Machines Making Work Easier Machines A device that

Machines Making Work Easier

Machines • A device that makes work easier o Some powered by engines/motors, others powered by people • What are some examples?

Machines • Simple Machine = a device that does work with only one movement o 6 types

Advantages of Machines • They make work easier by… 1. Multiplying the effort force 2. Changing the direction of the applied force you exert 3. Increasing the distance through which the resistance force moves 4. Overcoming gravity and friction

Applying Force and Doing Work • Effort Force = the force applied to a machine • Resistance Force = the force applied by the machine to overcome resistance

Review • Where is the effort force? • Where is the resistance force? C B A

Applying Force and Doing Work • W = Fd (Work = Force x distance) • Measured in Joules (J) • You push a box with a force of 200 N. The box moves 1 m. How much work did you do? • W = 200 N x 1 m • W = 200 J

Applying Force and Doing Work • A girl lifts a 12 N weight 1. 5 m. How much work does she do on the weight? • F= • d= • W = Fd

Applying Force and Doing Work • Remember, energy is always conserved so… • You never get more work out than you put in • Win = Wout (in an ideal machine) • Why will work out always be smaller?

The Simple Machines

Levers • A bar that is free to pivot, or turn, about a fixed point • Fulcrum = the fixed point of a lever • Effort Arm = the part of the lever on which the effort force is applied • Resistance Arm = the part of the lever that exerts the resistance force

Levers • Teeter-totters, can openers, tennis rackets • Helps you do more work with the strength you already have

3 Types of Levers • First Class = fulcrum is between the effort and resistance forces (teetertotter) o Multiplies the effort force and changes its direction o Effort moves farther than Resistance

st 1 Class Lever • When the fulcrum is closer to the effort than to the load: o There is a loss in force o There is a gain in speed and distance

st 1 Class Lever • When the fulcrum is closer to the load than to the effort: o There is a loss in speed and distance o There is a gain in force.

st 1 Class Lever • When the fulcrum is midway between the effort and the load: o There is no change in force, speed, or distance

3 Types of Levers • Second Class = resistance is located between the effort force and the fulcrum (wheelbarrow) o Always multiplies effort force o Effort moves farther than Resistance

3 Types of Levers • Third Class = effort force is located between the resistance force and the fulcrum (fishing pole) o Increases speed (cannot multiply the force) o Resistance moves farther than Effort o Multiplies the distance the effort force travels

How well do you know your levers? A. 1 st class B. 2 nd class C. 3 rd class

Pulleys • A grooved wheel with a rope, chain, or belt running along the groove o Examples: Flagpole, blinds • The two sides of the pulley are the effort arm and resistance arm • What does a pulley do? 1. Changes the direction of the force 2. Makes it easier to lift things to high-rise areas

3 Types of Pulleys • A fixed pulley is attached to something that does not move. • Changes the direction of the effort force. • Disadvantage: to have to apply more effort than the load

3 Types of Pulleys • A movable pulley moves with the load o May be attached to a construction crane • Does multiply the effort force • Cannot change the direction of the effort force

Movable Pulley • Disadvantage: have to pull or push the pulley up or down • Advantage: Less effort to pull the load

3 Types of Pulleys • Block and Tackle Pulley = a movable pulley and a fixed pulley • The effort needed to lift the load is less than half the weight of the load

Block and Tackle Pulley • Advantage: effort is less than half of the load • Disadvantage: travels a very long distance

Wheel and Axle • A lever that rotates in a circle around an axle o Two wheels of different sizes connected – the axle being the smaller wheel o Larger wheel may be a crank handle or faucet handle • Examples: door knob water faucet

Wheel and Axle • A gear is a wheel with teeth along its circumference • Effort is exerted on one gear to cause the other gear to turn

Inclined Plane • A plane is a flat surface • Inclined plane is a plane that is slanted • Example: Ramp • Used to move things from a lower to a higher place or vice versa

Inclined Plane How does the amount of work done with a ramp compare to the amount of work done lifting the object? • Work will be the same • Force to lift would be greater than the force used to push • Distance pushed up the ramp would be farther than the distance lifted • Not less work, but less effort

Screw • An inclined plane wrapped around a cylinder • Multiplies an effort force by acting through a long effort distance • The closer the threads on a screw, the greater the mechanical advantage • The plan actually slides through the wood

Wedge • An inclined plane with one or two sloping sides that moves • The wedge is used to increase force • The material remains in place while the wedge moves through it • A wedge changes the direction of the input force

Wedge • Examples: ax, knife, chisel • The “sharper” the wedge, the greater the mechanical advantage • Can be used to split, cut, or fasten (nail/doorstop)

Compound Machines • A combination of two or more simple machines • Examples: o o Lawn mower Pencil sharpener Ax Bicycle