Chapter Chapter

machinesmachines

Machines

A device used to multiply forces

or simply to change the direction of forces

Components of MachinesLever…a bar that is free to

pivot, or turn, about a fixed pointFulcrum….Fixed point of the

LeverEffort Arm….Part of lever on

which the effort force is applied Resistance arm…. Part of the

lever that exerts the resistance force

Type I or First Class Lever

The fulcrum between the force and the load, or between input and output.

Type II or Second Class LeverReverse the position of the load

and the fulcrum. The load is in between the

fulcrum and the effort force.

Type III or Third Class LeverFulcrum is at one end the load is

at the other end….Input force is applied between them

Machines

Fulcrum MgWork = FD = Nd

D

d

M

N

F

Pulley

A Kind of a lever that can be used to change the direction of a force.

Mechanical advantage

The ratio of resistance force to effort force

MA = Fr/Fe

Fe….effort force

Fr…..resistance force

Ideal Mechanical advantage

Workout = Workin

Frdr = Fede

IMA = de/dr

Efficiency

Workout = Workin

efficiency = wo/ Wi X 100%

Compound MachinesConsists of two or more simple

machines linked…..so that the resistance force of one

machine………becomes the effort force of the

second.

Rube-Goldberg

Machines - An Application of Energy Conservation

If there is no mechanical energy losses then for a simple machine...

work input = work output

(F d)input = (F d)output

Examples - levers and tire jacks

Efficiency

Useful energy becomes wasted energy with inefficiency.

Heat is the graveyard of useful energy.

usedenergy

donework fficiencyE

Comparison of Kinetic Energy and Momentum

Kinetic energy is a scalar quantity.

Momentum is a vector quantity.

Discuss rubber bullets as compared to lead bullets.

Example Questions

A 10 lb weight is lifted 5 ft. A 20 lb weight is lifted 2.5 ft. Which lifting required the most work?

(a) 10 lb weight(b) 20 lb weight(c) same work for each lifting(d) not enough information is given to work

the problem

(c) same work for each lifting(c) same work for each lifting

An object of mass 6 kg is traveling at a velocity of 30 m/s. How much total work was required to obtain this velocity starting from a position of rest?

(a) 180 Joules

(b) 2700 Joules

(c) 36 Joules

(d) 5 Joules

(e) 180 N

(b) 2700 Joules(b) 2700 Joules

A 20 Newton weight is lifted 4 meters. The change in potential energy of the weight in Newton.meters is

(a) 20

(b) 24

(c) 16

(d) 80

(e) 5

(d) 80(d) 80