SlideServe
Télécharger Obtenir Pro
Menu
Accueil Pro
Préférences
ApparenceLight Aide et commentaires
© SlideServe · v2026

WORK 8.2

yan avatar
yan
21 diapositives · 458 Views · Jul 27, 2014

WORK 8.2. Chapter Eight: Work. 8.1 Work 8.2 Efficiency and Power. Chapter 8.2 Learning Goals. Describe the relationship between work and power. Apply a rule to determine the amount of power required to do work. Explain the meaning of efficiency in terms of input and output work.

#work 8.2 #work 8.2 ppt #powerpoint #presentation
WORK 8.2 - slide 1
01 / 21WORK 8.2
1 / 17

Télécharger la présentation

WORK 8.2
Une image / un lien ci-dessous est fourni (tel quel) pour télécharger la présentation

Politique de téléchargement : le contenu du site vous est fourni TEL QUEL pour votre information et votre usage personnel ; il ne peut être vendu, concédé sous licence ni partagé sur d’autres sites sans l’accord de son auteur.Le contenu vous est fourni TEL QUEL, pour votre information et votre usage personnel uniquement. Téléchargez la présentation en cliquant sur ce lien. Lors du téléchargement, si vous ne parvenez pas à télécharger une présentation, l’éditeur a peut-être supprimé le fichier de son serveur.Pendant le téléchargement, si vous ne parvenez pas à obtenir une présentation, le fichier a peut-être été supprimé par l’éditeur.

F I N

Plus de contenu associé

Transcription de la présentation

  1. WORK 8.2

  2. Chapter Eight: Work • 8.1 Work • 8.2 Efficiency and Power

  3. Chapter 8.2 Learning Goals • Describe the relationship between work and power. • Apply a rule to determine the amount of power required to do work. • Explain the meaning of efficiency in terms of input and output work.

  4. Key Question: How can a machine multiply forces? Investigation 8B Work

  5. 8.2 Efficiency and Power • Every process that is done by machines can be simplified in terms of work: • work input:the work or energy supplied to the process (or machine). • work output:the work or energy that comes out of the process (or machine).

  6. 8.2 Efficiency and Power • A rope and pulley machine illustrates a rule that is true for all processes that transform energy. • The total energy or work output can never be greater than the total energy or work input.

  7. 8.2 Efficiency • 65% of the energy in gasoline is converted to heat. • As far as moving the car goes, this heat energy is “lost”. • The energy doesn’t vanish, it just does not appear as useful output work.

  8. 8.2 Efficiency • The efficiency of a machine is the ratio of usable output work divided by total input work. • Efficiency is usually expressed in percent. Output work (J) efficiency = Wo Wi x 100% Input work (J)

  9. Solving Problems • You see a newspaper advertisement for a new, highly efficient machine. The machine claims to produce 2,000 joules of output work for every 2,100 joules of input work. • What is the efficiency of this machine? • Is it as efficient as a bicycle? • Do you believe the advertisement’s claim? Why or why not?

  10. Solving Problems • Looking for: • …efficiency of machine • Given: • …Wi = 2100 J, Wo = 2000 J • Relationships: • % efficiency = Wo x 100 Wi • Solution • 2000 J ÷ 2100 J x 100 = 95% efficient

  11. 8.2 Power • The rate at which work is done is called power. • It makes a difference how fast you do work.

  12. 8.2 Power • Michael and Jim do the same amount of work. • Jim’s power is greater because he gets the work done in less time.

  13. 8.2 Power • Power is calculated in watts. • One watt (W) is equal to 1 joule of work per second. • James Watt, a Scottish engineer, invented the steam engine. • Jame Watt explained power as the number of horses his engine could replace. • One horsepower still equals 746 watts.

  14. 8.2 Power Work (joules) P = W t Power (watts) Time (s)

  15. Solving Problems • Allen lifts his weight (500 newtons) up a staircase that is 5 meters high in 30 seconds. • How much power does he use? • How does his power compare with a 100-watt light bulb?

  16. Solving Problems • Looking for: • …power • Given: • Fweight= 500 N; d = 5 m, t = 30 s • Relationships: • W = F x d; P = W ÷ t • Solution • W = 500 N x 5 m = 2500 Nm • P = 2500 Nm ÷ 30 s = 83 watts • Allen’s power is less than a 100-watt light bulb.

  17. Key Question: What’s your work and power as you climb a flight of stairs? Investigation 8C People Power

  18. Human-powered Transportation • When we move our bodies along, whether by walking, swimming, or skiing, we exert forces over a distance and do work.