What is Calories: Definition and 53 Discussions

The calorie is a unit of energy defined as the amount of heat needed to raise the temperature of a quantity of water by one degree.
For historical reasons, two main definitions of calorie are in wide use. The small calorie or gram calorie (usually denoted cal) is the amount of heat needed to raise the temperature of one gram of water by one degree Celsius (or one kelvin). The large calorie, food calorie, or kilocalorie (Cal, Calorie or kcal), most widely used in nutrition, is the amount of heat needed to cause the same increase in one kilogram of water. Thus, 1 kilocalorie (kcal) = 1000 calories (cal). By convention in food science, the large calorie is commonly called Calorie (with a capital C by some authors to distinguish from the smaller unit). In most countries, labels of industrialized food products are required to indicate the nutritional energy value in (kilo or large) calories per serving or per weight.
Calorie relates directly to the metric system, and therefore to the SI system. It has been regarded as obsolete within the scientific community since the adoption of the SI system, but is still in some use. The SI unit of energy is the joule. One calorie is defined as exactly 4.184 J, and one Calorie (kilocalorie) is 4184 J.

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  1. F

    Energy consumed by weight of gear on a multiday hike

    I'm trying to figure out how many extra kcal I would burn on a 600km hike with a 30,000m (30km) positive gain for every additional 100g (or 1kg, whatever) of gear in my backpack. It would obviously be a quite rough approximation, as there are significant variables such as the efficiency of a...
  2. nomadreid

    Calories not used for digestion while fasting

    A friend, whose knowledge of biology comes primarily from pseudoscientific works, considers occasional fasting beneficial -- on this I will not take a stand, because as far as I know, the jury is still out on this. However, his justifications are annoying, (To paraphrase a notorious quotation...
  3. R

    How to work out Joules needed to perform work

    Hello all! First post here, and I apologize in advance if this question belongs elsewhere- I'll learn as I go. I am interested in knowing more about energy and performing work. In particular, if I have an object I would like to lift, how much energy I need to expend to do that. Take for...
  4. ngrunenberg

    Caloric Restriction and Aging

    Good Evening, I have a question regarding, what seems to be the only proven way to extend life-span, caloric restriction. There seem to be new studies coming out every other month showing that caloric restriction is very positively correlated with an increase in lifespan, as well as a decrease...
  5. Edemardil

    How Many Food Calories with Efficiency %

    I figured out (a) but I am having trouble with (b): (a) What is the efficiency of an out of condition professor who 2.10e5 J of useful work while metabolizing 500 kcal of food energy? (b) How many food calories would a well-conditioned athlete metabolize in doing the same work with an efficiency...
  6. E

    Calculate calories burned from lifting weights?

    Hi all, So I was thinking about how you could calculate the calories burned when lifting weights. The actual energy requirement should be simple enough if I'm not mistaken : Amount of weight in kg * distance traveled per repetition in m * g constant * number of reps = Joule expenditure Then...
  7. V

    Does a person burn calories when lowering a weight?

    Homework Statement A person exercises daily by lifting weights. When he lifts a weight, he is exerting a force on it to displace it. This means he is doing work and therefore burning calories. But when he lowers the same weight, does he do any work and burn calories? Homework Equations W = F x...
  8. R

    I How to calculate the calories burnt during walking

    Based on Laws of Physics, how to calculate the calories burnt by a person, weighing 60 kg during walking at a speed of 4 kmh–1 for 1 hour. Surprisingly different answers were given by online calculators. Though I am not a Physicist, please let me know the formula or principle behind the...
  9. S

    Coffee + Sugar = Extra Calories?

    I am a big physics enthusiast, and I apply my learning as much as possible. Today, my literature teacher introduced this idea that when coffee and sugar are combined, new calories are born. For instance, coffee (0 kcal) + sugar (100 kcal) = 150 kcal? Unfortunately, I only pursued physics and...
  10. Stephanus

    Energy Released by Hydrocarbon Reactions

    Dear PF Forum, First of all, I'd like to thanks PF Forum for giving me invaluable answers all this time. Now, I have a "situation" here. My church wants to conserve environment by changing cooking oil into biodiesel from its parishioners I'd like to know how effective this effort is. I have...
  11. Eclair_de_XII

    How do I convert BTUs to calories?

