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Simple Machines

- Device that makes doing work easier is a machine
- Machines increase applied force and/or change

direction of applied force to make work easier

Effort and Resistance

- Force applied to machine is effort force
- Resistance force force applied by machine to

overcome resistance

Energy and Simple Machines

- Amount of energy the machine transfers to the

object cannot be greater than the amount of

energy transferred to the machine

Energy and Simple Machines

- An ideal machine with no friction would have the

same input work and output work - Some energy transferred is changed to heat due to

friction

Mechanical Advantage

- The number of times a machine multiplies the

effort force.

Efficiency

- Measure of how much of the work put into a

machine is changed into useful output work by the

machine.

Lever

- Bar that is free to pivot about a fixed point

called the fulcrum

- MA of lever
- depends on the
- placement of
- the fulcrum

Simple Machines

Which lever will allow the weight to be lifted

with the least amount of force?

It is easier to lift a weight when the fulcrum is

closer to the weight being lifted.

Simple Machines

Below is a picture of a perfectly balanced

system. Describe how mass affects the distance

from the fulcrum.

200 g

100 g

The greater mass is closer to the fulcrum.

Notice that is twice as big and half as close. We

always measure to the center of mass.

Pulley

- Grooved wheel with a rope or cable running along

a groove

The greater the number of times the cable wraps

around the pulleys, the greater the MA.

Simple Machines

Which pulley system will allow the weight to be

lifted with the least amount of force?

Moveable pulleys, often grouped together in block

and tackle systems, reduce the amount of force

needed to lift an object.

Block and Tackle

Wheel and axle

- Machine with two wheels of different sizes

rotating together

Simple Machines

Gears are a type of simple machine. While it

takes less force to spin the larger wheel, the

smaller wheel spins at a faster rate.

Inclined Plane

- Sloping surface that reduces the amount of force

required to do work

Simple Machines

Which ramp would it be easiest to slide a box up

to the given height?

Making ramps longer lowers the amount of force

needed to move an object up the ramp.

Wedge

- Inclined plane with one or two sloping sides

Screw

- Inclined plane wrapped in a spiral around a

cylindrical post

Compound machine

- Uses a combination of two or more simple machines

Efficiency

The efficiency of machines can be determined by

using a simple formula found on the formula chart.

Machines are always less than 100 efficient

because of the force that opposes motion between

the parts of the machine. What force is it that

opposes this motion?

Friction opposes the motion in the machines.

Friction converts the machines work into heat.

Formulas

Vf Vi at d Vi t ½ at2 2ad Vf2

Vi2 d ½ (Vf Vi) t

W F x d

P Work/t

KE ½mv2

GPE mgh

ME KE PE