# Shared Flashcard Set

## Details

Mechanical Comprehension
Forces, Levers, Gears, and Pulley's
63
Physics
01/09/2012

Term
 Work
Definition
 Force applied over a specific distance.
Term
 Energy
Definition
 Ability to do work.
Term
 Kinetic Energy
Definition
 Energy in a moving object.
Term
 Potential Energy
Definition
 Energy that can be released under certain conditions. For Example, potential energy is stored in objects when they are lifted off the ground. It is released when the object falls.
Term
 Chemical Energy
Definition
 Energy stored in chemicals, such as in a flashlight battery. Chemical energy is potential until it is released in a chemical reaction.
Term
 Electric energy
Definition
 Energy in moving electrons in a electric current.
Term
 Force
Definition
 Push or Pull. A force has a magnitude (strength) that you can measure, and it has a direction.
Term
 Gravity
Definition
 Attractive force between objects.
Term
 Acceleration
Definition
 Change in velocity.
Term
 Velocity
Definition
 Speed and Direction.
Term
 Friction
Definition
 Force that results from the interaction between two surfaces that are touching each other. Friction acts as a resistance to the movement of an object.
Term
 What is the formula to measure force?
Definition
 Force = Mass × Acceleration
Term
 Compression
Definition
 Force that pushes materials together.
Term
 Tension
Definition
 Force that pulls materials apart.
Term
Definition
Term
 Fulcrum
Definition
 Stationary element that holds the lever but still allows it to rotate.
Term
Definition
 Object to be lifted or squeezed.
Term
Definition
 The part of the lever from load to fulcrum.
Term
 Effort
Definition
 Forced applied to lift or squeeze.
Term
 Effort arm (effort distance)
Definition
 Part of the lever from force to fulcrum.
Term
 [image] Class 1 Lever
Definition
 In a class 1 lever, the fulcrum is between the load and the effort. If the fulcrums is closer to the load than to the effort (as it usually is), the lever has a mechanical advantage.
Term
 [image]
Definition
 In a class 2 lever, the load is between the effort and the fulcrum. the effort arm is as long as the whole lever, but the load arm is shorter.
Term
 [image]
Definition
 In a class 3 lever, the effort is between the load and the fulcrum.
Term
 [image]
Definition
 (2 kg × 8 ft) + (4 kg × 6 ft) = (8 ft × F) 16 + 24 = 8F 40 = 8F F = 5 kg
Term
 [image]
Definition
 The figure shows a pulley attached to a beam that is used to hoist a heavy crate. Each foot of pull on the rope lifts the crate 1 foot. Effort distance = load distance, so MA = 1. Although this pulley allows you to pull down instead of up, it gives no me- chanical advantage.
Term
 [image]
Definition
 The simplest way to find the pulley MA is to count the strands of rope on the movable pulley (in this case, the one attached to the load). MA = number of supporting strands.
Term
 Gears
Definition
 Gears are a simple machine used to multiply rotating forces. Finding the MA of a gear is simplicity itself. Identify the driving gear (the one that supplies the force) and count the teeth. Count the teeth on the driven gear. Then use this formula: Number of teeth on driven gear/number of teeth on driving gear = MA
Term
 Sheaves
Definition
 Sheaves (often also called pulleys) and belts are a simple machine closely related to gears. To calculate the MA of a sheave system, divide the diameter of the driven sheave by the diameter of the drive sheave: MA = driven diameter/drive diameter Whenever the driven sheave is larger than the drive sheave, you get a mechanical advantage.
Term
 [image]
Definition
 Example of Sheave System.
Term
 Inclined Plane
Definition
 Inclined plane is a fancy term for “ramp.” An inclined plane is another simple machine that is used to lift heavy objects. The formula for finding the mechanical advantage of an inclined plane is as follows: MA = length of the slope/vertical rise To find the mechanical advantage, measure vertically and diagonally along the ramp.
Term
 The figure shows an inclined plane. What is the mechanical advantage? If the load weighs 400 lb, how much force is needed to push it up the ramp?   [image]
Definition
 MA = 12/3 =  4   MA = load/effort 4 = 400/effort 4 × effort = 400 Effort = 100 lb
Term
 Wedge
Definition
 The wedge is a type of inclined plane. It is one of the rarer simple machines. As always, MA = effort distance/load distance. The wedge is essentially two inclined planes, and the MA calculation also requires you to measure perpendicular to the long axis of the wedge.
