November 30, 2017 You need: Clean paper / pencil Work to turn in… “Using Machines” WS Warm Up: If I push against a wall (so hard that I’m sweaty and tired), was work done? Why or why not? I CAN: define work, power, and simple machines

Work and Power Dude! I need a raise

What is “Work”? When an object actually moves in the same direction as a force. The movement of Homer in the same direction as the force that pushed him means that some work was accomplished! Force

Formula for Work Work is measured in a unit called “Joules”

A push or pull can always be applied, but its not until we actually move it that the person did work on the object. Work Whe-hew This is FUN! Ungh! This is HARD WORK! Work is when a force moves an object If we apply a force of 100 N, but the object doesn’t move, how much work was done? 100 N x O m = ? W Think: If no movement occurs, was any work actually done? Force (Push) Distance Here’s the point: Work is what was actually accomplished!

Main Concept 1: Work is only done when the force and motion are in the same direction . The elevator is creating a force that moves the container up. The force and movement is the work that the elevator has accomplished.

I am here to pump you sissy's up! What is “Power”? I am here to pump you sissy's up! We like to think of Power as how strong someone is But in science we use “power” to say how long it takes to do a certain amount of work

Main Concept 2: Power is ONLY about how fast work gets done! More or Less Power? Main Concept 2: Power is ONLY about how fast work gets done! It’s nice to get work done quickly! So here we have a certain amount of stacked wood. We need to cut it! We have several choices of tools we can use: “Power Saw” This saw will get the work done eventually, but it takes way too long to do it Since this saw does the same work faster than the hand saw, we say it has MORE POWER!!! OR Hand Saw Here’s the point: Both will get the same work done (cutting all the boards), but one will take less time = more power!!!

Power is measured in a unit called “Watts” Formula for Power Power is measured in a unit called “Watts”

Power Gee … Isn’t he just mighty powerful? Ungh! Need… more… POWER! Once work is calculated, we simply see how much time we actually moved someone/something. Once we find our unit rate of how much work we did in 1 second, we’ve found out how much “Power” we exerted. Force (Push) Time [s] Distance

What is “Effort”? While there are more technical definitions, we can think of effort as how hard it is to accomplish work. Usually, riding on a moving object takes less energy than walking the same distance. So, riding on a skateboard takes less effort to move than just walking. Which takes LESS effort to move with: Walking or Riding? Effort is really the whole point of this entire unit! Humans like things to be as easy as possible. So we want to learn how to do work with as little effort as possible!

Simple Machines (Making work easier…phew!)

Simple Machines Foldable 8 Simple Machine Notes 7 Lever 6 Pulley 5 Wheel & Axle 4 Wedge 3 Screw 2 Inclined Plane 1 Simple Machines Simple Machines By John Smith Line up your papers about 1-2 cm apart, so that you see “5, 6, 7, 8” along the bottom. Fold the papers over so you see all 8 numbers in a row.

Simple Machines Foldable 8 Simple Machine Notes 7 Lever 6 Pulley 5 Wheel & Axle 4 Wedge 3 Screw 2 Inclined Plane Draw & Describe: A sloped surface connecting a lower level to a higher level. Examples: A boat ramp, wheelchair ramp,propeller, ladder/stairs Simple Machines Foldable Use your textbook (pg. 716-727) & websites to research simple machines: On each tab, draw and describe that type of simple machine. Then give 2-3 examples.

What are MACHINES? Most people think of complex, technical, or electronic gadgets with motors…, but machines can be much SIMPLER. A machine is any device that lets you do WORK in an EASIER or BETTER way. Basically: Simple machines make work EASIER.

