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Measuring Energy

Measuring Energy. YEAR 8 PHYSICAL SCIENCE. Student Objectives. By the end of this lesson you will be able to recall the units of measurement for energy, work, and power. 1 MINUTE REVIEW. Last lesson we looked at the definitions of energy, work and power. Do you remember their definitions?

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Measuring Energy

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  1. Measuring Energy YEAR 8 PHYSICAL SCIENCE

  2. Student Objectives • By the end of this lesson you will be able to recall the units of measurement for energy, work, and power.

  3. 1 MINUTE REVIEW • Last lesson we looked at the definitions of energy, work and power. • Do you remember their definitions? • Be prepared to share your ideas

  4. Definitions Energy is the ability to do work and isused in order to perform work. Work is a force over a distance acting to move or change an object Power is how fast work is done (or the rate at which work is done)

  5. Measuring Energy - JOULES • Both energy and work can be measured in a unit called the joule (j). • Joule is another name for newton·metre. If you push an object along the floor with a force of 1 newton for 1 metre, you have done 1 joule of work.

  6. Comparing units of energy • 1 kilojoule = 0.2388 calories or 0.948Btu • 1 calorie = 4.19kJ or 0.0039Btu • 1 British thermal unit (Btu) = 1.055kJ or 252 calories.

  7. Calculating Energy YEAR 8 PHYSICAL SCIENCE

  8. Student Objectives • By the end of this lesson you will be able to use formulae to calculate work and power.

  9. 1 MINUTE REVIEW • What are the units used to measure work and energy? • What is the unit used to measure power? • What is the unit used to measure force? BE PREPARED TO SHARE YOU ANSWERS

  10. MEASURING WORK • To calculate the amount of work being done we use this equation: W = F×d Where W = work (joules) F = force (newtons) d = distance (metres)

  11. Example • Work = magnitude of Force (N) × distance (m) • If I pushed a chair 5 metres with 20N of force how much work would I have done? • Work= _____N (force) x ___metres (distance) • Work = _______ J or _________ kJ

  12. Measuring Power • To calculate the amount of power being used we use this equation: P = W/ t Where P = power (watts) W = work (joules) t = time (seconds)

  13. Example • Power = work (J) / time (seconds) • If I pushed the chair for 3 seconds and it took 1500 joules (1.5kJ) of work to move the chair how much power did I use? • Power = ______J (work) /___ seconds (time) • Power = _____ watts

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