WILLMAR PUBLIC SCHOOL 2013-2014 EDITION

HIGH SCHOOL SCIENCE

Physical Science 4:Simple Machines

CHAPTER 4

Simple MachinesIn this chapter you will: 1. Describe the conditions that must exist for a force to

do work on an object.2. Describe power.3. Describe what a machine is and how it makes easier

to do work.4. Relate the work input to a machine to the work out-

put of the machine.5. Explain why efficiency of a machine is always less

than 100%.6. Name, describe, and give an example of each of the

six types of simple machines.7. Describe how to determine the machine advantage of

each type of simple machine.8. Define and identify compound machines.

LOREM IPSUM

1. Lorem ipsum dolor sit amet

2. Consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

3. Ut enim ad minim veniam, quis exercitation ullamco laboris nisi ut aliquip ex commodo consequat.

4. Duis aute irure dolor in in voluptate velit esse cillum dolore eu fugiat nulla pariatur.

SECTION 4.1

Work & PowerYou probably do many kinds of work. You may do work for school. You may do work around your house, such as mowing the lawn. You may work at a job. But these things are not what scientists call work. For scientists, work has a special meaning.

In science, work is the product of force and distance. Work is the use of force to move an object. Work is only done when there is movement. Work is done when a force acts on an ob-ject in the direction the object moves. For a force to do work on an object, some of the force must act in the same direction as the object moves. If there is no movement, no work is done.

If you pushed as hard as you could against a heavy desk and the desk did not move, you would not be doing work. But car-rying a box is not work. When you carry a box, ou are using force to keep the box from falling. The force is an upward force. But the box is moving forward as you walk. The force and the motion are not in the same direction. So no work is being done.

Any part of a force that does not act in the direction of motion does no work on an object.

Work = Force x Distance

The product of force and distance results in the units of newton-meters, also known as joules. The joule (J) is the unit of work.

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OBJECTIVES:

1. Describe the connection that must exist for a force to do work on an object.

2. Describe power.

Vocabulary:

work

joule

power

watt

horsepower

Power is the rate of doing work.   Doing work at a faster rate requires more power.

To increase power, you can increase the amount of work done in a given time, or you can do a given amount of work in less time.

Power = Work / Time

The SI unit of power is the watt (W), which is equal to one joule per second. Power has another common unit of power, the horsepower. One horsepower (hp) is equal to about 746 watts.

Section Review:

1. When does a force do work?

2.If there is no movement, has work been done?

3.What is the equation for work?

4.What is the unit for work?

5. What is the equation for power?

6.What is the unit for power?

7. How are work and power related?

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LOREM IPSUM

1. Lorem ipsum dolor sit amet

2. Consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

3. Ut enim ad minim veniam, quis exercitation ullamco laboris nisi ut aliquip ex commodo consequat.

4. Duis aute irure dolor in in voluptate velit esse cillum dolore eu fugiat nulla pariatur.

SECTION 4.2

MachinesIt is easier to pull a large rock in a wagon than to push it on the ground. It is easier to tighten a nut with a wrench than with your fingers. It is easier to raise a car with a jack than to lift it yourself. A wagon, a wrench, and a jack are all ma-chines.

A machine is a device that changes a force. Machines make work easier to do. The six types of simple machines are the lever, the wheel and axle, the inclined plane, the wedge, the screw, and the pulley. They change the size of a force needed, the direction of a force, or the distance over which a force acts.

If a machine increases the distance over which you exert a force, then it decreases the amount of force you need to exert. Some machines decrease the applied force, but increase the distance over which the force is exerted. Some machines change the direction of the applied force.

Because of friction, the work done by a machine is always less than the work done on the machine. The force you exert on a machine is called the input force. The distance the input force acts through is known as the input distance. The work done by the input force acting through the input distance is called the work input.

The force that is exerted by a machine is called the output force. The distance the output force is exerted through is the output distance. The work output of a machine is the out-put force multiplied by the output distance.

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OBJECTIVES:

1. Describe what a machine is and how it makes work easier to do.

2. Relate the work input to a machine to the work output of the machine.

3. Compare a machine’s actual mechanical advantage to its ideal mechanical advantage.

4. Explain why the efficiency of a machine is always less than 100%.

Vocabulary:

machine output distance

input force work output

input distance actual mechanical advantage

work input ideal mechanical advantage

output force efficiency

The mechanical advantage of a machine is the number of times that the machine increases an input force. .

The actual mechanical advantage (AMA) equals the ratio of the output force to the input force. The ideal mechanical advantage (IMA) of a machine is the mechanical advantage in the absence of friction.  Because friction is always present, the actual mechanical advantage of a machine is always less than the ideal mechanical advantage.

Because friction reduces mechanical advantage, engineers of-ten design machines that use low-friction materials and lubri-cants. The percentage of the work input that becomes work output is the efficiency of a machine. Because there is al-ways some friction, the efficiency of any machine is always less than 100 percent.

Section Review:

1. What three things do machines change to make a task easier to perform?

2.Why is work done by a machine always less than the work done by you?

3.How does the actual mechanical advantage of a machine compare to its ideal mechanical advantage?

4.What happens to the efficiency of a machine if you reduce the friction?