How do machines do work? Machines make work easier by changing 3 things about the FORCE you exert to do work: AMOUNT OF FORCE you exert DISTANCE over which you exert force DIRECTION in which you exert force

What are SIMPLE MACHINES? There are only 6 basic simple machines that make work easier: Inclined Plane Wedge Screw Lever Wheel & Axle Pulley

COMPOUND MACHINES Compound Machines – are made of combinations of two or more simple machines. For example, a simple can opener is a combination of 3 simple machines: Lever Wheel & axle Wedge

WORK & SIMPLE MACHINES Simple machines DON’T change the amount of WORK done! (They change the size, distance or direction of your FORCE!) WORK IN = WORK OUT* (*usually machines lose a bit of work due to FRICTION…)

INCLINED PLANE An inclined plane is a flat, sloped surface. It connects a lower level to a higher level. You use less force over a longer distance to raise a load to a higher level. Input Force Output Force

INCLINED PLANE: Examples Ramps (Boat ramps, wheelchair ramps) Propeller Ladders/Stairs

SCREW A screw has a “thread” or “groove” wrapped around a central cylinder. While turning, it converts a twisting force into a forward or backward force. Input Force Output Force

SCREW: Examples & Uses Screws can holds things together or lift materials. Screws Screw top lids for jars/bottles Light bulb Swivel stools/chairs

WEDGE A wedge has slanting slides that meet at an edge – it splits material apart. It changes force in one direction into a splitting force that acts at right angles to the blade. Input Force Output Force

WEDGE: Examples & Uses Ax, Knife, etc. Zippers Used in all cutting machines (to split materials apart)

WHEEL & AXLE The wheel is locked to the central axle – when one turns, so does the other one. A short powerful force at the axle, will move the wheel’s edge a long distance. A long motion at edge of wheel, moves the axle with great force. Output Force Input Force Output Force Input Force

WHEEL & AXLE: Examples & Uses Screwdriver Windmill Cars/Bicycles Rolling Pin Door Knob Fan

PULLEY A pulley is a grooved wheel with a rope, used to raise/lower/move a load. Pulley systems change the direction and/or decrease the input force so you can move heavier loads. Output Force Input Force Output Force Input Force

PULLEY: Examples & Uses Cranes Raising a flag on a pole Window Blinds Raising a sail on a boat Clothesline

LEVER A lever is a bar that pivots or rotates on a point (called a fulcrum). Levers may change the size, distance or direction of the force.

LEVERS: Examples & Uses First Class Levers: Scissors, See-saws, Pliers Second Class Levers: Staplers, Nutcrackers, Wheelbarrows Third Class Levers Shovels, baseball bats, tweezers

Machines make work easier by changing 3 things about the FORCE: The amount of force The distance of the force The direction of the force

Machines make work easier by changing 3 things about the FORCE: The amount of force (eg. A ramp lets you lift a heavy object with LESS force)

Machines make work easier by changing 3 things about the FORCE: The distance of the force (eg. A baseball bat lets you move your arms a short distance, but move the end of the bat a large distance).

Machines make work easier by changing 3 things about the FORCE: The direction of the force (eg. The pulley on a set of window blinds lets you move the blinds UP with a DOWNWARD pull.

How do machines make work easier? In your science notebook, write the following questions: When you add pulleys to a system what happens to the force you need to do work? How can we change a lever to make it easier to lift a heavy weight?

What is the mechanical advantage of a machine? A machine’s mechanical advantage is the number of times a machine increases a force exerted on it. Mechanical = Output Force Advantage Input Force

What is the mechanical advantage of a machine? You exert 10 N of force on a can opener. The can opener exerts 30 N of force on the can. What is the mechanical advantage? Mechanical = Output Force = 30 N Advantage Input Force 10 N Mechanical Advantage = 3

What is the efficiency of a machine? The EFFICIENCY compares: the work you put IN to the work the machine puts OUT. An IDEAL machine is 100% efficient. INPUT WORK = OUTPUT WORK In the real world, some input work is always lost due to FRICTION between the moving parts of the machine.

What is the efficiency of a machine? EFFICIENCY = Output Work x 100% Input Work You mow the lawn with a rusty lawn mower. You do 50,000 J of work on the lawn mower but only 25,000 J go to cutting the lawn. What is the efficiency of the lawn mower?

What is the efficiency of a machine? You mow the lawn with a rusty lawn mower. You do 50,000 J of work on the lawn mower but only 25,000 J go to cutting the lawn. What is the efficiency of the lawn mower? EFFICIENCY = Output Work x 100% Input Work Efficiency = 25,000 J x 100% 50,000 J Efficiency = 50%

Try the rest of the practice problems on your own… Mechanical = Output Force Advantage Input Force EFFICIENCY = Output Work x 100% Input Work