1. Chapter Three : work and simple machines

2. Lesson 1: Work and Power What is work?
Work is the transfer of ________to an object by a force that makes an object __________________ of the force.
Work is only being done while _______________
_______________________
You push makes your bike move= work is _______
You push on the bike and it does not move= ____ work is done

3. Calculating Work Work equation
Work (in ______) = _______(Newton) x ________ (meter)
W = Fd
A joule unit is equal to a _____________
The joule is the SI unit of _____ and _______
The distance is the distance the object moves while ______________________________

4. Factors That Affect Work
The work done on an object depends on the direction of the ______applied and the direction of _________
A force that acts in the direction of the motion __________________
Force and motion are in
the same direction
Multiply the force and
the distance

5. Lifting Objects _______your backpack requires you to do work
Backpack has _________ because of the gravity
To lift, you must pull with an upward force greater than the weight
The work done to lift any object is equal to the _______ of the object multiplied by the ____________it is lifted

6. Work and Energy Doing work on an object transfers energy to the object
Kinetic energy- ________________________
Figure 4 on page 90
Boy applies a force on the tray to make it move; ___________________
This work ____________energy to the tray
The added energy is the ____________ energy of the tray

7. Work and Energy Lifting an object also increases the object’s energy
______________________________(GPE)
Energy of the object increases as its __________ increases
Girl lifts the tray: did work on the tray
GPE __________and it ________kinetic energy as it moves _____________
Transferred energy to the tray which ___________ the tray’s ___________and _____________energy

8. What is power? Power is the ______________________________
More quickly=more ___________
Power (in _______) = ________(in joules) / _________(seconds)
P= W/t
The SI unit of power is the watt (______).
1 J/s = 1 W
Work transfers energy
Power is the rate at which _______ is transferred to an object

9. Find Power
A boy does 18 J of work in 2.0s on his backpack as he lifts it from a table. How much power did the boy use on the backpack?
______________________________________
A child pulls a wagon, doing 360 J of work in 8.0s. How much power is exerted?
_______________________________________

10. Lesson 2: Using Machines
What is a machine?
A machine is _________________________
_____________________________________
Snow shovel, scissors, watch
There are simple and complex machines
All machines make tasks _______but they______ ________________________________ required
Machines change the way in which the work is done

11. Input Force to Output Force
In order to use a machine, you must apply a force.
__________ force- force you apply to the object
Figure 6 on page 96- apply a force on the hammer
The machine changes the input force into an ______
_______________
Output force is on the nail
_________ force- the force the machine applies
For example, the hammer changes the input force to an output force that pulls the nail out of the board

12. Input Work to Output Work
Machines convert, or change, ______work to _______ work
input work, Win = (_______force x distance the machine ___________________of the input force)
The output work, Wout = (_______force x the distance the machine ___________________ of the output force)
Work is done when applying a force on something and making it move

13. Input Work to Output Work
For example: a pair of scissors
IDENTIFY THE INPUT FORCE AND THE OUTPUT FORCE:
You apply an _________force that moves the blades and does work
You have to ________the handles to make the blades move
The scissors ________________________
Output force

14. How do machines make work easier to do ?
Three ways: It can change…
__________________________________
General Rule: True for all machines
You apply a _______ force over a ________ distance
You apply a __________ force over a _________ distance

15. Change the Size of a Force
A ____________ is a machine
Make it easier by changing the ________ of the force from small to greater
When the output force is greater than the input force, the output force _____________________________________
Example: Figure 7

16. Change the Distance a Force Acts
Using a rake to gather leaves is an example of a machine that _______________ the distance over which a force acts.
The person’s hands move the top of the rake a ____________ distance
What force is person applying? ______________________
The other end sweeps through a ____________ distance
What force is the rake applying? ___________________
Makes it easier to rake leaves

17. Continued…
The force applied by the rake ____________ as the distance over the force acts (the output ___________) ____________
When the output force acts over a ________ distance than the input force, the output force is ______ than the input force.

18. Change the Direction of a Force
Example : a pulley in Figure 7 on page 97
As the free end of the rope is pulled down, the object tied to the other end of the rope is lifted up.
The machine changes the __________ of the applied force.
Equal ______and _________forces act over __________ distances.

19. What is mechanical advantage?
Most machines change the size of the force applied to them.
A machine’s mechanical advantage is the _____________________________________
_______________________________________
MA = Fout / Fin
Mechanical advantage = ________ force (in N) divided by ________ force (in N)

20. Continued… MA can be less than, equal to, or greater than 1
______________: output force > input force
Crowbar
______________: output force < input force
Rake
______________: output = input
Pulley

21. Continued…
The ideal mechanical advantage (IMA) is the mechanical advantage if ____________________.
Can machines operate at IMA?
_______, because __________________________.
Page 98: solve the practice problem

22. What is efficiency?
The output WORK done by a machine ___________________ the input WORK of the machine because of friction.
Friction converts some of the input work to _______________________.
The converted energy cannot be used to do work.

