physics 13 thermal energy

If an object radiates more energy than it absorbs, its

- internal energy decreases - temperature decreases

absolute zero

-273 C

weather vs climate

weather is short term and climate is long term

If it takes 3400 cal to raise the temperature of a 500-g statue by 44°C, what is the specific heat of the material used to make the statue?

0.155 cal/g C

A calorie is defined to be the amount of heat required to raise the temperature of

1 gram of water by 1 degree celsius

During 30 minutes of vigorous excercize, a person may give off 180 kcal of thermal energy by evaporation of water from the skin. What volume of water has been lost by the person in this evaporation process?

180 kcal x (1000 cal/1 kcal) = 180000 cal Q = mL 180000 cal = (m)(latent heat of vaporization = 540 cal/g) m = 333.3 g D = M/V (Density of liquid water g/cm^3) = (333.3 g)/ V 1.0 g/cm^3 = (333.3 g)/V V = 333.3 cm^3

During a thermodynamic process, the internal (thermal) energy of a system increases by 20 J after 16 J of work is done on the system. We can conclude that

20 J = Q(in) + 16 J Q(in) = 4 J 4 J has entered the system

How many calories would it take to raise the temperature of a 300-g aluminum pan from 293 K to 373 K?

293 K = 20 degrees C 373 K = 100 degrees C Q = mcT Q = (300 g) (0.215 cal/g C) (80 degrees C) Q = 5160 cals

A typical jogger burns food energy at the rate of about 40 kJ per minute. How long would it take to run off a piece of cake if it contains 400 kcal (=400 Calories)

40 kJ x (1000 J/1 kJ) = 40000 J per minute 400 kcal x (4184 J/ 1 kcal) = 1673600 J 1673600 J / 40000 J = 42 min

What is the change in the internal energy of a system if 15 J of work are done on the system and 6 J of heat are removed from the system?

9 J

How many joules of gravitational potential energy are converted to kinetic energy when 100 g of lead shot falls from a height of 50 cm? How many calories are released to the surroundings if none of this kinetic energy is con- verted to other forms when the shot hits the floor?

GPE = mgh GPE = (0.1 kg) (10 m/s^2) (0.5 m) GPE = 0.5 J joules to cals 0.5 J x ( 1 cal/ 4.184 J) = 0.1195 cals

latent heat

Q = mL

Consider dropping a 12g ice cube into a glass of tea. If the latent heat of melting for ice is 80 cal/g, how much thermal energy is removed from the tea as the ice melts?

Q = mL Q = (12 g) (80 cal/g) = 960 cal

How many calories are required to heat 400 g of water from 23 °C to 33 °C

Q = mcT Q = (400 g) (1 cal/ g C) (10 degrees celsius) Q = 4000 cal

specific heat

The amount of energy required to raise the temperature of 1 gram of a substance by 1 degree celcius

what is temperature

The measure of the average kinetic energy of the molecules.

radiation

The random jiggling motion of the electrons in atoms and molecules cause them to emit electromagnetic waves.

During a thermodynamic process, 12 J of work are performed on a system, while the system gives of 5 J of heat. The internal energy of the system

U=Q(in)+W(on) U stands for internal energy do negative sign if energy released U = -5 J + 12 J U = 7 J positive means increases by 7 J

Why might a cook put large aluminum nails in potatoes before baking them?

aluminum is a good conductor of heat so aluminum in the potato can draw heat in the middle of the potato much faster than without the conductor in the middle

heat capacity

amount of heat it takes to increase the temperature of an object by 1 degree celsius

internal energy

as the temperature of an object increases, its internal energy increases

How do the internal energies of a cup of water and a gal- lon of water at the same temperature compare?

at the same temperature, the larger one will have more internal energy since it has more molecules

Why does tile feel colder than carpet.

both materials are at same temperature, tile is better conductor if heat than the rug, heat is readily taken from food in contact with tile.

greenhouse effect on earths atmosphere

carbon dioxide transmits the incoming solar energy and then reflects the reradiated energy from the earth if we trap too much co2 we will get global warming

In convection, thermal energy is transported by

currents in a heated fluid

The first law of thermodynamics is a statement of...

energy conservation

heat is

energy flowing between 2 objects because of a difference in temperature

energy released when go from

gas to solid

What is the difference between heat and internal energy?

heat is energy that flows from one object to another. internal energy is the total energy of molecules in an object

What is the difference between heat and temperature?

heat is the energy flow from one object to another temperature is a measure of average KE of molecules

2 ways to increase internal energy of system

heat the system or do work on the system

Your feet feel warmer on a rug than on a tile floor because the tile

is a better thermal conductor

1 calorie

is defined as the amount of heat that raises the temperature of 1 gram of water by 1°C 4.184 J

Does it take more thermal energy to raise the tem- perature of 5 grams of water or 5 grams of ice by 6°C? Explain.

it takes more thermal energy to raise the temperature of water since the specific heat of water is larger than the specific heat of ice (Aka its easier to melt ice)

A kettle containing 3 kg of water has just reached its boil- ing point. How much energy, in joules, is required to boil the kettle dry?

latent heat = mL Q = mL Q = (3 kg) (2260 kJ/kg) Q = 6780 kJ = 6780000 J

How much heat is required to raise the temperature of 500 g of water from 20°C to 30°C?

q = mc t q = (500 g)(1 cal/ g C)(10 degrees C) q = 5000 cal

How many calories are required to raise the temperature of 8 grams of water by 5°C?

q = mcT q = (8 g)(1 calorie/ gram C)(5 C) q = 40 calories

greenhouse effect

short wavelength radiation from the sun is transmitted through the glass. long wavelength reradiated energy is not transmitted out through the glass and is trapped inside

In an avalanche, the snow and ice begin at rest at the top of the mountain and end up at rest at the bottom. What happens to the gravitational potential energy that is lost in this process?

snow and ice have GPE at top of mountain, then as they go down they become KE and eventually at rest again and becoming thermal energy. there a small increase in temperature.

energy absorbed when go from

solid to gas

thermal energy

the internal energy of an object due to the kinetic energy of its atoms and/or molecules

The electromagnetic energy radiated by the sun is concentrated in the visible, whereas the electromagnetic energy radiated by the Earth is predominantly in the infrared. This is because

the sun is much hotter than the earth

heat is

thermal energy that is transferred from one object to another due to their temperature difference

when objects increase in temperature, they tend to experience

thermal expansion

conduction

transfer of thermal energy by collisions of molecules within a substance or at an interface

convection

transfer of thermal energy in fluids by the physical movement of the fluid example is radiator that moves (warmer fluid/air) to the cooler fluid/air.