    Homework Statement "The use of the British thermal unit (Btu) is common in much engineering work. A Btu is the amount of heat required to raise the temperature of 1 lb of water by 1°F. Calculate the number of joules in a Btu. Homework Equations "A calorie was originally defined as the amount...
  12. K

    Calories generated in brakes of a machine

    Homework Statement A 1000 kg mass car is driving at 3 [m/sec], how many kcal develop in the brakes till full stop Homework Equations Kinetic energy: E=\frac{1}{2}mv^2 Energetic equivalent of a kcal: 4186 [joule] The Attempt at a Solution ##E=\frac{1}{2}1000\cdot 9=4500[joule]##...
  13. K

    Solving Calories Problem: Lose 6kg in 42 Days

    Homework Statement By taking 'daily input' of 2200 kcal your body weight doesn't change. If you decide to lower your 'daily input' for 700 kcal, you will lose 100 grams a day. You want to lose 6 kg in the next 42 days. How big is your 'daily input' going to be? The Attempt at a Solution...
  14. Drakkith

    Calories Required to Raise the Temp of Aluminum

    Homework Statement How many calories are required to raise the temperature of 26 grams of aluminum from 20°C to 115°C? Homework Equations Specific heat of aluminum is 0.22 cal / g x °C Amount of heat = SH x mass x (T2-T1) The Attempt at a Solution Plugging numbers into the 2nd equation...
  15. O

    Convert Joules to Calories - 1 cal = 4.184 J

    Homework Statement 1 calorie is the energy needed to raise the temperature of 1 gram of water by 1 degree Celcius, i.e., the specific heat of water is 1 calorie/g-°C. How many joules is 1 calorie? Homework Equations ΔU = nαkΔT The Attempt at a Solution I attempted to use...
  16. fluidistic

    Using calories of food (as a human body), several questions

    Hello, I would like to understand what exactly is meant by "calories" when we read for example that a chocolate bar has 300 kcal. I understand what is a (kilo)calorie. What I do not know is whether the written values are the raw values in calories or if they are the values our body can...
  17. A

    Physics heat problem Using calories.

    Homework Statement How many calories will it take to raise the temperature of a 44 g gold chain from 20°C to 125°C? Homework Equations You are trying to raise the temperature of 44 g. of gold by 105 degrees celsius. I tried 44 x 105 but this answer was incorrect. [b]3. The...
  18. MathematicalPhysicist

    Running Vs Walking wrt calories burn. (mathematical question).

    Suppose we have a person, A, who we know his/her physique and biological properties, assume he runs a distance, x, versus the same person walking a distance Bx, where B is some parameter we're doing our optimization on which is >1. Can you find me the minimum value of B for which the same...
  19. PhizKid

    Converting joules to calories

    Homework Statement Convert 4.18 joules/(grams * Kelvin) to calories/(pound * Farenheit) (heat) Homework Equations 1 Kelvin = -272 Celcius 1 Calorie = 4.18 Joules 1 Celcius = 33.8 Fahrenheit 1 lb. = 454 grams The Attempt at a Solution \frac{4.18 Joules}{1 gram \cdot 1 Kelvin}...
  20. S

    Need help with a problem involving work and calories

    Homework Statement A person whose mass is 70 kg runs up a flight of stairs through a vertical height of 6 m. If she uses her food with an efficiency of 10%, how many food calories does she have to consume to do this work? Homework Equations P.E=mgh=W (Output/input)*100 = Efficiency The...
  21. F

    Burning Calories by radiation (Stefan-Boltzman law)

    Homework Statement An ice cream cone has 290 Calories. Assuming the temperature of your skin is 32.7 C and the temperature of the air is 19.9 C, how long (hours) will it take to radiate away the energy of the ice cream cone. The emissivity of the average body is 0.915 and the average surface...
  22. K

    Trying to figure out how many calories I burned

    Hey guys, this isn't a homework question or anything. I ended up lugging a lot of wood the other day and decided I would try to figure out on my own how to find out how many calories I burned. I have a ton of data, but I'm just going to show you what I have done via this picture; hopefully...
  23. bohm2

    Medical Are all calories equivalent for fat loss?