23. Continued…
The efficiency of a machine is the ratio of the output WORK to the input WORK.
Efficiency (%) = output work (in J) x 100%
input work (in J)
Output work = Wout
Input work = Win

24. Continued… Try practice problem on page 99!
Because output work is always less than input work, a machine’s efficiency is always less than ____________________.
Figure 8 on page 99
_____________a machine’s moving parts _____________ efficiency
Try practice problem on page 99!

25. Lesson 3: Simple Machines
What is a simple machine?
A simple machines do work ______________________
Six types:
_________________
________________________
__________________

26. Levers A lever is a simple machine _______________
______________________________________.
The fixed point about which a lever pivots is called a _____________.
Figure 10 (soda can)
Fulcrum: finger tab attaches to the can
________and ________forces act on opposite ends of fulcrum

27. Levers Input arm: _________________________________
Output arm: _______________________________
There are three types of levers
They differ in where the ________and ________forces are relative to the ___________

28. First-class Lever
The _________ is in between the input and output force
Direction of input and output are always _______

29. Second-class lever
__________force is in between the input force and the fulcrum
The output and input act in the ________ direction
Makes the output force ___ input force
Wheelbarrow
Nut cracker

30. Third-class Lever
The ________force is between the output force and the fulcrum
Output and input act in the _______direction
Output force _____ input force
Tweezers, rake, Broom

31. First-class Lever The location of the fulcrum determines the MA
MA of a first class lever __________
Greater than 1: input arm is _______ than the output arm
Output force is ________than the input force
Less than 1: input arm is ________ than the output
Output force is _______ than the input force
Equal to 1: input and output arms & forces are _______

32. Second-class Lever Output arm is _______than the input arm
Output force __________input force
The MA is always __________________
For all second-class levers

33. Third-class Lever Output arm is always ________ than the input arm
Output force ___________ input force
MA is always ________________
For all third-class levers

34. Levers in the Human Body
Body uses all three classes of levers to move
__________ provide the input force
Neck
Foot
Arm
Figure 12 on page 106

35. Neck First-class _________ : joint connecting spine and skull
Neck muscles provide the _______force
Output force is applied to the _______and helps support your head’s _________

36. Foot
When standing on your toes, the foot acts as a second- class lever
Ball of foot: ______
Input force: comes from the muscles on the _____________

37. Arm Third-class lever Elbow: _________
Input force: ________ located near the elbow (forearm muscle/ bicep)

38. Wheel and Axle Is an _________________________________
_______________________________________
Axle=shaft
Example: screwdriver
Handle- wheel because it has the _________ diameter
shaft=- axle attached to the _________
_______ the handle and the shaft rotate when the handle turns

39. Using a Wheel and Axle When you turn the screwdriver
_______force applied to the handle (wheel)
_______force applied to the _______by the screwdriver’s _______
The wheel is larger than the axle= ________________________
This makes the screw easier to turn instead of using your finger

40. Inclined Planes Is a _______________. Also known as a _____
Takes less _______ to move an object upward along a ramp than it does to lift the object straight up
Useful for moving _______________
Because of __________, no ramp operates at its ______________

41. Wedge A ______________________________
A type of inclined plane with one or two _______________________
Doorstop- has _________sloped side
The shape of the wedge gives the _______ forces a different direction than the _______ force
Example: teeth
How?

42. Screws Is an _________________________________
_______________________________________
The screw threads change the _______force to an __________ force
What’s input force? ___________________
The output force pulls the screw ___________________
Figure 16 on page 108

43. Pulleys A simple machine that is a ____________________
___________________________________________

44. Fixed Pulleys A fixed pulley only changes the ___________ of the force
Example: window blind
Cord passes through the fixed pulley (of the window frame)
MA= ___________________

45. Movable Pulleys & Pulley Systems
Can be attached to the object being lifted
Called a ___________________
Movable pulleys _____________the force needed to lift an object; distance the force acts over ________________
Pulley system
Combination of _______and ________pulleys that work together

46. MA of Pulleys
The MA is equal to the _______of sections of _____ pulling up on the object

47. Find the MA

48. What is a compound machine?
_____________ simple machines that operate together form a compound machine
Figure 18
Can opener
_________ -class lever to move the handle
___________________to turn the blade
____________to puncture the lid

49. Gears A gear is a____________________________
_______________________________________
Two or more gears form a compound machine
When they interlock, one gear causes the other to ___________
The direction of the gears ___________
Different _______= different _________

50. Gears Continued… Smaller gears rotate _________than larger gears
Amount of _______transmitted through the gears is affected by the ________
Input force applied to a larger gear is reduced when it is applied to a smaller gear