Simple Machines Introduction to

Objectives After completing this section, students will be able to: 1. Explain why we use machines, and compare and contrast a simple and a compound machine. 2. Name the six simple machines, and identify them in use in various common tools.six simple machines, and identify them in use in various common tools 3. Recognize and differentiate between the 3 types of levers.3 types of levers 4. Apply formulas to compute the efficiency and mechanical advantage of pulley and ramps, and levers.efficiency and mechanical advantagepulley and rampslevers 5. Explain how the use of a machine does not violate the law of conservation of energy.

What are they? Simple machines are machines with few or no moving parts that are used to make work easier

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

The 6 Simple Machines Lever Pulley Wheel and Axle WedgeScrew Inclined Plane

Why Use Simple Machines? For the mechanical advantage… Making something easier to do, but it takes a little longer to do it For example, going up a longer flight of stairs instead of going straight up a ladder

Complex Machines  Combining two or more simple machines to work together  Examples:  Car jack combines wedge and screw  Crane or tow truck combines lever and pulley  Wheel barrow combines wheel and axle with a lever

Energy: Ability to do work Work= Force x Distance Force: A Push or a Pull Definitions:

Equation to calculate the amount of Work done Work = Force x Distance Variables (W) (F) (d) W = F x d W = Fd

Units for each measurement  Work is measured in Joules (J)  Force is measured in Newtons (N)  Distance is measured in metres (m)  (or the most appropriate unit) IfW = F x d Then J = N x m (or Nm)

Work input and output  Work input is the amount of work done on a machine. (W in )  Input force x input distance  Work output is the amount of work done by a machine. (W out )  Output force x output distance 15 m 3 m W out = W in F out x D out = F in x D in 10N x 3m = 2N x 15m 10 N F in D in D out

Sample Questions

Mechanical Advantage

Lever  Makes lifting weight easier by using a fulcrum to redirect force over a longer distance  Examples: see-saw, dump truck, broom, crane arm, hammer claw, crow bar, fishing pole, screwdriver, bottle opener

Fulcrum is between EF (effort) and RF (load) Effort moves farther than Resistance. Multiplies EF and changes its direction. The mechanical advantage of a lever is the ratio of the length of the lever on the applied force side of the fulcrum to the length of the lever on the resistance force side of the fulcrum. First Class Lever

.  Common examples of first-class levers include crowbars, scissors, pliers, tin snips and seesaws.

RF (load) is between fulcrum and EF Effort moves farther than Resistance. Multiplies EF, but does not change its direction The mechanical advantage of a lever is the ratio of the distance from the applied force to the fulcrum to the distance from the resistance force to the fulcrum. Second Class Lever

 Examples of second-class levers include nut crackers, wheel barrows, doors, and bottle openers.

EF is between fulcrum and RF (load) Does not multiply force. Resistance moves farther than Effort. Multiplies the distance the effort force travels The mechanical advantage of a lever is the ratio of the distance from the applied force to the fulcrum to the distance of the resistance force to the fulcrum. Third Class Lever

 Examples of third-class levers include tweezers, arm hammers, and shovels.

Sample Questions

Inclined Plane  Makes it easier to move objects upward, but you have to go further horizontally  Examples: highway or sidewalk ramp, stairs, inclined conveyor belts, switchback roads or trails

Inclined Plane

 The Egyptians used simple machines to build the pyramids. One method was to build a very long incline out of dirt that rose upward to the top of the pyramid very gently. The blocks of stone were placed on large logs (another type of simple machine - the wheel and axle) and pushed slowly up the long, gentle inclined plane to the top of the pyramid.

Inclined Planes  An inclined plane is a flat surface that is higher on one end  Inclined planes make the work of moving things easier

Inclined Plane - Mechanical Advantage  The mechanical advantage of an inclined plane is equal to the length of the slope divided by the height of the inclined plane.  While the inclined plane produces a mechanical advantage, it does so by increasing the distance through which the force must move.

