仕事、エネルギー、出力
国際バカロレア · IB Diploma · Physics · HL トピック 3 3:49 英語ナレーション・英語＋中文字幕 burning-in
章
Transcript
A motor can transfer some input energy to lifting and the rest to heating.
电动机可以将部分输入能量用于提升，其余部分转化为热能。
Useful output is part of the total energy transfer.
有用输出是总能量传递的一部分。
Work done by a constant force parallel to displacement is force multiplied by distance.
恒力沿位移方向所做的功等于力乘以距离。
Kinetic energy depends on speed squared.
动能与速度的平方有关。
Energy is conserved when all transfers and stores are included.
把所有的能量转移和储存都计入时，能量守恒。
Power is energy transferred per unit time.
功率是单位时间内转移的能量。
Efficiency is useful output divided by total input.
效率是有用输出除以总输入。
Define the system and useful output before calculating efficiency.
在计算效率之前，先定义系统和有用输出。
Doubling speed quadruples kinetic energy at constant mass.
质量不变时，速度加倍会使动能变为原来的四倍。
Power describes transfer per time, not total energy.
功率描述的是单位时间内的能量转移量，而非总能量。
In the lab: Measure a lifting height and load, time the lift, and record electrical input with suitable instruments.
在实验室中，测量提升高度和负载，记录提升时间，并使用合适的仪器记录电输入。
Repeat trials and account for heating or friction as transfers, not missing energy.
重复试验，并将加热或摩擦视为能量转移，而非能量损失。
Known: a device receives 600 J and transfers 420 J usefully.
已知：某装置接收 600 J 能量，其中有用输出为 420 J。
Efficiency equals useful output divided by total input.
效率等于有用输出除以总输入。
Efficiency equals 420 divided by 600, which is 0.70, or 70 percent.
效率等于 420 除以 600，即 0.70，或 70%。
Over 3 s, useful power equals useful energy divided by time, which is 420 divided by 3, equaling 140 W.
在 3 s 内，有用功率等于有用能量除以时间，即 420 除以 3，结果为 140 W。
Your turn: A device receives 250 J and gives 150 J useful output.
请作答：某装置接收250 J能量，并输出150 J有用功。
Find efficiency as a percentage.
求其效率百分比。
Pause the video and work it out.
请暂停视频，自己算一算。
Check: 150 joules divided by 250 joules is an efficiency of 60 percent.
核对：150 焦 ÷ 250 焦，效率为 60%。
Efficiency cannot exceed 100 percent for a properly defined energy balance.
对于正确定义的能量平衡，效率不能超过100%。
Energy dissipated by heating is still conserved.
通过加热耗散的能量仍然守恒。
Not true: Dissipated energy is destroyed.
不正确。 耗散的能量并未被销毁。
Energy is always conserved.
能量始终守恒。
"Dissipated" means spread into the surroundings as heating, where it becomes hard to use again - not destroyed.
“耗散”是指能量以热的形式分散到周围环境中，使其难以再次利用，而非被销毁。
Work done by a constant force parallel to displacement is force multiplied by distance.
恒力沿位移方向所做的功等于力乘以距离。
Define the system and useful output before calculating efficiency.
在计算效率之前，先定义系统和有用输出。
Watch for: efficiency cannot exceed 100% for a properly defined energy balance.
注意：对于正确定义的能流平衡，效率不能超过100%。
A device receives 200 J and gives 90 J of useful output.
一个装置接收了200 J的能量，并输出90 J的有用功。
Find the efficiency.
请计算其效率。
The other energy is dissipated, not destroyed.
其余能量被耗散，而非消失。
The result is an efficiency of 45 percent.
结果是效率为45%。
Of the 600 joules supplied, 420 are useful output and 180 are dissipated.
在提供的600焦耳中，420焦耳是有用输出，180焦耳被耗散。
Energy is conserved: 420 plus 180 is 600.
能量守恒：420加180等于600。
The efficiency is 70 percent.
效率为百分之七十。
A fictional device receives 500 J in 4 s and delivers 300 J usefully.
一个虚构装置在4秒内接收500焦耳的能量，并有用地输出300焦耳。
Find input power, useful power and efficiency; account for the remainder.
求输入功率、有用功率和效率；并说明剩余能量的去向。
Input power 125 W, useful power 75 W, efficiency 60%.
输入功率为125 W，有用功率为75 W，效率为60%。
The remaining 200 J goes to other transfers or stores.
剩余的200 J用于其他转移或储存。
Define the task and system before calling energy useful.
在称能量为有用之前，先定义任务和系统。
Pause and check yourself. Explain each point on screen in your own words, then change one number in the last example and say which assumption must still hold.
暂停一下，自我检查：用自己的话解释屏幕上的每个要点，再改动最后一个例子中的一个数字，说明哪个假设仍然必须成立。