Physical SciencePhysical Science
Work & MachinesWork & Machines
What is Work?What is Work? WorkWork is is forceforce exerted on an object that exerted on an object that
causes the object to move some causes the object to move some distancedistance Force without moving a distance yields NO Force without moving a distance yields NO
WORK!!WORK!!
Work = Force x DistanceSI Unit for work is the Joule1 Joule = 1Newton x 1 Meter
Word ProblemsWord Problems Word problems can be confusing; but w/ some practice Word problems can be confusing; but w/ some practice
they’re not that bad. Here are a few hints to make them they’re not that bad. Here are a few hints to make them easiereasier 1. Be sure you remember the “Need-to-Know” formulas1. Be sure you remember the “Need-to-Know” formulas
S =d/t ; S =d/t ; A = VA = Vff – V – Vii ; F = MA ; W=FxD; Power = Work/Time ; F = MA ; W=FxD; Power = Work/Time
Time Time In the word problem be sure you know the units for each of the In the word problem be sure you know the units for each of the
variables in the particular formula being discussed.variables in the particular formula being discussed. Distance – Meter; Force – Newton; Volume - cmDistance – Meter; Force – Newton; Volume - cm33 or Liter or Liter
2. In the word problem, all but one of the variables is told to 2. In the word problem, all but one of the variables is told to you in one way or another. Identify what variable is being you in one way or another. Identify what variable is being asked to solve, then plug in the remaining variables to the asked to solve, then plug in the remaining variables to the formulaformula
Solve it!! Make sure you also keep track of the unitsSolve it!! Make sure you also keep track of the units
How much work performed:How much work performed: How much work is performed if you apply How much work is performed if you apply 85 newtons 85 newtons of force on a box of force on a box
causing it to move causing it to move 3 meters3 meters::
W = F x DW = F x D
W = 85N x 3m = 255 NmW = 85N x 3m = 255 Nm
255 J = 255 Nm255 J = 255 Nm How much work is performed if you apply How much work is performed if you apply 37 newtons 37 newtons of force and of force and
move a wagon move a wagon 4.3 meters4.3 meters??
W = F x DW = F x D
W = 37N x 4.3m = 159.1 NmW = 37N x 4.3m = 159.1 Nm
159.1 J = 159.1 Nm159.1 J = 159.1 Nm How much work is performed if you apply How much work is performed if you apply 118 newtons 118 newtons of force on a of force on a
car that is stuck in the mud and car that is stuck in the mud and doesn’t movedoesn’t move?:?:
W = F x DW = F x D
W = 118N x 0m = 0 NmW = 118N x 0m = 0 Nm
0J =0Nm 0J =0Nm You might be tired from pushing but no work was done!!You might be tired from pushing but no work was done!!
How much force required:How much force required:
How much force was required to move How much force was required to move an object 3 meters if 75 Joules of work an object 3 meters if 75 Joules of work were expended?were expended? Formula: Formula: Work = Force x DistanceWork = Force x Distance Need to solve for Force, w= 75 J & Need to solve for Force, w= 75 J &
D=3MD=3M
75 J = F x 3M75 J = F x 3M
75 NM / 3M = F75 NM / 3M = F
75 NM / 3M = F75 NM / 3M = F
25N = F25N = F
What is a What is a MachineMachine?? A device that makes A device that makes work easier work easier or or more effectivemore effective A machine makes work easier by changing the A machine makes work easier by changing the amount of amount of
forceforce, the , the distance covered distance covered or by changing the or by changing the direction of direction of the forcethe force
Mechanical AdvantageMechanical Advantage A machine’s A machine’s mechanical advantage mechanical advantage is the number of times a is the number of times a
force exerted on a machine is force exerted on a machine is multiplied.multiplied. Ideal Mechanical Advantage has no units ( they Ideal Mechanical Advantage has no units ( they
cancel each other out when doing the math cancel each other out when doing the math problemproblem
IMA = output force / input forceIMA = output force / input force
Efficiency of a MachineEfficiency of a Machine The amount of work obtained from a machine is always less The amount of work obtained from a machine is always less
than the amount of work put into it. This is because work is than the amount of work put into it. This is because work is lost to friction.lost to friction.