5. Why can no machine be 100% efficient?

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LOREM IPSUM

1. Lorem ipsum dolor sit amet

2. Consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

3. Ut enim ad minim veniam, quis exercitation ullamco laboris nisi ut aliquip ex commodo consequat.

4. Duis aute irure dolor in in voluptate velit esse cillum dolore eu fugiat nulla pariatur.

SECTION 4.3

Simple MachinesThere are thousands of different kinds of machines. You use machines every day. But did you know that all machines are based on only six kinds of simple machines. The six types of simple machines are the lever, the wheel and axle, the inclined plane, the wedge, the screw, and the pulley.

A lever is a rigid bar that is free to move around a fixed point. The fixed point the bar rotates around is the fulcrum. If you push down on the end of one kind of lever, the other end moves up. The input arm of a lever is the distance between the input force and the fulcrum. The output arm is the dis-tance between the output force and the fulcrum. Levers are classified into three categories based on the locations of the in-put force, the output force, and the fulcrum.

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OBJECTIVES:

1. Name, describe and give examples of each of the six types of simple machines.

2. Describe how to determine the ideal mechanical advantage of each type of simple machine.

Vocabulary:

lever wheel and axle

fulcrum incline plane

input arm wedge

output arm screw

first-class lever pulley

second-class lever fixed pulley

third-class lever moveable pulley

pulley system

The position of the fulcrum identifies a first-class lever—the fulcrum of a first-class lever is always located between the input force and the output force. In a second-class lever the output force is located between the input force and the ful-crum. The input force of a third-class lever is located be-tween the fulcrum and the output force.

To calculate the mechanical advantage of any lever, divide the input arm by the output arm.

A wheel and axle is a simple machine that consists of two disks or cylinders, each one with a different radius. The outer disk is the wheel and the inner cylinder is the axle.

A wheel and axle is a lever rotated completely in a circle around the fulcrum. The axle is the smaller side, or output arm, of the lever. The wheel is the larger side, or input arm, of the lever.

To calculate the mechanical advantage of the wheel and axle, divide the radius (or diameter) where the input force is ex-erted by the radius (or diameter) where the output force is ex-erted.

An inclined plane is a slanted surface along which a force moves an object to a different elevation. Moving an object up an inclined plane requires less force than lifting it straight up, at a cost of an increase in the distance moved.

The mechanical advantage of an inclined plane is the distance along the inclined plane divided by its change in height.

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A wedge is a V-shaped object. A wedge sides are two inclined planes sloped toward each other.

A thin wedge of a given length has a greater ideal mechanical advantage than a thick wedge of the same length. The me-chanical advantage of a wedge is the distance along the wedge divided by its change in width.

A screw is an inclined plane wrapped around a cylinder. The mechanical advantage on a screw is calculated by the number of threads per centimeter. For two screws of the same length, the one whose threads are closer together moves forward less for each turn of the screw. Screws with threads that are closer together have a greater mechanical advantage. A screw with fewer threads per inch takes fewer turns to drive into a piece of wood or other material. But the smaller mechanical advan-tage of the screw requires you to exert a greater input force in order to drive it in.

A pulley is a simple machine that consists of a rope that fits into a groove in a wheel. Pulleys produce an output force that is different in size, direction, or both, from that of the input force.

The mechanical advantage of a pulley or pulley system is equal to the number of rope sections supporting the load be-ing lifted.

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A fixed pulley is a wheel attached in a fixed location. Fixed pulleys are only able to rotate in place. A movable pulley is attached to the object being moved rather than to a fixed loca-tion. By combining fixed and movable pulleys into a pulley system, a large mechanical advantage can be achieved.

Section Review:

1. What defines a first-class lever?

2.What defines a second-class lever?

3.What defines a third-class lever?

4.How do you calculate mechanical advantage for lever?

5. How is a wheel and axle like a lever?

6.How do you calculate mechanical advantage for a wheel and axle?

7. How does an incline plane make the effort on moving the object easier?

8.How do you calculate mechanical advantage for an inclined plane?

9.How is a wedge like an inclined plane?

10.How do you calculate mechanical advantage for wedge?

11.How do you calculate the mechanical advantage for the screw?

12.How do you calculate the mechanical advantage for the pulley?

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SECTION 4.4

Compound MachinesMost of the machines you use every day are actually a combi-nation of simple machines working together. A compound machine is a combination of two or more simple machines that operate together. Many familiar compound machines, such as a car, a washing machine, or a clock, are combinations of hundreds or thousands of simple machines.

Compound machines can make works even easier than simple machines. In a compound machine, the force you pass on to one simple machine is made larger and passed on to another simple machine. In this way, the total force is made much larger.

Compound machines are all around you. A scissors is a com-pound machine. It is simple two levers, with the fulcrum where the pin is located. A can opener is a compound ma-chine. The two handles are levers. The key you turn to open a can is a wheel and axle. The blade that cuts into the can is a wedge. A bicycle is another compound machine. Its wheels are connected to axles. So they made a wheel and axle ma-chine. The brake handles are levers.

A machine cannot make energy. But every machine needs en-ergy. When you pedal a bicycle, you provide the energy. Many machines use electric energy. All machines waste en-ergy. Remember that friction is a foce that resists motion. Ma-chines usually have moving parts that rub against each other. Friction slows down the motion of the parts. So energy is wasted. The work done by a machine is always less than the work put into it.

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OBJECTIVES:

1. Describe and identify compound machines.

2. Describe how compound machines make work easier.

Vocabulary:

compound machine

Section Review:

1. How do compound machines make work easier than simple machines?

2.How is the work done by a machine compare to the work put into it?

3.Give an example of a compound machine and describe the simple machine in it?

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