Mechanical Advantage of a Ramp

Sample Questions

Wedges  Two inclined planes joined back to back.  Wedges are used to split things.

Wedge  Pushes materials apart, cuts things  Examples: axe, doorstop, chisel, nail, saw, jackhammer, bulldozer, snow plow, horse plow, zipper, scissors, airplane wing, knife, fork, bow of a boat or ship

Wedge – Mechanical Advantage  The mechanical advantage of a wedge can be found by dividing the length of either slope (S) by the thickness (T) of the big end. S  As an example, assume that the length of the slope is 10 inches and the thickness is 4 inches. The mechanical advantage is equal to 10/4 or 2 1/2. As with the inclined plane, the mechanical advantage gained by using a wedge requires a corresponding increase in distance. T

Sample Questions

Screw  Turns rotation into lengthwise movement  Takes many twists to go a short distance  Holds things together  Examples: screws, bolts, clamps, jar lids, car jack, spinning stools, spiral staircases

Screw The mechanical advantage of an screw can be calculated by dividing the circumference by the pitch of the screw. Pitch equals 1/ number of turns per inch.

Sample Questions

Wheel and Axle  Makes it easy to move things by rolling them, and reducing friction  Examples: car, bicycle, office chair, wheel barrow, shopping cart, hand truck, roller skates

WHEEL AND AXEL  The axle is stuck rigidly to a large wheel. Fan blades are attached to the wheel. When the axel turns, the fan blades spin.

Wheel and Axel  The mechanical advantage of a wheel and axle is the ratio of the radius of the wheel to the radius of the axle.  In the wheel and axle illustrated above, the radius of the wheel is five times larger than the radius of the axle. Therefore, the mechanical advantage is 5:1 or 5.  The wheel and axle can also increase speed by applying the input force to the axle rather than a wheel. This increase is computed like mechanical advantage. This combination would increase the speed 5 times. 5 1

Sample Questions

GEARS-Wheel and Axel  Each gear in a series reverses the direction of rotation of the previous gear. The smaller gear will always turn faster than the larger gear.

Sample Questions

Pulleys  Pulley are wheels and axles with a groove around the outside  A pulley needs a rope, chain or belt around the groove to make it do work

Pulley  Makes lifting things with a rope easier by redirecting force and the addition of additional pulleys  Examples: flag pole, elevator, sails, fishing nets, clothes lines, cranes, window shades and blinds, rock climbing gear

Diagrams of Pulleys Fixed pulley: A fixed pulley changes the direction of a force; however, it does not create a mechanical advantage. Movable Pulley: The mechanical advantage of a moveable pulley is equal to the number of ropes that support the moveable pulley.

COMBINED PULLEY  The effort needed to lift the load is less than half the weight of the load.  The main disadvantage is it travels a very long distance.

Sample Questions

Summary Wedge Pushes material apart, cuts Wheel and Axle Makes it easy to move things by rolling them, and reducing friction Lever Helps lift heavy weights using longer distances Inclined Plane Makes it easier to move objects upward; a longer path, but easier lifting Screw Turns rotation into lengthwise movement Pulley Makes lifting heavy weights easier by redirecting force

Rube Goldberg Machines  Rube Goldberg machines are examples of complex machines.  All complex machines are made up of combinations of simple machines.  Rube Goldberg machines are usually a complicated combination of simple machines.  By studying the components of Rube Goldberg machines, we learn more about simple machines

When you slip on ice, your foot kicks paddle (A), lowering finger (B), snapping turtle (C) extends neck to bite finger, opening ice tongs (D) and dropping pillow (E), thus allowing you to fall on something soft. Safety Device for Walking on Icy Pavements

Squeeze Orange Juice Rube Goldberg Machine

WEB RESOURCES 1. Divinci's Machines 2. Edhead's 3. COSI applet 4. How a bicycle works