    Which position offers stronger evidence? Please vote: No or Yes. Here are a few papers taking each position: 1. No, all calories are not created equally: Evidence: a. Under Free-living conditions: Effects of Dietary Composition on Energy Expenditure During Weight-Loss Maintenance...
  24. C

    How many calories does a plant photosynthesize per day?

    Hello, Related to a thought of why animals don't use photosynthesis (typical answer is that photosynthesis would provide only marginal energy compared to the needs of an animal), I am interested in how much energy does a plant produce using photosynthesis? Any example or estimates is good...
  25. S

    Medical How do calories cause weight gain?

    It may superficially sound like a stupid question with a simple answer, but let me explain in more depth. Calories are units of energy, as you probably know, and grams are the the weight of the food. So calories are not directly related to the weight of a food. Foods range in the amount of...
  26. L

    Rate will this student burn calories

    rate will this student "burn" calories Homework Statement A student wants to lose some weight. He knows that rigorous aerobic activity uses about 700 kcal/h (2900 kJ/h) and that it takes about 2000 kcal per day (8400 kJ) just to support necessary biological functions, including keeping the...
  27. P

    10 calories for 1 calorie of food

    When people say it takes 10 calories of energy to produce 1 calorie of food are they taking into account the fact that food calories are actually kilo calories? Does it really take 10 kilo calories of energy to make one kilo calorie of food energy? Or do they mean 10 calories of energy to make 1...
  28. W

    Solving for the Amount of Heat in Calories

    Homework Statement A piece of nichrome wire is embedded into a 1-kg block of ice at -10 degrees celcius. A current of 3.0 amperes and a voltage of 12 volts is maintained in the wire. How long will it take to separate the wire from the ice? I only want to solve for the amount of heat in...
  29. H

    Medical Calories per hour & cardio

    I'm trying to figure out the realistic calorie burn for a person involved in a cardiovascular activity. Google helps little, because there are all sorts of wildly ranging numbers and 99% of them are uncited or second- or third-hand. I'd like a scientific source. Let's assume an untrained...
  30. W

    How to: compute Watts and Calories for for a bicycle, up a hill

    At 6'5", 300 lbs. and old as dirt, I am a walking and rolling testimate to F=ma. This part of my project is difficult for me, because I have never taken a physics class. All the examples I have in books and PF, deal mostly with force moving down a hill. I am trying to compute Watts and Calories...
  31. K

    Final temperature after calories are added

    Homework Statement A 60.5g piece of lead is at 18.6oC. If 328 cal of heat is added to the lead, what is its final temperature? Do not enter units. Homework Equations I was trying to use 328 as the Q value and solve for delta T Q=mCdelta T HOWEVER, this wasn't working. The...
  32. I

    Burning Calories: Calculating Time to Radiate 285 Calorie Donut

    Homework Statement If a person radiates about 67 W of power at room temperature, how long does it take (h) for a person to radiate away the energy acquired by consuming a 285 Calorie donut? Homework Equations i know W=J/s no clue, i need one that involves time. The Attempt at a...
  33. L

    How much heat (calories) is required to raise the temperature

    Homework Statement How much heat (calories) is required to raise the temperature of 20 g water from 15oC to 95oC? The specific heat capacity of water is 1.0 cal/g*oC. Homework Equations The Attempt at a Solution 95-15 = 80oC 80oC *30 g = 2400 cal. Is that basically what you...
  34. Ed Aboud

    Medical Losing Weight: Decrease Calories or Fat Intake?

    Hi all. For a person trying to lose weight should they decrease their calorie intake or their fat intake or both. Sorry if its a stupid question, I know very little about this stuff. Thanks for any help.
  35. B

    Burning Calories, Burning Wood, Grams to Cals?