Term
 The figure shows a wedge. What is the MA? [image]
Definition
 Every time the wedge moves 5 inches, the load will move 2 inches. MA = 5/2 = 2.5. In reality, friction plays a major role in wedges.
Term
 Screw
Definition
 Screws are some of the handiest simple machines, although we usually think of a screw as a fastener rather than as a way to multiply force. Finding mechanical advantage can be complicated because it comes from two sources: the threads and the wrench you use to tighten the screw. But if you consider effort distance and load distance, the calculation is simple. MA = effort distance/load distance
Term
 [image]
Definition
 The figure shows an 8-inch wrench turning a screw with 8 threads per inch. This screw has a pitch (movement per turn of the screw) of 1/8 inch. The effort distance is ∏ ×diameter = 3.14 ×16 inches = about 50 inches. The load distance per turn of the wrench is 1/8 inch, so MA = 50/1/8 = 400. In reality, the MA is much less, because of friction and because you don’t push on the absolute end of the wrench.
Term
 Wheel and Axle
Definition
 Wheels are a common and essential part of daily life, but most of these wheels are not simple machines. Instead, they are a way to reduce friction by the use of bearings. A wheel and axle is a simple machine only when the wheel and axle are fixed and rotate together. For wheel- and-axle machines, mechanical advantage is calculated as follows: MA = effort distance (radius of the wheel)/load distance (radius of the axle)
Term
 The figure shows a brace and bit, a kind of heavyduty screwdriver that is an example of a wheel and axle as a simple machine. What is the MA? [image]
Definition
 Effort distance/load distance = MA 6 in./0.25 in. = 24 MA = 24
Term
 Compound Machine
Definition
 A compound machine is one in which two or more simple machines work together. For example, a screwdriver (wheel and axle) driving a screw is a compound machine. To find the mechanical advantage of a compound machine, multiply the MA of the simple machines together.
Term
 Structural Support
Definition
 When a load of any kind is supported by two support beams, posts, or people, the load is perfectly balanced if it is exactly centered. In that case, each beam, post, or person is bearing exactly half the load. However, if the load is not centered, then the beam, post, or person nearer to the load is bearing the greater part of the weight.
Term
 Which of these four shelves can bear the most weight? [image]
Definition
 Choice D can bear the most weight. Of the four shelves, it is the strongest because it has the largest brackets, and because it has the most brackets.
Term
 Which bridge is the strongest? [image]
Definition
 In the diagram, bridge C is the strongest because its framework is made of many triangles.   A structure in which the support beams form rectangular shapes is not as strong as one in which the beams form triangular shapes. The reason is that while rectangular supports can easily bend out of shape, a triangle keeps its shape unless it falls apart entirely. That’s why triangular shapes are used in support structures such as shelf brackets. That is also why you often see triangular shapes in the support structures of bridges, towers, and other buildings.
Term
 What is the formula to calculate the speed of a particular pulley in a system of pulleys?
Definition
 Speed1 × Diameter1= Speed2 × Diameter2   (Note that pulley speed is measured in revolutions per minute, or rpm.)
Term
 Pulley 1 measures 9 in. in diameter. Pulley 2 meas- ures 3 in. in diameter. If pulley 1 rotates at 1,200 rpm, how fast will pulley 2 rotate?
Definition
 Speed1 × Diameter1 = Speed2 × Diameter2   1,200 × 9 = 10,800 = Speed2 × 3 Speed2 = 10,800/3 = 3600 Another way to calculate the speed of pulley 2 is to look at the ratio between the two diameters. A ratio of 9:3, or 3:1, will multiply speed × 3. So 1,200 rpm × 3 = 3,600 rpm. Remember that the pulley with the smaller diameter is always the one that rotates faster!
