CHAPTER 8 MACHINES Machines make work easier by

CHAPTER 8 MACHINES

• Machines make work easier by changing the force you exert in size or direction, or both. • But it does not change the amount of work done. • A machine is a device that makes work easier.

Types of Machines • • • Lever Inclined Plane Pulley Wheel and Axle Wedge Screw

SIMPLE MACHINES Do work with one movement COMPOUND MACHINES Are a combination of two or more simple machines.

MACHINES SIMPLE MACHINES INCLINED PLANE TYPE LEVER TYPE • Inclined Plane • Screw • Wedge • Lever • Wheel & Axle • Pulley COMPOUND MACHINE AXE Wedge and Lever

EFFORT FORCE (Fe) is the force you exert on a machine * RESISTANCE FORCE (Fr) is the force applied by the machine to overcome resistance. * EFFORT DISTANCE (de) is the distance moved by the effort force. * RESISTANCE DISTANCE (dr) is the distance moved by the resistance force.

WORK INPUT (Win) is the work put into the machine WORK OUTPUT (Wout) is the work that the machine puts out.

IDEAL MACHINE

MECHANICAL ADVANTAGE (MA) is the number of times a machine multiplies the effort force. IDEAL MECHANICAL ADVANTAGE (IMA)

EFFICIENCY An ideal machine has an efficiency of 100%. Machines have efficiency of < 100%

Machines make work easier by changing the force you exert in size and/or direction.

LEVERS A lever is a bar that is free to pivot, or turn, about a fixed point. The fixed point of a lever is called the fulcrum. EFFORT FORCE RESISTANCE FORCE FULCRUM

LEVERS The part of the lever on which the effort force is applied is called the effort arm. The part of the lever that exerts the resistance force is called the resistance arm. EFFORT ARM RESISTANCE ARM

LEVERS EFFORT ARM RESISTANCE ARM

FIRST CLASS LEVER The fulcrum is always in between the effort force and the resistance force. Examples: seesaw, hammer, hair clip, bottle opener, crow bar and cart

FIRST CLASS LEVER EFFORT FORCE EFFORT ARM RESISTANCE FORCE

SECOND CLASS LEVER The resistance is located between the effort force and the fulcrum. They always multiply effort force. Examples: nutcracker, wheelbarrow, hole puncher, bottle opener, lemon squeezer

SECOND CLASS LEVER EFFORT FORCE EFFORT ARM RESISTANCE FORCE

THIRD CLASS LEVER The effort is located between the resistance force and the fulcrum. They do not multiply effort force. Examples: rake, broom, fishing pole, your arm, and hockey stick

THIRD CLASS LEVER EFFORT FORCE RESISTANCE ARM EFFORT ARM RESISTANCE FORCE

THIRD CLASS LEVER EFFORT FORCE RESISTANCE ARM EFFORT ARM RESISTANCE FORCE Effort arm is always shorter than the resistance arm, so it cannot multiply force. It’s MA is always less than 1.

LEVERS WITH A HUMAN TOUCH First Class Lever Your neck muscles support the effort force to hold up the resistance weight of your head. Second Class Lever Tip of your feet-Fulcrum Weight -Resistance Muscles- Effort

LEVERS WITH A HUMAN TOUCH Third Class Lever R E F Elbow-Fulcrum Biceps-Effort Weight-resistance

PROBLEM #1 A lever uses a force of 250 N to move a rock that weighs 3000 N. Find the mechanical advantage of using the lever.

PROBLEM #3 A simple machine allows a worker to move an effort distance 45 cm in order to move a resistance distance 20 cm. What is the ideal mechanical advantage of the machine?

PULLYING WITH PULLEYS A pulley is a grooved wheel with a rope or a chain running along the groove. A pulley works something like a first class lever. Instead of a bar a pulley has a rope. The axle of the pulley acts like the fulcrum. The two sides of the pulley are the effort arm and the resistance arm.

SINGLE FIXED PULLEY • It is lifted the same distance as it is pulled at the other end of the rope. • Example: flagpole, blinds. • Force is not multiplied. There is only a change in the direction of the force applied. W F

SINGLE MOVABLE PULLEYS • Force is multiplied. IMA = 2, since two wires are supporting the resistance. The effort distance must be twice as large as the resistance distance. Example: construction cranes. F W

BLOCK AND TACKLE • It is combination of fixed and movable pulley. • It can produce large enough force to lift automobiles.

WHEEL AND AXLE Wheel and axle is a simple machine consisting of two wheels of different sizes that rotate together. Examples: doorknob, faucets, handles, steering wheel of a car etc. An effort force is applied to the larger wheel. The smaller wheel, called the axle, exerts the resistance force. It allows us to use less force to do work.

WHEEL AND AXLE Gear is a modified wheel and axle machine. It is wheel with teeth along its circumference. Effort is exerted on one of the gears and the other gear turns.

INCLINED PLANE Slanting boards and ramps are called inclined planes. They are sloping surfaces used to raise objects. W=weight, H=height, L=length, F=force L H F W

L H F W

PROBLEM #5 What is the ideal mechanical advantage of a ramp 4 cm long and 2 cm high?

PROBLEM #8 What is the efficiency of a machine with work input 1000 J and work output 700 J?

SCREWS Screw is another form of inclined plane. The threads form a tiny ramp that runs from its tip to near its top. As you turn the screw, the threads seem to pull the screw into the wood.

SCREWS When a screw is turned , it moves forward. At the same time, it presses against the material around it. Many turns are needed to move the screw a short distance. But the screw produces a far greater force than the force needed to turn it.

WEDGE Wedge is a form of inclined plane. It is a moving inclined plane. The material remains in one place while the wedge moves through it. Examples: blade of an axe, knife blade, razor blade, door stop, chisel.