Chapter 15 Simple Machines. Two Types of Work Involved with Using a Machine Work Input = work that goes in (comes from the force that is applied to.

Chapter 15

Simple Machines

Two Types of Work Involved with Using a

Machine• Work Input = work that goes in (comes from the force that is applied to the machine)

Work Output = work that comes out (force that’s exerted by the machine)

Work is Conserved

• can never get out more than you put inin reality, the work output is always less than the work inputWhy? FRICTION

How Much Work isLost to Friction?• Efficiency = work

output + f work input

f = energy lost to frictionmachines are more efficient if we keep them clean & lubricated (WO ≈ WI)

Work is ConservedWork = F * d

• there can be a change in the forcethere can be a change in the distancenever both at the same time

Forces Involved• Effort force = what a

person puts into it

Resistance force = what you & the machine are working against (often the weight of the object being moved)

Mechanical Advantage• # of times a machine multiples the effort force (what you put in) to overcome the resistance force (usually the weight of the object you’re trying to move)

the greater the MA, the easier it is to complete the job

Inclined Plane•alters the way work is done, not the amount of work done

•the lower the slant, the longer the distance to push, the lower the effort force needed

•the MA increases as the slant of the plane decreases

Wedge•most are made of 2

inclined planes

•unlike the inclined plane, the wedge itself moves

•as the wedge moves a greater distance, it moves the object with greater force

Wedge•the longer & thinner the wedge, the less effort force required to overcome the resistance

•this is why we sharpen blades, knives, etc. – it also increases the MA

Screw•this is an inclined plane wrapped around a cylinder to form a spiral

•as the screw rotates, each turn moves the screw up or down a certain distance

Screw•the closer the threads or ridges are, the greater the distance over which the force is multipiled

•this means that you may have to work longer to cover that distance, but you will use less effort force

• Effort moves farther than resistance

• Multiplies effort force & changes its direction

•Effort moves farther than resistance

•Multiplies effort force but does not change its direction

•Resistance moves farther than effort

•Does not multiply force•Multiplies the distance the effort

force travels

Fixed Pulley

•does not multiply force

•changes direction of effort force

•MA = 1

Movable Pulley

• multiplies effort force

• cannot changes direction of effort force

• MA = effort distance

resistance distance