Term
 When pulley A runs at 400 rpm, what will be the speeds of pulleys B, C, and D? [image]
Definition
 In this system, assume that the linked pulleys (B and C in the example) run at the same rpm, since they are attached to the same shaft. Break the problem down into parts, and calculate them in order: ●  Diameter of pulley A/diameter of pulley B = 4/8, so pulley B will run 1/2 as fast as pulley A.   400/2  = 200 rpm ●  You already know that pulley C runs at the same speed as pulley B. ●  Diameter of pulley C/diameter of pulley D = 4/16 = 1/4, so pulley D will run 1/4 as fast as pulley C.   200/4 = 50 rpm
Term
 System of Gears
Definition
 The gears in a system typ- ically have different diameters and different numbers of teeth per gear. The teeth of one gear mesh with the teeth of another, and as one gear (the driving gear) turns, it turns the other gear (the driven gear). When interlocking gears have different numbers of teeth, the gear with fewer teeth will rotate more times in a given period than the gear with more teeth.
Term
 Gear A and gear B make up a system of gears. If gear A makes 6 revolutions, how many revolutions will gear B make? [image]
Definition
 To solve this problem, use the picture and your common sense. Count the teeth on each gear. Gear A has 9 teeth. Gear B has 27 teeth. The ratio of the teeth on the two gears is 9:27 or 1:3. Common sense should tell you that gear A must rotate 3 times to make gear B rotate once. So if gear A rotates 6 times, gear B will rotate twice. Always keep in mind that in this kind of system, the gear with more teeth makes fewer rotations in the same period than the gear with fewer teeth.
Term
 Idler Gear
Definition
 Notice, too, that gears change the rotation direction, while pulleys usually do not. To rotate a gear in the same direction as the driving gear, you need a third gear, called an idler gear.
Term
 Pin and Slot Arrangement
Definition
 In this arrangement, a pin is attached to a driving shaft, and a slotted disk is attached to a driven shaft. When the driving shaft rotates, the pin enters a slot on the disk and turns the driven shaft.
Term
 In this pin and slot arrangement, each time the driv- ing shaft turns one full revolution, the disk on the driven shaft will make 1/4 revolution. How far will the disk rotate when the pin turns three complete revolutions? [image]
Definition
 3 × 1/4 = 3/4 turn
Term
 Which point will travel farthest as the wheel makes 10 rotations? [image]
Definition
 Point B will travel farthest because it is farthest from the center. The distance it travels in each rotation is greater than the distance traveled by the other points.
Term
 Cams and Cam Followers
Definition
 Cams are lobes attached to rotating shafts to push separate pieces, called cam followers. Cams are often found in engines, where they push intake and exhaust valves open when the engine turns. For every complete rotation of the camshaft, the cam follower will move away from and then back to its original position. A spring pushes the follower tight to the cam. [image]
Term
 Cranks and Pistons
Definition
 Cranks are used to change motion in a straight line to motion in a circle. You’ll find cranks connected to pedals on a bike, and to pistons in a car engine. When a crank makes one complete revolution, the piston must go up and down and return to its original position. [image]
Term
 Air Pressure
Definition
 Air pressure is measured in pounds per square inch. Atmospheric pressure at sea level is 14.7 lb/in2, which is actually quite a bit of pressure. Since it’s present all around us, we don’t notice it. However, if you create a vacuum inside a weak container, the container will be crushed by all that pressure.
Term
 Pneumatic Systems
Definition
 Systems that use compressed air to do work are called pneumatic systems. Air is easily compressed, and the calculations are more complicated than they are with liquids, which usually can’t be compressed. The larger the driven cylinder, the more air pressure it is exposed to, and the greater the force it can exert.
Term
 Gas Laws
Definition
 The “gas laws” apply to air as it is compressed and expanded. ●  When a gas is compressed, it gains thermal energy—it warms up. The gas also gains potential energy, which is why compressed air can be used to drive nail guns and pneumatic hammers. ●  When a given amount of gas expands, its pressure drops and the gas cools. ●  When a gas cools without a change in outside pressure, it loses volume.
