For 50 percent of America’s population, one of the first things they do in the morning is have a cup of coffee. Most of these people stir their coffee and then add the usual milk or cream into their coffee. Have you ever wondered why when you pour the milk into the cup of coffee a dimple is formed in the middle of the cup? Does the temperature of the milk have anything to do with this phenomenon?
When you add the milk to the coffee after you have stirred it a dimple is formed towards the middle of the cup, this is called a vortex. The vortex is caused because the denseness of the milk is greater than the coffee which makes it sink. Vortices cause dimples on their own so what makes it different in this case is that the swirling that you make with the spoon plus the density of the milk cause the dimple you see. The swirling motion of the milk is explained by Newton’s 1st Law of Motion. This law states that something in motion will stay in motion unless an external force is applied to it. Since you started stirring the coffee before pouring the milk, putting the milk isn’t going to stop the swirling. In the video entitled, Coffee Cup Vortex on YouTube you can see exactlywhat is suppose to happen when you do this.Coffee Cup Vortex
Say one morning you are making your coffee and instead of placing cold milk or cream in your coffee you decide to place warm milk in it. You start by taking your spoon and you stir the coffee and then pour in the warm milk just as you did with the cold milk. You then notice something unusual. When adding warm milk to the coffee the dimple or the vortex isn’t formed. This is surprising because you would usually think that the temperature of the milk would not make a difference and the same thing would happen. When you heat up the milk you actually decrease its density. Since the milk is now less dense it no longer is being pulled down to the bottom of the cup as it was when it was cold. This all happens because when the temperature of something is greater the energy is increasing which then makes the molecules expands. This would explain why the milk decreases in density as it warms up.
The next time you go to pour yourself a cup of coffee try out these fun simple experiments. You would have never guessed that each morning when you were making your coffee you were working with physics.
Gonick,L., Hoffman, A.(1991).The Cartoon Guide to Physics. United States : Harper Collins
This book is used for Physics classes but takes a different approach to how it talks about Physics. The information that I used for this paper talked about heating of air or liquids and how the molecules expand when the temperature is increased. I used this to explain how the milk when it is heated because less dense. This information is for the most part very reliable. This is a book that is used in college Elementary Physics classes and all the information coincides with the information in other texts and information on the internet. This helped me just a little bit in my research because it helped me explain the milk idea. It didn’t specifically talk about milk but I took the basics idea from this book and used it for the question. I think that this was an ok source because it gave me some information I just had to interpret it and see how it pertained to my question.
Neal, R. (2002). Caffeine Nation. Retrieved October, 15, 2009 from
This article talked about how many Americans drink coffee each and everyday. It tells us how much people drink coffee and why people drink coffee. Its overall goal is to show American how addicted we are to caffeine. This was relevant to my question just in the sense that I wanted to engage my readers by stating how many of them probably drink coffee each day. I thought this wasn’t the best website I just wanted to find a statistic and I did. I didn’t really use it to help state my question I just used it for my opening paragraph. I think that this information was pretty reliable because it gave me different sides and opinions and it didn’t seem bias.
(2006).Newton’s Laws of Motion. Retrieved October 16, 2009 from
This website just talked about all of Newton’s Laws of Motion. For my question I needed to talk about his 1st law and this site gave me a good explanation of it. I think that the information in this site was reliable. It was made by a University which to me gives it credibility. I think that it is also reliable because it coincides with the other resources that talk about Newton’s laws. This website was pretty useful for my research because it helped me put this law into my paper and relate it to my question. I think that for what I wanted from him it did a good job.
(2009). Coffee Cup Vortex. Retrieved October 24, 2009 from
This is a YouTube video that shows what a vortex in a coffee cup looks like. I think that this will help my audience exactly what they should be looking for when they do this experiment. I don’t think that this is the most reliable source or video but I think that it does a good enough job of explaining and showing what I want it to show.