Unit D: Mechanical Systems Topic 1: Levels and Inclined Planes

Transcription

1 Unit D: Mechanical Systems Topic 1: Levels and Inclined Planes Photo from educatorsoutlet.com 1

2 A. Introduction 1. Lever a) Is a rigid bar or plank that can rotate around a fixed point called a pivot, or. b) Levers are used to reduce the needed to do a particular task. c) You can move a very large load, but you must move a greater than the load moves. Photo from makeitgo.wikispaces.com 2. The fulcrum the load. 3. The force exerted on the lever to make it move is called the force. 4. The mass of the object lifted by the lever is called the. 5. There are classes of levers: a) Class Lever Photo from uaf.edu Photo from umn.edu 2

3 b) Class Lever Photo from uaf.edu Photo from katapultdesign.com.au c) Class Lever Photo from uaf.edu Photo from builtforhockey.com 6. The distance between the fulcrum and the effort force is called the effort. 7. The distance between the fulcrum and the load is called the arm. load effort force load arm fulcrum effort arm B. Bones and Muscles: Built-in Levers 1. Most of the in your body are 3 rd class levers, but there are 1 st and 2 nd class levers as well. 3

4 2. Your bones act as levers with the acting as the fulcrum. 3. Tendons exert the effort force on the. The load is what is being moved (see the examples in your textbook on p. 274). C. An Arm in Space 1. Since its maiden voyage aboard U.S. Space Shuttle Columbia in 1981, the Shuttle Remote Manipulator System ( ), has demonstrated its reliability, usefulness, and versatility and has provided strong, yet precise and delicate handling of its payloads. Photo from militaryphotos.net 2. Usually called the - the Space Shuttle Remote Manipulator System is an application of levers in space technology. 3. It has been used in different Space Shuttles to help launch and retrieve or repair the Hubble Space Telescope from the shuttle s cargo bay. 4. A more complex version - has been installed on the International Space Station It is the Mobile Servicing Station component of the Space Station. Photo from science.nasa.gov 4

5 D. What is Work? 1. Scientifically, work is done when a acts on an object to make that object. 2. In order to say that work is being done, there must be. 3. If there is no movement, no matter how much force is used, work is done. Direction of the force applied to an object Direction of movement as a result of the force being applied to the object Object being moved 4. For example, a worker uses force to move a large carton up a ramp. (pushing) is transferred to the carton from the worker. Thus, we say that the worker did work on the carton as long as the carton moved up the ramp as a result of the worker s pushing action (force). E. Calculating Work 1. The amount of work (W) is by multiplying the force (F) times the distance (d) the object moves. 2. The formula looks like this: 3. Force is measured in and distance is measured in. 4. The resulting work unit is called a, named after the English scientist James Joule. F. Energy and Work 1. Energy and work are closely, because without energy there would be no work. 2. Work is done when there is a of energy and movement occurs. 5

6 3. Energy provides the force needed to make an move. 4. The energy can be in the form of energy (muscle power chemical reactions in the body producing energy) or it can be in the form of another energy source, such as gasoline (for a car). 5. A machine transfers energy from its to the object, causing the object to move. 6. There is a very chain of events that make a car move - beginning with it being fueled up with gasoline - all the way through its many subsystems (each doing work) - to eventually the tires rotating to make the car move forward or backward. G. The Inclined Plane 1. The inclined plane (or ), makes it easier to move a load higher than it is, but, it has to be moved over a much longer distance. 2. An inclined plane makes it possible to lift objects using a smaller force (examples: loading ramp, wheelchair access ramp). height it moves 2 m H. Work Input and Work Output distance the load moves: 12 m 1. Input Work a) When you do work on a machine such as a lever, the does work on a load. b) The you do on the machine is input work. 2. Output Work a) The work the machine does the load is the output work. 6

7 I. Mechanical Advantage 1. Mechanical Advantage is the of the force produced by a machine to the force applied to the machine (the size of the load vs. the size of the force needed to move the load). Mechanical Advantage MA = Load force F L Effort force F E 2. Example (page 278): Your truck gets stuck in the mud. You use a tree branch as a lever to lift the truck. Find the mechanical advantage if you apply an effort force of 500 N to the branch and the back of the truck weighs 2500 N. J. Another Way to Calculate Mechanical Advantage 1. The of mechanical advantage and work can be linked. MA= Load force F L Effort force F E = Effort arm Load arm MA= Effort arm Load arm 2. Example: Calculate the mechanical advantage (MA) if the effort arm is 3 m and the load arm is 0.3 m. 7

8 K. Speedy Levers 1. Speed is the rate of motion that an object changes position. 2. Class 3 levers are not very useful for the effort force, but rather they are useful because they provide a speed advantage. 3. Effort is produced that moves the load very over a relatively large distance. Change the direction of a force (a pulley on a flagpole) Increasing or decreasing speed (scissors) L. Machines Made to Measure 1. Body weight, height, size, age and gender are factors taken into account when designing for use by the consumer. 2. The science of designing machines to suit people is called. 3. Ergonomics is especially important in the design of work where occupational safety is an issue. 4. Carpal tunnel syndrome causes numbness and pain in the thumb and first three fingers, caused by the continuous movements of the fingers on the computer keyboard. 5. Ergonomically designed products include: 8