Term
 Gas Laws Examples
Definition
 What happens when you increase the air pressure outside a balloon? The balloon shrinks until the pressure inside becomes great enough to balance the pressure outside. Air pressure is also what keeps airplanes aloft. The bulge on the top of an airplane wing increases the speed of air passing over the wing, and that causes a reduction in pressure. Because air pressure does not change below the wing, the result is an unbalanced upward force. This force lifts the airplane. [image]
Term
 Refridgerators
Definition
 A compressor compresses a fluid, called a refrigerant. The refrigerant warms up, as predicted by the gas laws. Then the refrigerant loses heat (but not pressure) in the condenser. The refrigerant is piped into an evaporator, where it goes through a small hole and evaporates under reduced pressure. Expansion causes the temperature to drop, and the cold refrigerant can pick up heat from the surroundings. This is why the evaporator is placed in the area to be cooled. The condenser is placed where it’s easy to get rid of excess heat—in the backyard for an air conditioner, or in back for a refrigerator.
Term
 Water Pressure Principles
Definition
 Total flow through a pipe system must be the same everywhere because water cannot be com- pressed. When liquid speeds up, pressure falls. When liquid slows down, pressure rises. In the diagram, the same amount of water isflowing everywhere in the pipe system. For this to be true, water must be flowing faster at point B than at point A. That means that pressure is lower at point B. [image]   Water in a container also exerts pressure on the bottom of the container. The deeper the water, the greater the pressure. To find the amount of water pressure in a tank, calculate the total weight of the water and divide by the area of the base of the tank.
Term
 A tank with a base that measures 2 feet × 4 feet holds 1,600 pounds of water. What is the water pressure at the base of the tank?
Definition
 2 ft × 4 ft = 8 ft2 1,600 Ib/8ft2 = 200 lb/ft2 Remember too that 1 ft2 = 144 in2. To convert pressure between pounds per square inch and pounds per square foot, divide or multiply by 144.
Term
 Water is being piped into a tank at the rate of 2 gal- lons per second. At the same time, it is being piped out of the tank at the rate of 60 gallons per minute. How many gallons will be added in 5 minutes? [image]
Definition
 Convert the inflow rate so that you are working only with gallons per minute. gal/sec × 60 = gal/min 2 gal/sec × 60 = 120 gal/min Subtract: 120 gal/min inflow − 60 gal/min outflow = 60 gal/min net gain The net gain in 5 minutes is 5 × 60 = 300 gallons.
Term
 A 100-gallon tank contains 10 gallons of water. Water is added through one pipe at the rate of 3 gallons per minute. It is drained away through another pipe at the rate of 2 gallons per minute. How long will it take to fill the tank?
Definition
 Find the net gain of water per minute:   3 gal/min – 2 gal/min = 1 gal/min It will take 100 − 10 = 90 gallons to fill the tank. At the rate of 1 gal/min, it will take 90 minutes to fill the tank.
Term
 Glossary
Definition
 Chemical Energy: Energy stored in chemicals or released in a chemical reaction Compression: A force that pushes materials together Compound Machine: A machine made up of two or more simple machines working together Effort: In a lever, the point where you apply force Effort Arm: In a lever, the distance from the force to the fulcrum Electrical Energy: Energy in moving electrons Flexibility: The ability of a material to bend without breaking Friction: The force that resists the relative motion of two surfaces in contact Fulcrum: The stationary element that holds a lever but also allows it to rotate Gravity: An attractive force between objects Kinetic Energy: Energy in a moving object Load: In a lever, the part where output force lifts or squeezes Load arm: In a lever, the distance from the load to the fulcrum Mechanical Advantage: The amount by which a machine multiplies the force applied to it Potential Energy: Energy that can be released under certain conditions Tension: A force that pulls materials apart
Term
 Laws and Formulas to Know
Definition
 How to calculate mechanical advantage (MA): Lever: MA = load/effort = effort distance/load distance Pulley: MA = load/effort = number of supporting strands Gears: MA = number of teeth on driven gear/ number of teeth on driving gear Sheaves: MA = driven diameter/drive diameter Inclined plane: MA = horizontal length/vertical rise Wheel and axle: MA = radius of wheel/radius of axle Speed of pulleys in a system: Speed1× Diameter1 = Speed2 × Diameter2 The gas laws: When a gas is compressed, it heats up. When a given amount of gas expands, its pressure drops and the gas cools. When a gas cools without a change in outside pressure, it loses volume. Water pressure: Total flow through a pipe system is the same everywhere. When liquid speeds up, pressure falls. When liquid slows down, pressure rises.
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