Temperature & Heat Warm- up Define Kinetic energy (KE) ____________________________ The KE formula is:_____________ Calculate the kinetic energy of a 3 kg toy car that moves at 4m/s. _____________________________

solution Kinetic energy is the energy of motion Moving motor bike has kinetic energy A running person has KE

solution KE = ½ mv2 ½ (3)(42) 24Joules

Temperature & Heat Define temperature:___________________________________________________

Temperature measurement scale Freezing point Boiling point Fahrenheit 32º F 212º F Celsius 0º C 100º C Kelvin 273 K 373 K

Question The American Meteorological department prefer using Fahrenheit scale to Celsius scale in their weather reports because___________________________________________________________________

Temperature and Kinetic energy What is the relationship between temperature and Kinetic Energy of molecules? Solution: The greater the temperature, the greater the Kinetic energy of the particles (molecules) of the object

Converting Fahrenheit to Celsius Conversion formula F= Temperature in Fahrenheit C = Temperature in Celsius K = Temperature in Kelvin

problem Convert 30 0c to Fahrenheit Solution=

Class work: Convert 45º C into a) Kelvin and b) Fahrenheit. Convert 89 ºF into a) Celsius and b) Kelvin. Textbook Pg 322 # 1-5.

Heat Warm-up 1. What is the formula for work done? ___________________ 2. How many joules of work are done on an object when a force of 10 N pushes it a distance of 10 m? _________________________________

Solution Work done = Force x Distance Work done = 10N x 10m = 100Joules

Heat Heat is defined as energy transferred from one object to another because of the difference of temperature between them. Just as work, heat is a form of energy transfer between systems.

Heat transfer Heat is always transferred from ___________to __________substances. For heat to be transferred from cold to hot, external work has to be done Example External work is done to cool homes ( Air conditioning) Without air conditioning, Heat from outside environment gets into the house to raise the temperature of the house.

Definitions Define the following terms Internal energy:____________ Thermal contact: ___________ Thermal equilibrium: ________

Definitions INTERNAL ENERGY  or (heat energy of any substance): The molecules of every substance, whether solid, liquid or gas are in perpetual motion. If heat is supplied to a substance, the motion (the vibration) of its molecules increases as its temperature rises. The kinetic energy of the molecules therefore increases. Thus heat is a form of energy. Thermal contact: -when heat gets transferred between objects that are in contact Thermal equilibrium :-when two objects at different temperatures come into contact and heat gets transferred to the cooler object such that there is no more temperature difference.

Question You heat a half cup of tea and its temperature rises by 40C. How much will the temperature rise if you add the same amount of heat to a full cup of tea? When a hot object cools down, where does the energy go?

Answer By 20C The energy is used to heat up the surrounding.

Questions True or false? Internal energy is the sum total of potential and kinetic energy of the individual particles of a body.____ Heat content of a body is the same as temperature.____ Heat content of a body is always transferred._____

Measuring heat calorie: This is the amount of heat required to raise the temperature of 1 gram of water by 10C. Kilocalorie is 1000 calories: - is heat required to raise 1 kg of water by 10C. Calorie ( with capital ‘C’)- the Food unit is actually a Kilocalorie

units of heat 2. Joule: this is the SI- Unit of heat. converting calorie to joule 1 calorie = 4.184 joules 1 kilocalorie = 4184 joules.

Specific heat Capacity Specific heat capacity is the quantity of heat required to raise the temperature of a Unit mass of a substance by 1º C Specific heat capacity of water is : calories Joules For 1 gram of water 1 cal/g0C 4.184 J/g0C For 1kg of water 1000 cal/kg0C 4184 J/kg0C

Specific Heat Capacity at 25oC in J/goC Substance Specific Heat Capacity  at 25oC in J/goC Hydrogen gas 14.267 Helium gas 5.300 water 4.184 lithium 3.56 ethyl alcohol 2.460 ice at 0oC 2.010 steam at100oC vegetable oil 2.000 air 1.020 magnesium aluminum 0.900 Concrete 0.880 glass 0.840 potassium 0.75

What is needed to quantify amount of heat The factors to consider when quantifying the amount of heat transferred into a substance are: Mass (m), Change of temperature (ΔT), and Specific heat capacity ( c ). Quantity of heat Q = mc ΔT

Example Calculate the amount of heat required to raise 1 kg of water by 45º C. a) In joules, b) In calories. Soln: Q = mc ΔT a) Q = 1 x 4184x 45 = __________ b) Q = 1 x 1000 x 45 = __________

Class work/ Homework Textbook pg 322 # 6-12 Textbook Page: 323 # 19-24

Thermal expansion Linear expansion: change in length = (original length) • (coefficient of expansion)• (change in temperature) Example: If a 20 cm iron rod whose coefficient of expansion is 12 x 10-60/C is heated to a temperature of 400C from room temperature of about 230C, What is its change in length?

Heat Lost = Heat Gained Heat Lost = Heat Gained Whenever two substances at different temperatures and mixed, the hot one cools down while the cold one warms up. However; Heat Lost = Heat Gained

Example: What would be the final temperature if you mixed 3 liters of water at 300C and 2 liters of water at 500C?

Class work Textbook Page 324, # 40-48,

Solve problems Purpose: Solve problems on specific heat capacity. Objective Use the formula for quantity of heat Q = m · c · ΔT to solve problems on heat. Use the concept of heat lost by an object = Heat gained by another object to solve heat problems.

Why do athletes cover themselves with some warm clothing after an event even though their chests are burning up? What is the heat lost by a 500 ml (500 g) water at 100º C when put in a fridge at 15º C? Specific heat capacity of water is 4.184 J/g·º C.

Class work: Workbook pg 144 exercises 8 –11 Page 147 # A8-A10