The product of the force applied to an object and the distance through which the force was applied (Force*Distance=Work (w=f*d)
All or part of the force must act in the direction of the movement
Work does NOT involve time, only force and distance
No work is done when you stand in place holding an object.
1 newton-meter is a quantity known as a Joule
Named after British physicist James Prescott Joule
How quickly work is done
Amount of work done per unit time.
If two people mow two lawns of equal size and one does the job in half the time, the person who did it quicker did the same power, but they both did the same amount of work.
Power=Work/Time (P=W/T)
A unit named after Scottish inventor James Watt
Invented the steam engine
P=W/T
Joules/Second
1 watt = 1 J/s
Used to measure power of light bulbs and small appliances
An electric bill is measured in kW/hrs
Horsepower (hp) = 745.5 watts
Traditionally associated with engines. (car, motorcycle, lawn mower).
The term horsepower was developed to quantify power. A strong horse could move a 750N object one meter in one second.
Started as "this engine could do the amount of work 6 horses could
A device that makes work easier by changing the size, direction, or distance of a force
Input force (F_i): Force applied to a machine
Output force (F_o): Force applied by a machine
Work input:
Work done on a machine.
Input Force*Input Distance< (F_i*D_i=Input Force)
Work Output:
Work done by a machine.
Output Force*Output Distance (F_o*D_o=Output Force)
WORK OUTPUT CAN NOT BE GREATER THAN WORK INPUT
The number of times a machine multiplied the input force
MA=F_o/F_i
TWO TYPES: Ideal and Actual
IDEAL:
Involves no friction.
Is calculated differently for different machines
Usualy D_i/D_o
ACTUAL:
Involves Friction
Calculated the same for all machines
Efficiency can never be greater than 100% because of friction
Some work is always needed to overcome friction
A percentage comparison of W_o/W_i
The Lever:
its... its a lever... its just a bar that pivots...
Fulcrum=the pivot point of a lever
First Class Lever: the fulcrum is located between the effort and resistance.
Makes work easier by multiplying effect force AND changing direction
Ex: Teeter-Totter
Second Class Lever: Resistance is found between the fulcrum and input force
Makes work easier by multiplying the input force, but NOT changing direction.
Ex: A wheelbarrow
Third Class Lever: Input force is located between the output force and the fulcrum
Does NOT multiply input force, only multiplies the distance
Ex: A tennis racket
Mechanical Advantage of Lever
Ideal = input arm length/output arm length
input arm = distance from the input force to the fulcrum
Output arm = distance from output force to the fulcrum
Wheel and Axle:
A lever that rotates in a circle
A combination of 2 wheels of different sizes.
Smaller wheel is termed the axle
IMA = radius of wheel/radius of axle
The Inclined Plane:
A slanted surface used to raise an object
Ex: Ramps, stairs, ladders
IMA = length of ramp/height of ramp
Can never be less than one
The Wedge:
An inclined plane that moves
Ex: Knife, axe, razor blade
MA is increased by sharpening it
The Screw:
An inclined plane wrapped around a cylinder
The closer the threads, the greated the mechanical advantage
Ex: bolts, augers, drill bits
The Pully:
A chain, belt, or rope wrapped around a wheel
Can either change the direction or amount of effort force
Ex: flag pole, blinds, stage curtain
FIXED Pully
Can only change the direction of a force (MA=1)
MOVEABLE Pully
Can multiply an effort force, but cannot move direction. (MA>1)
IMA=number of supporting ropes
Compound machine:
A combination of 2 or more simple machine
Cannot get more work out of a compound machine than is put in