Unit 6 - Simple Machines Notes

Simple Machines

  • Types of Simple Machines:

    • Inclined Plane

    • Lever

    • Wedge

    • Screw

    • Pulley

    • Wheel and Axle

Definition of a Machine

  • A machine is anything that helps make work easier.

Definition of Work

  • Work is done when a force moves an object or changes its position.

  • Key Concept: Holding an object requires effort but does not count as work since there is no movement.

  • Example: Raising the box requires both effort and movement, thus constitutes work.

Energy and Work

  • When work is done, energy is used up.

Work Formula

  • Formula:
    Work(W)=Force(F)imesDistance(d)Work (W) = Force (F) imes Distance (d)

  • Unit of Work: Joule (J)

Understanding Work with the Work Triangle

  • The work triangle gives a visual representation:

    • W=FimesdW = F imes d

    • F=WdF = \frac{W}{d}

    • d=WFd = \frac{W}{F}

Example Problem: Weightlifting

  • Question: A weightlifter raises weights of 2000 newtons from the floor to a height of 2 meters. How much work has been done?

  • Work Calculation:

    • W=Fimesd=2000extNimes2extm=4000extJW = F imes d = 2000 ext{ N} imes 2 ext{ m} = 4000 ext{ J}

Conditions for Work to Occur

  • For work to be done, the direction of the force must be the same as the direction of motion.

  • Example Question: If one pulls on a tree but the tree does not move, does any work get done?

Definition of Power

  • Power is the rate at which work is done, or it is the amount of work per unit of time.

Power Formula

  • Formula:
    Power(P)=Work(W)Time(t)Power (P) = \frac{Work (W)}{Time (t)}

Understanding Power with the Power Triangle

  • The power triangle provides relationships similar to the work triangle:

    • W=PimestW = P imes t

    • P=WtP = \frac{W}{t}

    • t=WPt = \frac{W}{P}

Example Problem: Calculating Power

  • Maxine's Power:

    • Maxine carries a box up 10 meters using a force of 20 newtons in 5 seconds.

    • Power Calculation:

    • Work done: W=Fimesd=20extNimes10extm=200extJW = F imes d = 20 ext{ N} imes 10 ext{ m} = 200 ext{ J}

    • Power: P=Wt=200extJ5exts=40extWP = \frac{W}{t} = \frac{200 ext{ J}}{5 ext{ s}} = 40 ext{ W}

  • Emily's Power:

    • Emily runs 50 meters in 7 seconds with a mass of 60 kg.

    • (Power calculation depends on established work based on force generated).

Important Notes

  • Always establish whether movement occurs to determine if work is done.

  • Energy and work are directly related; energy is consumed when work is performed.