Food

Is Your Coffee Cold? Try Yelling at It


#physics #science #coffee #temperature #yelling How to heat your coffee by yelling

If taking a sip of cold coffee gets your dander up, making you want to yell, you might as well go ahead and let loose. You can actually heat your coffee through the power of your voice.

To heat coffee, it takes energy. Sound is a form of energy. Sound waves compress and expand air molecules, causing them to vibrate. The faster they vibrate, the hotter they get. In other words, the louder you yell about your cold coffee, the warmer you will make it.

The average human yells at about 80 decibels. This generates about 0.001 watts of energy. This is about a 100,000 times less than the energy needed to light a standard 100 watt bulb. Of course, we’re not interested in creating light — we just want to warm that cup of java. Try focusing your yell on an average 8 oz. cup of coffee. Each second of yelling will warm the cup of coffee .00000095 degrees Celsius.

For those interested in the math, the formula for calculating the energy needed to change the temperature of any item is:

E = mc(Tf  – Ti)

Plug in the numbers for the variables, where m is the object’s mass, c is the specific heat of the object, Ti is the initial temperature, and Tf is the final temperature. The answer, E, is the number in Joules of the energy needed to achieve the goal.

So how much yelling will you need to do? Let’s assume that the coffee is in a perfectly-insulated cup that allows no escape of heat. Let’s also assume that you are so worked up that your yell is constant. Your coffee starts out at an unacceptable 25 C (77 F), and you want to raise it to 75 C (167 F). For sake of convenience, let’s round the 8 ounces of coffee up to 0.25 kg (8.82 oz). The specific heat for water is 4,182 J/kg °C. Do the math, and you arrive at:

E = .25 · 4,182 (75f – 25i) = 52,275 Joules

Now we know that 52,257 Joules of energy is needed to get the coffee to the desired temperature. All that remains is to know how long you need to yell in order to direct that much energy into your cup. The formula for this is T = E / P, where T is the amount of time it will take to generate E amount of energy and P amount of power. We just determined we need 52,275 Joules of energy, and earlier we said that yelling at 80 decibels produced 0.001 watts of energy:

t = 52,275 / .001 = 52,275,000 seconds

In other words, if you yell at your coffee for 605 days and 50 minutes, you will manage to get your coffee to the desired temperature.

To put it another way, you might as well stop your griping and just go and find a microwave.


Read about how many calories you burn by banging your head against the wall.

Find out how far you have to run to burn off the calories of one M&M.

Read about the quietest room on the planet.

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