Right now we're going to talk about demand, and since demand has to do with buyers and consumers, I'm going to explain it all consuming this gallon of milk.

現在我們要來談談需求，因為需求涉及到買家與消費者，所以我會邊解釋邊喝這一大瓶的牛奶。

So here we go, let's start it out.

所以我們開始吧！

That first taste of milk is just wonderful, right? Cold, refreshing.

第一口的牛奶超棒，又冷又提神。

The first thing you have to understand about demand is the law of demand, which says that there's an inverse relationship between price and quantity demanded.

第一件該知道的是《需求定律》，也就是價格和需求量成反比。

That means when the price goes down, the quantity demanded increases.

意味著價格下降時，需求量會增加。

And if the price goes down, the quantity demanded goes up again.

若價格再下降，需求量會再增加。

So take a look at this demand schedule.

看看這張需求表。

As you can see, when the price goes down, the quantity demanded goes up.

可以看出當價格下降時，需求量會上升。

When the price goes down to four, three, two, and one, the quantity demanded increases.

價格越低時，需求量越多。

Now when you plot these points, you're gonna get a demand curve, which looks like this.

當你把這些點繪製成圖時，你會發現一條需求曲線，如圖所示。

It's a downward sloping curve showing the law of demand.

這是一條向下延伸的斜曲線，這就是需求定律。

Now there are three reasons why the demand curve is downwards sloping.

這條需求曲線之所以向下傾斜，有三個原因可解釋。

It's the reason for the law of demand, it's the substitution effect, the income effect, and the law of diminishing marginal utility.

也就是需求定律的原理：《替代效應》、《收入效應》，以及《邊際效用遞減法則》。

Substitution effect says price goes down for milk, people are going to buy more milk, because they're going to move away from other products that are now more relatively expensive.

替代效應即當牛奶價格下降時，大家會買更多牛奶，因為其他物品相對較貴。

So instead of buying juice, people are going to turn around and go buy more milk.

所以與其買果汁，大家會轉而跑去買更多牛奶。

Now that goes the other way, when the price goes up for milk, the quantity demand for milk's going to decrease.

反之亦然，當牛奶價格上漲，其需求量就會減少。

Because people are going to move away from the milk and go find a different substitute product.

因為大家會找替代品取代牛奶。

I wish I could find a substitute product.

我希望可以找到替代的產品。

Now the income effect says that when the price goes down, people buy more milk, because their purchasing power has increased.

收入效應指出當價格下降時，大家會買更多牛奶，因為他們的購買力上升了。

So if you go to the store, and you find out that milk is on sale and it only costs one dollar for a gallon of milk, you're going to buy more because you can buy more.

所以當你去店裡發現牛奶在促銷，一加侖只要一美元時，你會買更多，因為你可以買更多。

The amount you can buy with each dollar has increased, and of course it goes the other way.

現在每一美元能買的東西變多了，當然反之亦然。

If the price goes up for milk, people are gonna stop buying milk, because their purchasing power has decreased.

如果牛奶價格上升，大家就不買牛奶了，因為他們的購買力下降。

Each dollar gets them less milk.

每一美元能買到的牛奶變少了。

And the third reason for the law of demand is something called the law of diminishing marginal utility.

需求定律的第三個原因就是邊際效用遞減法則。

Remember utility is satisfaction and marginal is additional.

要記得：效用即滿足感，而邊際就是額外增量。

So this is the law of decreasing additional satisfaction.

所以這就是減少額外滿足感的定律。

The law says, as you consume anything, like milk, the additional satisfaction you're going to get, is going to start to eventually decrease, which is exactly what's going on right here.

定律指出，當你消耗如牛奶等產品時，額外的滿足感最終會減少，就像現在發生的事。

That very first sip was super refreshing, but that last one not so much.

第一口很清涼，但最後一口並非如此。

Now this law applies to somebody drinking sips of milk, but it also applies to purchasing gallons of milk.

這個定律不僅適用於喝牛奶，買牛奶同樣的道理。

That very first gallon of milk you get for your family, is awesome, it gives you a lot of satisfaction.

買給家人的第一瓶牛奶很棒，因為你得到很大的滿足感。

You can have your milk and cookies, you can eat your cereal.

可以喝牛奶配餅乾、麥片。

Your second gallon of milk gives you some utility.

第二瓶會帶給你一些效用。

And the third gives you some utility, but the law says eventually, each additional gallon of milk that you consume is going to give you less and less additional utility.

第三瓶也會帶給你一些效用，但定律指出，最終每多喝一瓶牛奶，帶給你的效用就越少。

This concept explains the law of demand, and the shape of the demand curve because they get people to buy more quantity of milk.

這個概念解釋了需求定律與需求曲線的樣子，因為這促使人們買更多牛奶。

The price has to go lower, because they get less and less additional satisfaction from each gallon of milk.

價格必須越來越低，因為消費者從牛奶上得到的滿足感會越來越少。

It's getting warm. It's getting warm.

快退冰了，快退冰了。

So a change in price goes along the demand curve, but if something else other than price changes, it'll actually shift the demand curve.

所以價格的改變依附在需求曲線上，但如果有價格以外的因素改變，需求確實也會跟著改變。

For example, let's say a study comes out that says milk causes baldness, that would cause the entire demand curve to shift left.

例如，如果有研究指出牛奶會導致禿頭，那就會影響整個條曲線向左移。

At every single price, people are going to buy less, and so the curve shifts to the left.

不管價格如何，需求都會減少，所以曲線向左移。

That's called a decrease in demand, the opposite is an increase in demand, and so at every single price people want to buy more.

