Chapter 7 AWork and Mechanical Advantage Calculating Mechanical

Chapter 7 AWork and Mechanical Advantage

Calculating Mechanical Work • What is work? • We will focus on Mechanical Work • When a force acts on an object to move it • 2 factors: force and displacement

Calculating Mechanical Work • Formula: W = Fd • Work = force x distance (displacement) • If no movement, no work • Pushing on a wall? No work

Machines

Really complex machines

Machines from science fiction ? Not quite there yet…. Exoskeleton

Simple Machines • What is a simple machine? • A tool made of basic mechanical parts • 3 types: • Levers • Wheels and axels • Inclined planes

Levers

Wheels and Axels

Inclined Planes

Using Simple Machines to Solve Problems • W=F x d • Unit for work is Joules (J) • What is the work done by a pulley that raises a 2490 N weight 53 m? • F= 2490 N • d= 53 m • W=Fd=(2490)(53)= 131, 000 N*m • W= 130, 000 J

Power • Quick note: • Power (P) is the rate of doing work • P = (W) / △t • W = work in Joules • △t = time in seconds • P is measured in watt (W)

Power • It takes 40 minutes to raise the weight before. How much power is needed? • P = (W)/△t • W = 131, 000 J • △t = 40 min * 60 sec/ min = 2400 s • P = (131, 000)/(240) = 54. 583333 J/s • P = 55 W

Simple Machines and Efficiency • What is The First Law of Thermodynamics? • Cannot create or destroy energy • No machine can create energy, only use energy you put in • But!!! Never 100% • Efficiency = (work that comes out) x 100% (work that goes in) Efficiency = (Wout)/(Win) x 100%

Mechanical Advantage and the Distance Principle • Machine make work easier • We need to give less force • Quick vocab: • Load/ resistance: system to be moved • Resistance force (Fr) = force needed to begin moving • Effort Force (Fe) = force actually exerted on the simple machine (or just effort)

Mechanical Advantage and the Distance Principle • Simple machines give you a mechanical advantage (MA) • Reduces the effort needed to do a certain amount of work • Does NOT reduce the amount of work needed • MA = weight/ effort

Mechanical Advantage and the Distance Principle • Note: we will always ignore friction in this book, so we are calculating ideal MA (IMA), not actual MA (AMA)

Mechanical Advantage and the Distance Principle • To conserve work & energy, simple machines use smaller force over a longer distance • Distance principle

Vocabulary quiz on Wednesday • Mechanical Work • Simple machines • Power • Watt • Load • Resistance force • Effort force • Mechanical advantage • Distance principle W=F x d