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April 30, 2015 You need: Clean paper / pencil Simple Machines foldable Warm Up: What is your favorite simple machine? Why?

Work & Power

What is WORK? If you put a lot of effort into doing something and are worn out at the end, you think you’ve done a lot of WORK, right? If you put a lot of effort into doing something and are worn out at the end, you think you’ve done a lot of WORK, right? Not necessarily…. Not necessarily…. If you haven’t exerted a force AND moved an object some distance, you haven’t done any WORK at all! If you haven’t exerted a force AND moved an object some distance, you haven’t done any WORK at all!

What is WORK? In scientific terms, you do WORK when you exert a FORCE that causes an object to move some DISTANCE in the SAME DIRECTION of the force. In scientific terms, you do WORK when you exert a FORCE that causes an object to move some DISTANCE in the SAME DIRECTION of the force. - Force and motion are in the SAME DIRECTION, so work is being done. - Force and motion are NOT in the same direction, so no work is being done. - Some force is in the direction of motion, but some is not.

Calculating WORK WORK = FORCE x DISTANCE WORK = FORCE x DISTANCE W FD Force = Work Distance Distance = Work Force

Calculating WORK You carry a baby that weighs 30 N upstairs to his room (3 meters above you). How much work is done? You carry a baby that weighs 30 N upstairs to his room (3 meters above you). How much work is done? WORK = FORCE X DISTANCE WORK = FORCE X DISTANCE WORK = 30 N x 3 meters WORK = 30 N x 3 meters WORK = 90 N·m (90 J) WORK = 90 N·m (90 J) Work is measured in Joules (J) 1 Joule = 1 N·m 1 Joule = 1 N·m

What is POWER? Power is the rate at which work is being done (or how much work is being done in a unit of time). Power is the rate at which work is being done (or how much work is being done in a unit of time). POWER = WORK ÷ TIME POWER = WORK ÷ TIME More power means less time to do the same work OR more work done in the same amount of time. More power means less time to do the same work OR more work done in the same amount of time. Power is measured in Watts (W). Power is measured in Watts (W).

Calculating POWER A motor exerts a force of 2,000 N to lift an elevator 8.0 m in 4.0 seconds. What is the power of the motor? A motor exerts a force of 2,000 N to lift an elevator 8.0 m in 4.0 seconds. What is the power of the motor? Power = Work = Force x Distance Time Time Time Time Power = 2,000N x 8 m 4 s Power = 4,000 J/s (4,000 Watts) = 16,000 J = 16,000 J 4 s 4 s

Work and Power Practice Problems John pushes a heavy box for 4 m with a constant force of 60 N. Then Alex lifts the box, which weighs 200 N, to a height of 1.5 m. Who did more work? John pushes a heavy box for 4 m with a constant force of 60 N. Then Alex lifts the box, which weighs 200 N, to a height of 1.5 m. Who did more work? Work = Force x Distance John’s Work = 60 N x 4 m = 240 joules Alex’s Work = 200 N x 1.5 m = 300 joules

Work and Power Practice Problems Carrie operates a forklift at the soda warehouse. The machine does 7,500 J of work to lift a pallet of soda 3m. How much did the soda weigh in Newtons? Carrie operates a forklift at the soda warehouse. The machine does 7,500 J of work to lift a pallet of soda 3m. How much did the soda weigh in Newtons? Force = Work ÷ Distance Force = 7500 J ÷ 3 m Force = 2500 N W FD

Work and Power Practice Problems A sled dog exerts a force of 300 N to pull the sled 400 meters in 120 seconds. What is the dog’s power? A sled dog exerts a force of 300 N to pull the sled 400 meters in 120 seconds. What is the dog’s power? Power = Work = Force x Distance Time Time Time Time Power = 300N x 400 m 120 s 120 s Power = 1,000 J/s (1,000 Watts) = 120,000 J = 120,000 J 120 s 120 s

Simple Machines (Making work easier…phew!)

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

Simple Machines Foldable Use your textbook (pg ) & websites to research simple machines: Use your textbook (pg ) & websites to research simple machines: On each tab, draw and describe that type of simple machine. On each tab, draw and describe that type of simple machine. Then give 2-3 examples. Then give 2-3 examples. 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

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

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

COMPOUND MACHINES COMPOUND MACHINES Compound Machines – are made of combinations of two or more simple 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: 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! Simple machines DON’T change the amount of WORK done! (They change the size, distance or direction of your FORCE!) WORK IN = WORK OUT* WORK IN = WORK OUT* (*usually machines lose a bit of work due to FRICTION…) (*usually machines lose a bit of work due to FRICTION…)

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

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

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

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

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

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

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

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

PULLEY A pulley is a grooved wheel with a rope, used to raise/lower/move a load. 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. 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 PULLEY: Examples & Uses Cranes Cranes Raising a flag on a pole Raising a flag on a pole Window Blinds Window Blinds Raising a sail on a boat Raising a sail on a boat Clothesline Clothesline

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

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

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

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

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. A machine’s mechanical advantage is the number of times a machine increases a force exerted on it. Mechanical = Output Force Advantage Input Force 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? 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? What is the efficiency of a machine? The EFFICIENCY compares: The EFFICIENCY compares: –the work you put IN to –the work the machine puts OUT. An IDEAL machine is 100% efficient. An IDEAL machine is 100% efficient. INPUT WORK = OUTPUT WORK INPUT WORK = OUTPUT WORK In the real world, some input work is always lost due to FRICTION between the moving parts of the machine. 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 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? 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? 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 Mechanical = Output Force Advantage Input Force EFFICIENCY = Output Work x 100% Input Work