Machine – device that makes work easier

B. Work – when an object moves in the same direction

as the force applied

Work = Force x Distance

Unit: Joule (J) or NewtonMeter (Nm)

Using a ramp (simple machine) makes it easier for April to move the speaker onto the stage.

C. Power – measures how fast you can do work

Power = Work / Time

Unit: Watt (W)

When April lifts a trumpet or a tuba up the stairs, she does work.

Power equals the amount of work done on an object in a unit of time. How much time would it take April to move her boxes upstairs if she runs?

D. How does a machine make work easier?

1) They change the amount of the force applied.

2) They change the direction of the force applied.

E. Mechanical Advantage

Measures how much easier a machine makes work

1) Input (Effort) Force:

Force exerted by a person on the machine.

2) Output (Resistance) Force

Force exerted by the machine on the object.

3) Draw the pulley below.

Input force Output

Force

4) Mechanical Advantage =

Output Force

_________________

Input Force

Drums are tuned by tightening and loosening bolts. Drum keys make the bolts easier to turn.

Which one would be best to play seesaw?

Efficiency: measures how effective a machine is

Work output x 100Work input

Ideal Machine = 100% efficient ** meaning you get out what you put in**

Ideal machines (100% efficient) do NOT exist !

Because all machines waste some work overcoming friction

Simple Machine

Simple Machine: a device that does work with only one movement.

Using a machine does not mean that you do less work,

they make the work easier to do.

Simple Machines (6 types)

Lever, pulley, wheel and axis, inclined plane, screw,

wedge

Inclined plane (ramp)- a flat surface that slopes

upward

Inclined Plane

M.A. = length of slope Height

Calculate the mechanical advantage.

Calculate the mechanical advantage.

Which has higher M.A.?

Wedge – a triangular, V-shaped object

Wedge

M.A. = Length of Wedge Width of Wedge

Screw- inclined plane wrapped around a post

ScrewThe threads of a screw act like an inclined plane to increase the distance over which input force is exerted.

Levers – a bar that pivots at a fixed point

M.A. = Length of effort arm (Input arm)Length of resistance arm (Output arm)

Levers Mechanical Advantage

Levers

Which one gives you a greater M.A.?

Levers in the BodyLevers can be found throughout your body. In the last two panels of the diagram, where would the output force be? What is the class of lever for each part of the body?

Levers have the following:

Fulcrum – fixed pivot point

Effort arm – force is applied here

Resistance arm – exerts the force from the effort arm

Pulley – a rope or chain that wraps around a wheel

Pulleys

M.A. = number of sections of rope that support the object

1) What type of pulley is this?

2) What is the M.A. of this system?

Wheel and axle – a large wheel turns a smaller axle

Wheel and Axle

M.A. = radius wheel radius axle

10 cm

2 cm

Which one has a higher M.A.?

Simple Machines in SailboatsYou can find many simple machines on a sailboat. Where are the pulleys on the diagrams?

Simple Machines

You cannot get more work from a machine than you put into it.

Machines simply decrease your effort and make the work easier.

Simple Machines all do work the same way: by moving an object through a distance.

5) The higher the mechanical advantage, the Less the effort force is and therefore the better the machine is.

Compound Machine: two or more simple machines working together

6) M.A. = resistance force / effort force

= 6 / 2

= 3

Frivolous machines

Work – transfer of energy through motion

2 conditions for work to be done

Force must be applied

Object must move in direction of the force

Equations for Work:

Work = force x distance

W = F x d

Unit for Work = Joule (J)

Practice problemYou move a stove a distance of 30 meters. This

requires a force of 80 N. How much work did you do?

d = 30 mF = 80 NW= ?

W = F x d

= 80 N x 30 m

W = 2400 Nm or J