1. Work, Power & Simple Machines (Making work easier…phew!)

2. 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!

3. 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. Examples: Examples: – Pushing a lawn mower – Lifting books out of your bag – Pulling a suitcase on wheels

4. What 2 things must happen for WORK to be done? MOTION – The object must move. MOTION – The object must move. If the object doesn’t move, If the object doesn’t move, there is no work done. there is no work done. FORCE & MOTION IN THE SAME DIRECTION FORCE & MOTION IN THE SAME DIRECTION Movement must be in the same direction as force. Movement must be in the same direction as force. If the motion is in a different direction than the force, there is no work. If the motion is in a different direction than the force, there is no work.

5. Is WORK being done? Pushing a car that’s stuck in snow. Pushing a car that’s stuck in snow. NO! (No work because the car doesn’t move). Lifting a baby out of his stroller. Lifting a baby out of his stroller. YES! (Baby moves in same direction as you lift) Carrying your bookbag to class. Carrying your bookbag to class. NO! (Force is pulling up, but motion is sideways) Pushing a lawn mower. Pushing a lawn mower. YES! (Mower goes in same direction as you push)

6. Calculating WORK WORK = FORCE x DISTANCE WORK = FORCE x DISTANCE The greater the distance, the more you work. Eg. Pushing a car 100 m vs. Pushing a car 200 m (more work!) Pushing a car 200 m (more work!) The greater the force, the more you work. Eg. Lifting 1 book onto a table vs. Lifting 10 books onto a table (more work!) Lifting 10 books onto a table (more work!)

7. 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

8. 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).

9. POWER Think about 2 cars – one with a 200 horsepower engine, and one with a 500 horsepower engine. Think about 2 cars – one with a 200 horsepower engine, and one with a 500 horsepower engine. Which one has the more powerful engine? Which one has the more powerful engine? Which one will go further in 10 minutes? Which one will go further in 10 minutes? Which one will go 10 miles in the shortest amount of time? Which one will go 10 miles in the shortest amount of time?

10. 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

11. What are MACHINES? Most people think of complex, automated, technical, or electronic gadgets with motors…, but Most people think of complex, automated, 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 more effective way. A machine is any device that lets you do WORK in an easier or more effective way.

12. 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  DIRECTION in which you exert force

13. How do Machines work? How do Machines work? In other words, a machine changes the strength, distance, direction of your push or pull. In other words, a machine changes the strength, distance, direction of your push or pull.

14. What is the mechanical advantage of a machine? 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

15. What is the mechanical advantage of a machine? 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 = Output Force = 30 N Advantage Input Force 10 N Mechanical Advantage = 3 Mechanical Advantage = 3

16. What are SIMPLE MACHINES? There are only 6 basic kinds of simple machines that make work easier. There are only 6 basic kinds of simple machines that make work easier. These 6 simple machines make up all the other compound machines we use everyday. These 6 simple machines make up all the other compound machines we use everyday.

17. SIX SIMPLE MACHINES SIX SIMPLE MACHINES The six simple machines are: Inclined Plane Inclined Plane Wedge Wedge Screw Screw Lever Lever Wheel & Axle Wheel & Axle Pulley Pulley

18. INCLINED PLANE INCLINED PLANE An inclined plane is a flat, sloped surface connecting a lower level with a higher level. An inclined plane is a flat, sloped surface connecting a lower level with a higher level.

19. INCLINED PLANE INCLINED PLANE It lets you use less force over a longer distance to raise a load to a higher level. It lets you use less force over a longer distance to raise a load to a higher level. Input Force Output Force

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

21. WEDGE WEDGE A wedge has slanting slides that taper to a thin edge – it splits material apart. (A moving inclined plane!) A wedge has slanting slides that taper to a thin edge – it splits material apart. (A moving inclined plane!)

22. It converts motion in one direction, into a splitting motion that acts at right angles to the blade. It converts motion in one direction, into a splitting motion that acts at right angles to the blade. WEDGE WEDGE Input Force Output Force

23. 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) Lifting machines may use wedges to slide under loads Lifting machines may use wedges to slide under loads

24. SCREW SCREW A screw has a “thread” or “groove” wrapped around a central cylinder. (Another inclined plane - wrapped around a cylinder!) A screw has a “thread” or “groove” wrapped around a central cylinder. (Another inclined plane - wrapped around a cylinder!)

25. SCREW SCREW While turning, it converts a twisting motion into a forward or backward motion. While turning, it converts a twisting motion into a forward or backward motion. Input Force Output Force

26. 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

27. LEVER LEVER A lever is rigid bar that pivots/rotates on a fixed point. The fixed point is called the “fulcrum”. A lever is rigid bar that pivots/rotates on a fixed point. The fixed point is called the “fulcrum”.

28. LEVER LEVER Levers may increase the size or distance of force or change direction of the force. Levers may increase the size or distance of force or change direction of the force. There are 3 types of levers. There are 3 types of levers.

29. 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

30. WHEEL & AXLE A wheel and axle are 2 circles or cylinders attached together around a common axis. A wheel and axle are 2 circles or cylinders attached together around a common axis. The larger circle is the “wheel”, the smaller cylinder/rod is called the “axle”. The larger circle is the “wheel”, the smaller cylinder/rod is called the “axle”.

31. 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

32. 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

33. 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.

34. PULLEY PULLEY A simple fixed pulley only changes the direction of force. A simple fixed pulley only changes the direction of force. Pulley systems decreases the input force, allowing you to move heavier loads. Pulley systems decreases the input force, allowing you to move heavier loads. Output Force Input Force Output Force Input Force

35. 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

36. COMPOUND MACHINES COMPOUND MACHINES Most machines are combinations of 2 or more simple machines. Most machines are combinations of 2 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