意即需求下跌。相反地，當需求增加，那不管價格如何，大家的購買量都會變多。

So the demand curve shifts to the right.

因此曲線向右移。

Now there's five shifters, or determinants of demand.

有五個影響曲線的因素，或說是需求的決定因素。

These are the things that cause the demand curve to shift.

以下是影響曲線移動的的因素。

The first shifter of demand is taste and preferences.

第一，品味與偏好。

For example, what if a new study comes out that says kids who have milk in the morning before they go to school, do better at school and they're smarter?

例如，如果有新的研究報導說早上上學前喝牛奶，小孩在校的表現會比較好，且頭腦較聰明？

Well, that would increase the demand, the demand curve would shift to the right.

這樣會增加需求，導致需求曲線向右移。

Another shifter would be the number of consumers.

第二，消費者的數量。

What if all of a sudden, new customers come into town.

突然一群新的消費者湧入市區。

That's going to increase the demand for milk.

就會增加牛奶的需求。

Another shifter is the price of related goods, substitutes and complements.

另一個影響因素就是相關產品、替代品和補充品的價格。

For example, almond milk and cows milk are substitutes for each other.

例如，杏仁奶和牛奶可以彼此替換。

That's a bad idea.

不該這麼做。

So if the price goes up for almond milk, and it's more expensive to buy this, then the demand's gonna increase for cow's milk.

所以若是杏仁奶價格上漲，需求則會轉向牛奶。

If the price goes down for almond milk, that means people are going to move away from buying cow's milk, buy more almond milk.

如果杏仁奶價格下跌，意味著大家將減少購買牛奶而買更多杏仁奶。

So the demand for cow's milk will fall, and of course there's also complements.

所以牛奶的需求會下降，當然補充物也會受影響。

So when the price of cereal falls, that's going to increase the demand for milk.

所以當麥片價格下跌，牛奶的需求會跟著增加。

Now the next shifter is income.

下一個因素是收入。

Income is a little tricky because it depends on the type of product, there's normal goods and inferior goods.

收入這項有點微妙，因為這取決於產品的類型，有分「正常財」與「劣等財」。

So let's say that milk was a normal good.

我們把牛奶歸類為正常財。

This means when there's an increase in income the demand's going to increase.

這就表示當收入增加時，需求就會增加。

When there's a decrease in income, the demand's going to decrease.

如果收入減少，需求就跟著減少。

An inferior good is just the opposite, when there's an increase in incomes the demand falls, and when there's a decrease in incomes the demand will go up.

劣等財正好相反，收入增加時需求就減少，收入減少時需求就增加。

So whenever you see a question that involves income, make sure to read the question carefully to find out if it's a normal good or an inferior good.

所以你看到有關收入的問題時，要確認是和正常財還是劣等財有關。

The last shifter of demand is a change in expectations.

最後一個因素是預期心理的改變。

So for example, if you think the price of milk is going to decrease next week, you're going to buy less today and so the demand will decrease.

如果你認為下週牛奶價格會下跌，今天就會少買一點，造成需求減少。

But if you think the price is going to increase next week, you're actually going to buy a whole lot more today.

如果你認為下週價格會上漲，你今天就會買更多。

So that's going to increase the demand.

因此需求上升。

Now it's time to cover a super important detail that you have to watch out for.

現在該談到一個你必須小心留意的重要小細節。

It's the difference between a change in quantity demanded, and change in demand.

需求量改變與需求改變是不同的。

So look at this graph for milk, right now you see three points: A, B, and C.

看看這張牛奶的曲線圖，上面有 A、B 和 C 三點。

And there's two ways to go from ten to twenty units. Movement from A to B along the demand curve is a change in quantity demand.

從十移到二十單位有兩種方法。沿著曲線從 A 趨向 B 點是因為需求量改變。

So when the price goes down from three dollars to two dollars, the quantity demanded goes up from ten to twenty.

所以價格從三美元降至兩美元時，需求量從十上升到二十。

Now A to C is a change in demand, price doesn't change, price stayed at three but people decided to buy more, why?

A 點到 C 點是由於需求的改變，價格維持在三美元，但大家決定買更多，為何？

Well, because the five shifters, like taste and preferences that people prefer and want more milk then the entire demand curve will shift to the right.

因為上述五個因素，像是品味與偏好。大家就是想買更多牛奶，所以需求曲線會向右移。

At that same three dollar price, people want more so that's a change in demand.

同樣是三美元，但大家想買更多，所以需求改變。

It's a change in demand.

這就是需求改變呀。

So I got a question for you, what happens to the demand when the price goes down?

所以我問個問題，當價格下降時，需求會如何變化？

Oh, gosh this is a bad idea!

不，真的不該這麼做。

So the answer is nothing.

答案是維持不變。

When the price goes down, demand stays exactly the same.

價格下降，但需求不變。

Prices causes the quantity demanded to change. The only thing that changes quantity demanded is a change in price.

價格影響需求量，唯一改變需求量的是價格波動。

And the only thing that changes demand is one of the five shifters of demand.

唯一改變需求的是五個因素其中之一。

Oh man, I think I'm lactose intolerant, I need those Cheerios.

我想我乳糖不耐啦，我要吃些麥片。

We're good. We're good. And we're done.

沒事、沒事。喝完啦！

Make sure to take a look at the next video which explains supply, the law of supply and the shifters of the supply curve.

記得要看看下一部影片，其解釋了供給、供給定律，以及影響供給曲線的因素。

Now don't forget to subscribe or leave a comment bellow, alright? Until next time.

別忘了訂閱或留言好嗎？下次見囉！