    Alright so I apologize if this questions seems less "physics" based, but I promise there is a reason I'm posting it here- if you can thoroughly explain this, I'd much appreciate it! FIRST PREMISE: I was recently reading on the forum about the question of burning a log of wood (mass) and...
  36. L

    Calculate Calories Burned from Climbing Stairs

    I climb 300 stairs to my office every morning - can anyone tell me if i weight 280 pounds how many calories i will burn off (approximately) thanks Tired in Liverpool
  37. D

    Where do the calories go when you pop corn?

    I was reading the back of a pop corn bag and noticed that corn has twice as many calories before you pop it. C = kc = 1000xcalories: The bag claims that there is 120C in 3 tablespoons of unpopped corn and 6 tablespoons total. That is 240C for the unpopped corn in the bag. The bag also...
  38. J

    Burning Calories with Stairs: How Many Floors for a Big Mac?

    Homework Statement 1) How many floors do you need to walk up to burn the calories in a big mac? no variable given, that's it! Homework Equations The Attempt at a Solution alright, so by looking things up on the internet, I've found that a big mac is 540 calories. -big mac is...
  39. S

    Converting calories to watts HELP please

    [SOLVED] converting calories to watts HELP please I've tried this problem six times and this is what I keep coming up with. Any help would be greatly appreciated. I realize this is a very simple simple problem but why this is not working for me I do not know. Again Thank You very much for...
  40. P

    Calculating Calories Used Running

    Hello: I am trying to figure out a way to calculate the number of calories burnt running. Before I do on to explain how I am doing this, I realize that there are many calculators out there that will do this for me, my interest is in finding out how this is calculated. I have had some...
  41. N

    Boosting Metabolism: Low Calories & Exercise

    When a person consumes less than 1000-1200 for a long period of time, their body inturn goes to starvation mode right? And your metabolic rate slows down? Then, by exercising your metablism will increase. If you lower your intake but increase the amount of exercise (or even taken to the extreme...
  42. P

    Food, Calories, Weight, Somebody tell me whats going on

    Tonight my father and I got into a debate over the weight of food ingested and its effect on the weight of the body. 4,086 calories is needed to deposit or burn 1 lb of fat 1,000 grams equals 2.2046 lb 1 gram of fat is 9 calories 1 gram of sugar is 4 calories 1,000 grams of fat...
  43. F

    Calorie Tracking with Spreadsheets: Automating Recipe Calories

    Lets say I have the following spreadsheet. A B C D E 1 Ingredient Calories Protein Recipe Calories 2 Banana 100 1 =A2 ? Now what I want to do is let's say I click on cell D2 and type...
  44. R

    Are calories actually burned?

    What really is a calorie? Are calories actually burned? Why is this terminology used? What are the relationship among a calorie to measure food energy, a calorie to measure heat?
  45. M

    Why does popped popcorn have less calories?

    Somebody told me this, giving some stupid explanation of popped popcorn being mostly "air." I didn't believe them because the mass and chemical composition will still be the same, but I just checked a bag of popcorn and it has 10 fewer calories from fat when it's popped than when it's unpopped...
  46. K

    HELP having trouble finding calories

    HELP! having trouble finding calories ok, this is probably the easiest thing in the world, but i guess i wasn't paying attention that day in class...ok, i have the mass, and then length a person climbed up a rope, and it wants me to find the number of food calories used to climb 10m up the...
  47. C

    Need help with physics question about Calories.

    :yuck: Can anyone help me figure out this question? If you have just consumed 500 Calories of food, how many times do you have to walk up a flight of stairs in order to burn all the Calories? A flight of stairs is = to 4 meters 500 Calories * 4180 Joules = 2090000 Joules WORK=JOULES...
  48. M

    Does it make since if it takes 675 food Calories to lift me up 17 ft?

    does it make since if it takes 675 food Calories to lift me up 17 ft look below *IGNORING HORIZONTAL DISTANCE* i got to figure out how much work is done to get myself up from my class to the cafeteria which is 17 ft in vertical hieght PE=mgh my weight is 120 lbs i converted to mass...
  49. R

    100 Calories consumed/mile?

    It is generally thought for every mile you walk or run, you burn 100 calories. Supose one were to walk uptown at a 15 degree climb for 2.5 miles and then walk back down 2.5 miles to the original start. It would seem this is harder than just burning 500 calories on a straight 5 mile walk...