2. What it means to do workWhat it means to do work
WorkWork – force acting over a distance to– force acting over a distance to
move an objectmove an object
2 key points for work to be done2 key points for work to be done
An object has to moveAn object has to move
The object must move in the direction ofThe object must move in the direction of
the applied forcethe applied force
3. WorkWork
Work = Force x DistanceWork = Force x Distance
W = F x DW = F x D
UnitsUnits
Force = Newtons (kg m/sForce = Newtons (kg m/s22
) - N) - N
Distance = meters – mDistance = meters – m
Work = joules – J (N m)Work = joules – J (N m)
JouleJoule – unit of work and energy; 1– unit of work and energy; 1
newton-meternewton-meter
4. WorkWork
Example:Example:
If a weight lifter lifts a 800 N barbell aIf a weight lifter lifts a 800 N barbell a
distance of 2.5 m what is the work done?distance of 2.5 m what is the work done?
W = F x DW = F x D
800N x 2.5m800N x 2.5m
W = 2,000 JW = 2,000 J
6. PowerPower
PowerPower – the rate at which work is done,– the rate at which work is done,
or the amount of work per unit of timeor the amount of work per unit of time
Power = work/time p = w/tPower = work/time p = w/t
Power =Power = force x distanceforce x distance
timetime
7. PowerPower
Unit for power is called aUnit for power is called a watt (W)watt (W)
Watt is a joule/secWatt is a joule/sec
Ex: a 40 watt light bulb does work at a rateEx: a 40 watt light bulb does work at a rate
of 40 J/sof 40 J/s
Large quantities of power are measured inLarge quantities of power are measured in
kilowatts (kW)kilowatts (kW)
Horsepower (hp)Horsepower (hp) – used to rate electric– used to rate electric
motors and gas enginesmotors and gas engines
1 hp = 745.56 watts (746 watts)1 hp = 745.56 watts (746 watts)
9. Simple MachinesSimple Machines
Inclined planeInclined plane – a type of simple machine– a type of simple machine
that has a flat, slanted surface with nothat has a flat, slanted surface with no
moving partsmoving parts
The less slanted the surface, the longer theThe less slanted the surface, the longer the
distance over which the effort force is applieddistance over which the effort force is applied
IMA =IMA = effort distanceeffort distance == length of slopelength of slope == ll
resistance dist. height of slope hresistance dist. height of slope h
10. Simple MachinesSimple Machines
WedgeWedge – an inclined plane that moves– an inclined plane that moves
The greater the distance the wedge moves,The greater the distance the wedge moves,
the greater the force is on an objectthe greater the force is on an object
Calculating IMA of a wedge is the sameCalculating IMA of a wedge is the same
as an inclined plane (except use widthas an inclined plane (except use width
instead of height)instead of height)
11. Simple MachinesSimple Machines
ScrewScrew – an inclined plane wrapped– an inclined plane wrapped
around a cylinder to form a spiralaround a cylinder to form a spiral
Tight threads = longer distance over whichTight threads = longer distance over which
effort is exerted = easier to turneffort is exerted = easier to turn
Spaced threads = shorter distance overSpaced threads = shorter distance over
which force is exerted = harder to turnwhich force is exerted = harder to turn
12. Simple MachinesSimple Machines
LeverLever – a rigid bar that is free to pivot or– a rigid bar that is free to pivot or
turn about a fixed pointturn about a fixed point
FulcrumFulcrum – the fixed point– the fixed point
Effort armEffort arm – the part of the lever where– the part of the lever where
the effort force is appliedthe effort force is applied
Resistance armResistance arm – the part of the lever– the part of the lever
that exerts the resistance forcethat exerts the resistance force
13. LeversLevers
11stst
class lever R Eclass lever R E
Ex: scissorsEx: scissors
22ndnd
class lever R Eclass lever R E
Ex: wheelbarrowEx: wheelbarrow
33rdrd
class lever E Rclass lever E R
Ex: arm swingingEx: arm swinging
a hammera hammer
14. LeversLevers
IMA =IMA = length of effort arm___length of effort arm___ = _= _Le_Le_
length of resistance arm Lrlength of resistance arm Lr
Ex: A worker uses an iron bar to lift aEx: A worker uses an iron bar to lift a
manhole cover weighing 65 N. The effortmanhole cover weighing 65 N. The effort
arm of the lever is 60 cm long. What isarm of the lever is 60 cm long. What is
the IMA of the bar?the IMA of the bar?
IMA =IMA = 60cm60cm = 6= 6
10cm10cm
15. Simple MachinesSimple Machines
PulleyPulley – rope, chain, or belt– rope, chain, or belt
wrapped around a groovedwrapped around a grooved
wheelwheel
AA fixed pulleyfixed pulley is attached tois attached to
something that doesn’t movesomething that doesn’t move
(ceiling, wall, etc.)(ceiling, wall, etc.)
The IMA of a fixed pulley is 1The IMA of a fixed pulley is 1
AA movable pulleymovable pulley movesmoves
The IMA of a movable pulley is 2The IMA of a movable pulley is 2
16. PulleysPulleys
Block and tackleBlock and tackle
IMA can be multiplied by counting everyIMA can be multiplied by counting every
rope supplying an upward force on therope supplying an upward force on the
resistanceresistance
17. Simple MachinesSimple Machines
Wheel and axleWheel and axle – a simple machine– a simple machine
consisting of two wheels of differentconsisting of two wheels of different
sizes that rotate togethersizes that rotate together
IMA =IMA = radius of wheelradius of wheel == RwRw
radius of axle Raradius of axle Ra
