). 2. What does this prove about the advantage of a wheel and axle? Activity: Look through the materials on the table. Find three examples of the wheel and axle. List them! Henderson, 2002-2003 Tour stop #7: Energy • • • • • • ENERGY is the ability to do WORK – to cause something to MOVE. ENERGY is the ability to cause CHANGE. Energy can be found in several forms, CHEMICAL and MECHANICAL. Living things cannot work without energy and machines cannot work without energy. You cannot get more work out of a machine than the ENERGY you put into it. Due to FRICTION, the WORK produced is usually less than the energy used. ENERGY can be transferred from one form to another, but energy cannot be created or destroyed. Forms of energy include: Solar, Electrical, Heat, Light, Chemical, Mechanical, Wind, Water, Muscles, and Nuclear. All energy originates from our SUN, our number one source of energy. There are TWO types of energy: a. Potential Energy - Energy of position or stored energy. • Anything may have stored energy that gives it the potential to cause change if certain conditions are met. o Potential energy due to height above the Earth's surface is called gravitational potential energy. o Potential energy is changed to kinetic energy upon movement. • The amount of potential energy a sample of matter has depends on its position or condition. o The greater the height, the greater the potential energy. A flowerpot sitting on the ledge two stories up has potential energy because it could fall (due to gravity). Springs in toys are another example of potential energy. b. Kinetic Energy - Energy of motion. • The Greater the MASS of a moving object, the more kinetic energy it has. • Mechanical energy is the total amount of kinetic and potential energy in a system. • • Energy is always conserved. This is the Law of Conservation of Energy. Energy may change from one form to another, but it cannot be created or destroyed. • • • Activity: Look at the pictures at the table and complete the chart on the following pages. Henderson, 2002-2003 Potential Energy (yes or no) How is the potential energy stored? What opposing force is overcome? How is the potential energy put to work? (kinetic energy) by unwinding the rubberband thus propelling the boat forward A yes winding the rubberband of the paddlewheel the elasticity of the rubberband B C D E F G Henderson, 2002-2003 Potential Energy (yes or no) How is the potential energy stored? What opposing force is overcome? How is the potential energy put to work? (kinetic energy) H I J K L M N O Henderson, 2002-2003 ☺ Enrichment Simple Machine Madness (This is the enrichment opportunity for you if you love building things. Yes, groups are allowed – ask!) For more information see - http://www.rube-goldberg.com/ Have you ever seen or made a Rube Goldberg Machine? These machines rely on cause and effect. One action happens which causes another action to happen, which causes another action, which causes another action, so on and so on until its task is completed. Note: Rube Goldberg Machines are complex machines. These machines also rely on simple machines. Simple machines (lever, pulley, inclined plane, and wheel and axle) are the basis for all complex machines. Rube Goldberg Machines can be used to do just about anything. You can make one to crack an egg into a pan, wake you up with a splash of water, turn on the television, pour your pet’s food into the bowl, put toothpaste on a toothbrush, ring a bell, or do any task that you can think up. You may ask, “Why should we make these simple everyday tasks so complicated?” Why? Because they’re fun and challenging! A screw and a wedge are variations of an inclined plane. Objective: Design and produce a Rube Goldberg Machine that performs an everyday task. ▪Your machine must include at least one each of the four basic simple machines. ▪You must label each simple machine each time it is used. ▪Your machine must complete the task you assign it to do. ▪You must supply the materials for your machine (although, your teacher may be able to help you – ask!) and build your device on your own time. Points: The total possible points for this enrichment is up to 20 points added to any task. ▪One of each four simple machines = 4 points ▪ A second one of each = 4 points ▪ A third one of each = 4 points ▪ All of your simple machines are labeled = 4 points ▪ Your machine performs the task without assistance from you = 4 points In other words, if your machine includes three of each simple machine, they are all labeled, and it works without assistance, you will earn 20 extra credit points on any assignment, test, homework, etc! Henderson, 2002-2003 Name(s):________________________________________ Name of device:__________________________________ Task it will complete: _____________________________ ________________________________________________ Your Rube Goldberg Machine Checklist Simple Machine 1 2 3 Labeled? Pulley Lever Inclined Plane Wheel and Axle Scoring: + from checklist = working without assistance your points An illustration of a Rube Goldberg device pouring a cup of water Henderson, 2002-2003