Lever System

Sunday, November 3, 2013

Creating Our Own Pulley System

Our task was to work in a group and create a pulley system with a fixed and movable pulley.

We used a spring scale to measure the amount of force it took to lift the movable pulley and the weight we attached to it. It took .95 Newtons of force to lift it. Then using the pulley system we used the spring scale again to measure the amount of force needed to lift the movable pulley and weight. It took only .4 Newtons to lift the weight. The mechanical advantage is 2:1.

Activity 1.1.2 Simple Machines Practice Problems

We got to take a look at a few different real life problems using simple machines.

Simple Machines: Lever

EX 1:
       A first class lever, in static equilibrium, has a 50 lb resistance forces and 15 lb effort force. The lever's effort force is located 4 ft from the fulcrum.

1. Sketch and annotate lever system described above

2. Calculate:

Actual Mechanical Advantage (AMA)
AMA= Force Resistance/Force Effort
AMA= 50 lbs/15 lbs
AMA= 3.33

3. Static Equilibrium Calculations:

 DR= Distance of Resistance Force
 M= moment (Force x distance)
 Moment Effort + Moment Resistance
-->

∑

-->M_Fulcrum= 0

(15 lbs)(4 ft) + (50 lbs)(DR)= 0

50 lbs(DR) = 60 lbs/ft

DR= 1.2 ft

EX 2:
       A wheel barrow is used to lift a 200 lb load. The length from the wheel axle to the center of the load is 2 ft. The length from the wheel and axle to the effort is 5 ft.

1. Illustrate and annotate lever system described above

2. Calculate: 

Ideal Mechanical Advantage (IMA)
IMA= Distance(effort force)/Distance(resistant force)
IMA= 5 feet/ 2 feet
IMA= 2.5
3. Static Equilibrium Calculations: 

FE= Force of Effort Force 
M= moment (Force x distance)
 Moment Effort + Moment Resistance

∑ M_Fulcrum= 0

(200lbs)(2ft) + (5ft)(FE)= 0

5ft (FE) = 400 lbs/ft

FE= 80 lbs

EX 3:

       A medical technician uses a pair of 4 inch long tweezers to remove a wood sliver from a patient. The technician is applying 1 lb of squeezing force to the tweezers. If more than 1/5 lb of force is applied to the sliver, it will break and become difficult to remove.

1. Sketch and annotate lever system described above

2.  Calculate:

Actual Mechanical Advantage (AMA)
AMA= Force Resistance/Force Effort
AMA= 1 lb/ (1/5) lb
AMA= 0.2

3. Static Equilibrium Calculations:

DR= Distance of Effort Force
 M= moment (Force x distance)
 Moment Effort + Moment Resistance

∑ M_Fulcrum= 0

(4 in)(1/5 lb) + (1 lb)(DE)= 0

1 lb(DE) = (4/5) lb/in

DE= 0.8 in

Simple Machines: Pulley 

EX 1:

       A construction crew lifts approximately 560 lb of material several times during a day from a flatbed truck to a 32 ft rooftop. A block and tackle system with 50 lb of effort force is designed to lift the materials.

1. Calculate: 

Actual Mechanical Advantage (AMA)
AMA= Force Resistance/Force Effort
AMA= 560 lb/50 lb
AMA= 11.2

2. How many supporting strands will be needed in the pulley system?

2 x(# of moveable pulleys) + 1(if changing direction)= # of strands

(2 x 4) +1= 9 strands