Efficiency = output work / input work x 100Efficiency = output work / input work x 100
Remember that work = force x distance
Simple MachinesSimple Machines
Inclined PlaneInclined Plane A plane is a flat surface. When that plane is inclined, or slanted, it can A plane is a flat surface. When that plane is inclined, or slanted, it can
help you move objects across distances. And, that's work! A common help you move objects across distances. And, that's work! A common inclined plane is a ramp. Lifting a heavy box onto a loading dock is much inclined plane is a ramp. Lifting a heavy box onto a loading dock is much easier if you slide the box up a ramp--a simple machine.easier if you slide the box up a ramp--a simple machine.
IMA = length of incline / height of incline
WedgeWedge you can use the edge of an inclined plane to push things apart. Then, the you can use the edge of an inclined plane to push things apart. Then, the
inclined plane is a wedge. So, a wedge is actually a kind of inclined plane. inclined plane is a wedge. So, a wedge is actually a kind of inclined plane. An axe blade is a wedge. Think of the edge of the blade. It's the edge of a An axe blade is a wedge. Think of the edge of the blade. It's the edge of a smooth slanted surface. smooth slanted surface.
ScrewScrew an inclined plane wrapped
around a cylinder A screw can convert a rotational
force (torque) to a linear force and vice versa.
LeverLever Any tool that pries something loose is a Any tool that pries something loose is a
lever. A lever is a rigid bar that "pivots" (or lever. A lever is a rigid bar that "pivots" (or turns) against a "fulcrum" (or a fixed point). turns) against a "fulcrum" (or a fixed point).
IMA = Distance from input force to fulcrum / distance from output force to fulcrum
11stst Class Levers Class Levers Notice howNotice how
The input & output forces are in opposite directions The input & output forces are in opposite directions The fulcrum is between the input & output forcesThe fulcrum is between the input & output forces
Examples include nail remover, paint can opener Examples include nail remover, paint can opener scissors, seesawscissors, seesaw
22ndnd Class Levers Class Levers Notice how:Notice how:
The input & output forces The input & output forces are in the same directionare in the same direction
Input force is farther Input force is farther away from the fulcrum away from the fulcrum than the output forcethan the output force
Examples include: wheel Examples include: wheel barrow, door, nutcrackerbarrow, door, nutcracker
33rdrd Class Lever Class Lever Notice how:Notice how:
The input & output The input & output forces are in the same forces are in the same directiondirection
The input force is closer The input force is closer to the fulcrum than the to the fulcrum than the output forceoutput force
Examples include rake, Examples include rake, shovel, baseball bat shovel, baseball bat and fishing poleand fishing pole
What Class of Lever?What Class of Lever?
1
76
45
3
2
8
1. _______ 2. _______ 3. _______ 4. _______
5. _______ 6. _______ 7. _______ 8. _______
1. 3rd Class 2. 1st Class 3. 1st Class 4. 2nd Class
5. 2nd Class 6. 3rd Class 7. 1st Class 8. 2nd Class
Wheel and AxleWheel and Axle two circular objects attached together about a two circular objects attached together about a
common axiscommon axis Wheel is the large cylinderWheel is the large cylinder Axle is the small cylinderAxle is the small cylinder
IMA = Radius of the wheel / Radius of the axle
PulleyPulley In a pulley, a cord wraps around a wheel. As the wheel In a pulley, a cord wraps around a wheel. As the wheel
rotates, the cord moves in either direction. Now, attach rotates, the cord moves in either direction. Now, attach a hook to the cord, and you can use the wheel's a hook to the cord, and you can use the wheel's rotation to raise and lower objects.rotation to raise and lower objects.
IMA of a pulley system = the number of ropes that IMA of a pulley system = the number of ropes that support the weight of the objectsupport the weight of the object
