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 MachinesWhich 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.

fulcrum fulcrum

Simple Machines

fulcrum

200 g100 g

Below is a picture of a perfectly balanced system. Describe how mass affects the

distance from the fulcrum.

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 MachinesWhich 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 MachinesWhich 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

EfficiencyThe 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 machine’s work into heat.

Formulas

W = F x d

Vf = Vi + at

d = Vi t + ½ at2

2ad = Vf2 – Vi2

d = ½ (Vf + Vi) t

KE = ½mv2

GPE = mgh

ME = KE + PE

P = Work/t