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Machines - Ch. 7. I. Introduction to Machines (p.180-183) Machines Force Work Mechanical Advantage. A. Machines. Machine device that makes work easier changes the size and/or direction of the exerted force. B. Force. Effort Force (F e ) force applied to the machine

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machines ch 7

Machines - Ch. 7

I. Introduction to Machines

(p.180-183)

Machines

Force

Work

Mechanical Advantage

a machines
A. Machines
  • Machine
    • device that makes work easier
    • changes the size and/or direction of the exerted force
b force
B. Force
  • Effort Force (Fe)
    • force applied to the machine
    • “what you do”
  • Resistance Force (Fr)
    • force applied by the machine
    • “what the machine does”
c work
C. Work
  • Work Input (Win)
    • work done on a machine

Win = Fe × de

  • Work Output (Wout)
    • work done by a machine

Wout = Fr × dr

c work5
C. Work
  • Conservation of Energy
    • can never get more work out than you put in
    • trade-off between force and distance

Win = Wout

Fe × de = Fr × dr

c work6
C. Work
  • In an ideal machine...

Win = Wout

  • But in the real world…
    • some energy is lost as friction

Win > Wout

d mechanical advantage
D. Mechanical Advantage
  • Mechanical Advantage (MA)
    • number of times a machine increases the effort force
  • MA > 1 : force is increased
  • MA < 1 : distance is increased
  • MA = 1 : only direction is changed
d mechanical advantage8

Fr

Fe

MA

D. Mechanical Advantage
  • A worker applies an effort force of 20 N to open a window with a resistance force of 500 N. What is the crowbar’s MA?

GIVEN:

Fe = 20 N

Fr = 500 N

MA = ?

WORK:

MA = Fr ÷ Fe

MA = (500 N) ÷ (20 N)

MA = 25

d mechanical advantage9

Fr

Fe

MA

D. Mechanical Advantage
  • Find the effort force needed to lift a 2000 N rock using a jack with a mechanical advantage of 10.

GIVEN:

Fe = ?

Fr = 2000 N

MA = 10

WORK:

Fe = Fr ÷ MA

Fe = (2000 N) ÷ (10)

Fe = 200 N