1. 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

4. Work and Power
Dude! I need a raise

5. 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

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

7. 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!

8. 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.

9. 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

10. 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!!!

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

12. 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

13. 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!

14. Simple Machines (Making work easier…phew!)

15. 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.

16. 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 ) & websites to research simple machines:
On each tab, draw and describe that type of simple machine.
Then give 2-3 examples.

17. 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.

18. 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

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

20. 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

21. 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…)

22. 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

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

24. 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

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

26. 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

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

28. 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

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

30. 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

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

32. 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.

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

34. 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

35. 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)

36. 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).

37. 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.

38. 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?

39. 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

40. 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 N
Mechanical Advantage = 3

41. 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.

42. 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?

43. 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%

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