April 30 2015 You need Clean paper pencil

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

R v e w ie Work & Power

w What is WORK? e i R v e 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…. n If you haven’t exerted a force AND moved an object some distance, you haven’t done any WORK at all! n

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

Calculating WORK w ie v WORK = FORCE x DISTANCE e R Work Force = Distance F W Work Distance = Force D

w Calculating WORK e i R v e 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 = 30 N x 3 meters WORK = 90 N·m (90 J) Work is measured in Joules (J) 1 Joule = 1 N·m n

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

w Calculating POWER e i R v e 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 Power = 2, 000 N x 8 m = 16, 000 J 4 s 4 s Power = 4, 000 J/s (4, 000 Watts) n

Work w and Power Practice e i Problems v e R 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 n

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

Work and Power Practice w e i Problems v e R 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 Power = 300 N x 400 m= 120, 000 J 120 s Power = 1, 000 J/s (1, 000 Watts) n

w e Simple Machines i v e R work easier…phew!) (Making o e 9 d i v n i m

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

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

w What are MACHINES? e i R n n n v e 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.

R v e w ie

w machines do work? Howiedo R n v e Machines make work easier by changing 3 things about the FORCE you exert to do work: v v v AMOUNT OF FORCE you exert DISTANCE over which you exert force DIRECTION in which you exert force

w SIMPLE MACHINES? Whatieare R v e n There are only 6 basic simple machines that make work easier: • Inclined Plane • Wedge • Screw • Lever • Wheel & Axle • Pulley

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

w WORK & SIMPLE MACHINES e i R n v e 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…)

R n n w INCLINED PLANE e i v e 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: w e i Examples v e R Ramps (Boat ramps, wheelchair ramps) n Propeller n Ladders/Stairs n

w SCREW ie R n n v e 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. Output Force Input Force

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

w WEDGE ie R n n v e 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: w e i Examples & Uses v e R Ax, Knife, etc. n Zippers n n Used in all cutting machines (to split materials apart)

w WHEEL & AXLE e i R n n n v e 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

WHEEL & AXLE: w e i Examples & Uses v e R Screwdriver n Windmill n Cars/Bicycles n Rolling Pin n Door Knob n Fan n

w PULLEY ie v e R A pulley is a grooved wheel with a rope, n n 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

PULLEY: w e i Examples & Uses v e R Cranes n Raising a flag on a pole n Window Blinds n Raising a sail on a boat n Clothesline n

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

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

Machines make work easier by w e i changing v 3 things about the FORCE: e R n The amount of force n The distance of the force n The direction of the force

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

Machines make work easier by w e i changing v 3 things about the FORCE: e R n 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 w e i changing v 3 things about the FORCE: e R n 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? n. A machine’s mechanical advantage is the number of times a machine increases a force exerted on it. n 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. n An IDEAL machine is 100% efficient. n INPUT WORK = OUTPUT WORK n 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