1 Ch 14 Machines 14.1 Machines help people do work

2 Machines change the way force is applied Machine—device that helps people do work. It does not change the amount of work done If a machine decreases the amount of force needed to do the work, the distance over which that force is applied increases A machine can change the direction of an applied force

3 Input force—force exerted on a machine. Output force—force exerted on an object by a machine Mechanical advantage=# of times a machine multiplies the input force

4 Work transfers energy A machine increases the potential or kinetic energy of an object by doing work on it *For a certain amount of work, if distance increases, force decreases

5 Output work is always less than input work Efficiency (%) = output work/input work X 100 No real machine is 100% efficient. Machines lose energy to friction, which is why we lubricate moving parts. Another source of loss of efficiency is air resistance, which is the reason for str5eamlined designs for vehicles & cyclists’ helmets

Six Simple Machines Have Many Uses The lever & inclined plane are the 2 main types of simple machines Other simple machines are based on these.

7 Other Simple Machines 1.Lever—solid bar that rotates on a fixed point called the fulcrum *There are 3 classes of levers based on the relative locations of the input force, output force, & fulcrum

8 2. Wheel & axle—wheel is attached to a shaft & acts like a rotating collection of levers *Input force can be applied to either part, which transfers force to the other part

9 3. Pulley—wheel with an axle & a grooved rim. A rope or cable moves in the groove. Pulleys can be fixed or movable. A combination of both is called a block & tackle

10 4. Inclined plane—sloping surface that supports the weight of an object while the object moves from one level to another

11 5. Wedge—has a thick & thin end; can be used to cut, split, pierce, or hold objects together

12 6. Screw—incline plane wrapped around a cylinder or cone to form a spiral; can be used to hold things together or raise/lower objects

13 The mechanical advantage of a machine can be calculated If a machine were 100% efficient, its ideal mechanical advantage would be output force divided by the input force MA = F out F in

14 MA Inclined plane Divide the length of the incline by the height of the incline

15 MA Wheel & axle Divide the radius where the input force is applied by the radius where the output force is applied

16 MA Lever Calculate by dividing distance from input force to fulcrum by the distance from output force to fulcrum

Modern Technology Uses Compound Machines Compound machines are combinations of simple machines They often have many moving parts & must overcome more friction than simple machines

18 Compound Machines (cont’d) Their MA equals the product of the MA of all the simple machines that make it up Example: If a lever with a MA of 2 acts in series with a lever with MA of 3, the MA of the lever combo will be 2 x 3, or 6

19 MA of a gear system comprising 2 wheel –and –axle systems… Is found by dividing the # of teeth on the output wheel by the # of teeth on the input wheel. Example A wheel with 16 teeth turns another wheel with 24 teeth. The wheel with 16 teeth is the input wheel & the one with 24 teeth is the output wheel: MA = = 1.5

20 Modern Technology Creates New Uses For Machines Sophisticated machines are often based on, or contain, several simple machines Machines built from individual atoms & molecules of material are the result of nanotechnology *Most nanomachines are still in the experimental stage

21 Robots are machines that work automatically or by remote control. They do jobs in places where it is difficult or dangerous for people to do work

22 MA Pulleys MA is equal to the # of ropes that support the weight