Daily Science pg. 40

1
Daily Science pg. 40

• Convert the following temperatures
• 45oC into Kelvin
• 45o C into Fahrenheit
• 309 K into Fahrenheit
• 98oF into Kelvin
• 299 K into Celsius
• 8oF into Kelvin
• Give an example of conduction, convection, and
  radiation. Explain why over exposure to the sun
  or to X-rays can be harmful.
• Calculate the kinetic energy of a wheel that has
  a mass of 65 kg and is rolling with a velocity of
  4.5 m/s.
• Calculate the potential energy of a bomb that is
  falling from a height of 48 m and has a mass of
  15 kg.
• Calculate the potential energy of a ball dropped
  from E-wing that weighs 4.8 N and is being
  dropped 6 m.
• Calculate the mass of a person in a wheelchair if
  they are rolling at a velocity of 0.7 m/s and
  have 20 j of kinetic energy.

2
Specific Heat

• Pg. 41

3
Conductors and insulators

• Conductor- a material through which energy can be
  transferred as heat.
• Examples
• Insulator- a material that transfers energy
  poorly.
• Examples

4
Specific Heat

• The amount of energy needed to change the
  temperature of a substance by a certain amount is
  what determines if a substance will be a good or
  poor conductor.
• Specific heat is the quantity of heat needed to
  raise the temperature of 1 kg of substance by 1
  K.
• Specific heat is a physical property.

5
Specific heat values

• Every substance has a unique specific heat.
• The letter C is used to denote specific heat.
• Water has one of the highest specific heat values
  (4,186 J/kg x K)

6
Calculating Specific Heat

• Heat mass x temperature change x specific heat
  value
• Q m x ?T x C
• Units
• Mass-
• Temperature-
• Specific Heat-
• Heat-

7
Practice Problems

• How much energy is needed to increase the
  temperature of 0.755 kg of iron from 283 K to 403
  K?
• How much energy must a refrigerator absorb from
  225 g of water to decrease the temperature of the
  water from 35oC to 5oC?

8
State changes

• Heat makes objects change state.
• Energy of a substance either raises the
  substances temperature or changes the
  substances state. NOT BOTH AT THE SAME TIME.
• This is why there
• are horizontal lines
• on a phase change
• diagram.