PHYSICS: CHAPTER 4 NOTE PACKET Name:_____________________________________________
Chapter 4.1: Work and Machines
I. Work
What is ________________?
i. Work is done on an object when the ______________________________
____________________________________________________.
1. The object must move some _____________as a result of your
________.
2. Only the force acting ___________________________________ as the
object’s motion is performing work.
a. Fig. 2, page 109:
QUESTION: IF YOU PULL AN OBJECT HORIZONTALLY, WHAT PART OF YOUR FORCE DOES WORK?
_____________________________________________________________________________.
b. Calculating Work
i. The amount of work you do depends on both the _____________________
you exert and the ___________________________________________.
1. The amount of ______________ done on an object can be determined
by ________________________________ times
___________________:
a. WORK = __________________________________
b. SI Unit for WORK:
i. When force = _____________________________
ii. When distance = __________________________
1. The SI Unit = (N*m) or a ______________
iii. Ex:
1. How much work is performed if you move a 50 N
object .5m?
2. What if the object was 100 N?
QUESTION: WHAT IS THE SI UNIT FOR WORK? __________________________________.
c. POWER
i. Work is ___________________________________.
ii. Power is the ________________________________.
1. Power equals the ____________________________________ on an
object in a __________________________.
a. With _____________________, you can do the same amount of
__________ in_____________ time.
iii. Calculating Power
1. POWER = ____________________________
2. POWER = ______________________________
a. Ex:
i. A tow truck exerts a force of 11,000 N to pull a car out of
a ditch. It moves the car a distance of 5 m in 25 seconds.
What is the power of the tow truck? (Set Up, Substitute,
Solve).
iv. Power Units
1. When work is measured in joules and time in seconds, the SI unit of
power is the joule per second (J/s).
a. Also known as the ________________.
i. In honor of ___________________
1. Steam engine engineer.
b. One watt is a very small amount of power.
i. Power is more often expressed in a ________________.
1. ____________watts
a. One horsepower = _______________.
QUESTION: WHAT IS A KILOWATT? ______________________________________________.
Chapter 4.2: How Machines Do Work
I.
Notes:
a. What Is a Machine?
i. A device that allows you to ________________________________________.
ii. Input and Output Forces
1. Input Force
a. The force ____________________________ on the machine.
2. Output Forces
a. The force the machine _______________________________.
iii. Input and Output Work
1. Input Work
a. Input ________________ x Input __________________
2. Output Work
a. Output _________________ x Output ____________________
i. The amount of ____________ work can
______________________________ than the amount of
_______________ work.
iv. A machine makes work easier by ______________ at least one of _________
factors.
1. Change the ___________________________ you exert.
2. Change the____________________ over which you exert your force.
a. Exerting less force over a greater distance.
3. Change the ___________________ in which you exert your force.
a. Exerting the same force over the same distance, but in an
opposite direction.
QUESTION: How does the cable system on a weight machine make raising the weights
easier?
________________________________________________________________________
________________________________________________________________________
_______________________________________________________________________.
b. Mechanical Advantage (MA)
i. The ________________________________________________ exerted on it.
1. Mechanical Advantage = ______________ Force/____________ Force
a. Increasing Force
i. Output Force ________ Input Force
b. Increasing Distance
i. Output Force ________ Input Force
c. Changing Direction
i. Output Force ________ Input Force (no change in force)
c. Efficiency of Machines
ii. Input Work is _______________________________ than Output Work
1. Force must be applied to __________________________________ of
the machine itself
iii. Expressed as a percentage
1. To calculate the efficiency of a machine, ___________________ the
_________________________ by the ______________________ and
multiply the result by 100 percent.
a. Efficiency = __________________________________
iv. Real and Ideal Machines
1. ___________________________
a. Efficiency is _______________________________ 100%
i. loss due to friction
2. ___________________________
a. Efficiency is ____________________________
i. does not exist.
QUESTION: Why is output work always less than input work in real situations?
_____________________________________________________________________
Chapter 4 section 3 Notes : Six Simple Machines
Inclined Plane, Wedge, Screw, Wheel and Axle, Lever, Pulley
1. Inclined plane
• Also known as a _______________________ – a flat sloped surface.
A. How it works:
– Allows you to exert your force over a longer distance.
– Input force = ________________________________________________
– Output force = ________________________________________________inclined
plane
• Output force is ______________________to the objects weight
B. Inclined plane-Mechanical Advantage
• IMA = length of incline
Height of incline
Example: if you are loading a truck that is 1 meter high using a ramp that is 3 meters long, the IMA =
3m / 1m = 3
Therefore: the inclined plane increases the force you exert on the object by three times.
By increasing the __________________________________, the __________________ needed to
push or pull the object.
2. Wedge- A device that is _________________________________________________
• Instead of moving an object along an inclined plane, you move the inclined plane itself.
3. Screws- An inclined plane _____________________________
 The threads act like an ________________________ to increase the distance over which you
____________________.
 The threads exert an ____________________ on the wood, pulling the screw into the wood.
 The ______________between the wood and the screw holds the screw in place.

The closer the threads are the_________________ the mechanical average.
4. Levers-A rigid bar that is free to pivot, or rotate, on a fixed point.
• The fixed point that a lever pivots around is called a _________________
•
3 classes, based on location of _____________, ________________ (E) and
________________________ (load)(R)
A. First class lever
• Fulcrum is __________________ the effort force and the resistance
• Ex. Scissors, crowbar, car jack, prying the lid using a screw driver
B. Second class lever
• Fulcrum is at one end, effort is at the other end, the ___________________is in between
Ex. Wheelbarrow, a Door, a Nutcracker,
C. Third class lever
• Fulcrum is at one end , ______________ is close to fulcrum, resistance is at other end
• Almost all sports equipment ex.
• Golf club, baseball bat, lacrosse stick, fishing rod, rake, hockey stick etc.
Mechanical Advantage
• Ratio of the ____________________________________
•
•
IMA = ideal mechanical advantage, _______________________________
IMA Formula =
Effort arm distance (cms)
Resistance arm distance (cms)
Actual Mechanical Advantage
• Measures ratio of resistance force to effort force, __________________
•
Formula =
•
When MA is less than one the __________________________________
•
When the MA is greater than one the machine ________________________
Resistance Force(g)
Effort Force(g)
5. Wheel and Axle- a simple machine made of two circular or cylindrical objects fastened together
that rotate about a common axis
 The _____________________________________
 Example: screw driver
 It works because the wheel is larger than the axle; the axle rotates and exerts a large output
force.
 The greater the ratio between the radius of the wheel and the axle the greater the
___________________________.
6. Pulley- a simple machine made of a small grooved wheel and a rope or cable wrapped around it
 Pulley’s decrease the amount of input force needed to lift the object and it can change the
direction of the input force.
 Example: raising a flag pole.
 Two basic types:
A________________-pulley that is attached to a structure
B. __________________- pulley attached to a structure that can move
 The ideal mechanical advantage is equal to the number of sections of rope that support
the object
Others:
______________________- utilizes two or more simple machines
 Ex: Apple peeler, bicycle