LECTURE 27 ENERGY IN THE BODY

Transcription

1 LECTURE 27 ENERGY IN THE BODY 11.1 Transforming energy Efficiency 11.2 Energy in the body Getting energy from food: energy input Using energy in the body: energy output Efficiency of the human body Energy storage Energy and locomotion The LED light bulbs are far more efficient (and cost effective) than incandescent light bulbs.

2 Learning objectives 2! Use the concept of efficiency and calculate energy used by the body to perform different tasks.

3 Quiz: ! When you walk at a constant speed on level ground, what energy transformation is taking place in you? A. E chem U g B. U g E th C. E chem K D. E chem E th E. K E th

4 Quiz: answer 4! When you walk at a constant speed on level ground, what energy transformation is taking place in you? A. E chem U g B. U g E th C. E chem K D. E chem E th E. K E th! The chemical energy stored in food is converted into thermal energy of the person as the person gets hotter.! The person is walking at a constant speed, so kinetic energy remains constant.! The person is walking on a level ground, so the gravitational potential energy of the person- Earth system remains constant.

5 11.1 Transforming energy 5! Energy cannot be created or destroyed, but it can be transformed. " = $ + &' + &( + ")* + "+*,- + = / + 0!!! Work is positive when energy is transferred into the system and negative when energy is transferred out of the system. We will broaden our definition of work to include energy transfer into or out of system of radiant and electric energies. When other forms of energy are transformed into thermal energy the change is irreversible. The energy isn t lost, but it is lost to our use.

6 11.1 Efficiency 6! The general definition of efficiency is! = what you get what you had to pay! Process limitations, due to practical details, and fundamental limitations, due to physical laws, can reduce efficiency.

7 11.2 Getting energy from food: energy inputs 7! The chemical energy in food provides the necessary energy input for your body to function.! Food is broken down into simpler molecules such as glucose and glycogen that are metabolized in the cells by combining with oxygen.! This metabolism releases energy, much of which is stored in adenosine triphosphates (ATP s). Cells in the body use this ATP for muscle contraction and nerve signal propagation.

8 Quiz: ! An energy bar contains 23 g of carbohydrates. How much energy in J from carbohydrates does it contain?

9 Quiz: answer 9! An energy bar contains 23 g of carbohydrates. How much energy in J from carbohydrates does it contain?!! = 23 g of carb,-,/0 1, = = J

10 Quiz: ! How many Calories of energy does 1 g of carbohydrates provide?! 1 food calorie = 1 Cal = 1 kcal = 4190 J

11 Quiz: answer 11! How many Calories of energy does 1 g of carbohydrates provide?!!" #$ =!"!./ $! % &' ()*+! % &' ()*+! 0)1 2!3. $ = 2 0)1! % &' ()*+! You may have learned in a health or nutrition class that 1 g of carbohydrates provides about 4 Cal of energy.! FYI: 1g of fat provides 9 Cal of energy.

12 Quiz: ! An energy bar contains 23 g of carbohydrates. How much energy is this in Calories?

13 Quiz: answer 13! An energy bar contains 23 g of carbohydrates. How much energy is this in Calories?! 23 g of carb * +,-. / 01 2,34 = 92 Calories

14 11.2 Using energy in the body: energy outputs 14! At rest, your body uses energy to build and repair tissue, digest food and keep warm.! The energy is converted almost entirely into thermal energy, which is transferred as heat to the environment.

15 Quiz: ! How much energy in Calories do you need for you to rest all day assuming your mass is 68 kg? This amount of energy is called BMR (Basal Metabolic Rate).

16 Quiz: answer 16! How much energy in Calories do you need for you to rest all day assuming your mass is 68 kg?!! = # % = 100 ( ) 2000 Calories 24 hours 1233 ) :; <4=3 (! If you look at a food label, you will see ingredient contents compared to a 2,000-calorie average diet. =

17 11.2 Using energy in the body: energy outputs 17! When you engage in an activity, your cells require oxygen to metabolize carbohydrates.! You can measure your body s energy use by measuring how much oxygen it is using.! Total metabolic energy use is all of the energy used by the body while performing an activity.

18 11.2 Efficiency of the human body 18! We typically consider the body s efficiency to be 25%.

19 Quiz: ! Suppose your mass is 68 kg, and you climb a 2.7-m-high flight of stairs. How many Calories do you burn? Assume your body s efficiency is 25 %.

20 Quiz: answer 20! Suppose your mass is 68 kg, and you climb a 2.7-m-high flight of stairs. How many Calories do you burn? Assume your body s efficiency is 25 %.! Consider the system of you and the earth. As you climb, the gravitational potential energy of the system increases.!! = #$%& '() *+& #$%& '() $%, &( -%' = / = ! 9 :);< = 678 = = A.? D EF I.GJ G.H D = P J R S%T URAI V = 1.7 Cal

21 Quiz: ! Suppose your mass is 68 kg, and as you climb a 2.7-m-high flight of stairs, you burn 1.7 Calories. If you eat an energy bar that gives you 92 Calories of energy, and if it s the only source of energy, how many flights of stairs can you climb?

22 Quiz: answer 22! Suppose your mass is 68 kg, and as you climb a 2.7-m-high flight of stairs, you burn 1.7 Calories. If you eat an energy bar that gives you 92 Calories of energy, and if it s the only source of energy, how many flights of stairs can you climb?!! = # $%$&'$(') # (*+,-.)+ /'&01- = = 54 /lights of stairs

23 Quiz: ! Suppose your mass is 68 kg, and you eat an energy bar that gives you ' J (92 Calories) of energy. If it s the only source of energy, and if you walk at 5.0 km/h, how far in km could you walk?

24 Quiz: answer 24! Suppose your mass is 68 kg, and you eat an energy bar that gives you ' J (92 Calories) of energy. If it s the only source of energy, and if you walk at 5.0 km/h, how far in km could you walk?! As you walk at 5.0 km/h, your metabolic power is 380 W.! So you last the duration of * =, -.-/ ! If you walk at 5.0 km/h for the duration of *, you walk a distance of 4 = 5 * = 5, 3 = : 9 ;<== > ;.? A ;B= C = 1.4 km

25 11.2 Energy storage 25! Energy from food that is not used will be stored.! If energy input from food continuously exceeds the energy outputs of the body, the energy is stored as fat under the skin and around the organs.

26 11.2 Energy and locomotion 26! When you walk at a constant speed on level ground, your kinetic and potential energy are constant.! You need energy to walk because the kinetic energy of your leg and foot is transformed into thermal energy in your muscles and shoes, which is lost.