Tell the person next to you...· Imagine pushing a king sized bed from one side of the classroom to the other· Would it make you feel tired?o Yup!· Would you have to work hard to push it?o Yup!· What could you change so you have to do less work pushing?o Anything that decreases the force needed (reduce friction by putting wheels on it, ice under it, etc)o Anything that decreases the distance travelled (only push it half way!, etc)o So the formula for work must contain force and distance
Friday, September 9, 2011
Starter - answers
Monday, September 5, 2011
Plenary Questions
PFY p.54
1
a) Thermal energy travels through the bottom of a pan by convection. The energy is passed from one vibrating atom to the next. All metals are good conducts. Plastic, water and air are poor conductors (good insulators)
b) Convection currents can form when liquids and gases are heated. The cold fluid falls and the hot fluids rises.
c) Energy can travel through empty space by radiation rays, which can be reflected by mirror like light rays. Dull black surfaces are good radiators and good absorbers. Shiny, bright surfaces are good radiators and bad absorbers.
d) A vacuum flask uses silvering to cut down heat transfer by conduction and uses a vacuum to cut down heat transfer by convection and radiation.
4.8
·4.8 describe how insulation is used to reduce energy transfers from buildings and the human bodyTask 1
· Use this interactive animations to investigate how different insulation affects the rate of cooling of hot water<<Cooling of hot water with insulation - interactive.swf>>Task 2
· Use these interactive animations to find out about the energy transfers in a house
Task 3
· Test your knowledge with this quiz<<Quiz - Types of energy transfers in a house.swf>>
Saturday, September 3, 2011
Monday, August 29, 2011
Answers to Entrance Activity for 4.7
Answers...
1. What is the most common heat transfer mechanism in solids?
Conduction
2. What is the most common heat transfer mechanism in liquids and gases?
Convection
3. What is the only heat transfer mechanism in a vacuum?
(Infra-red) Radiation
4. Why can't conduction happen in a vacuum?
There are no particles in a vacuum to transfer the vibrations
5. What happens to the space between the particles in a gas when you heat it?
The space between the particles increases
6. What happens to the density of a gas when you heat it?
It decreases because the space between the particles increases
7. Why can't convection happen in a solid?
In a solid the particles are fixed in position and are not free to move
Sunday, August 21, 2011
4.6 - Recall that energy transfer may take place by conduction, convection and radiation
4.6 recall that energy transfer may take place by conduction, convection and radiation Task 1
· Try the animation: particle model - conduction
· Extension: what is the limitation of this animation? (Check your answer with the Heating a Solid animation) The limitation is that the animation does not show that the object expands when it is heated.
Task 2
· Try the quiz on the Cooking animation
· Extension: what's the mistake in the description of convection? The animation states that the molecules at the bottom of the liquid heat up and they start to rise, when they cool down the molecules shrink again and sink. This creates a convection current and gradually all of the liquid heats up. This is wrong because if you heat a liquid from below, the liquid at the bottom gets heated up and it expands. The liquid then rises because it has a lower density, afterwards the cool liquid (at the top) sinks to the bottom where the heat source is and it then expands and rises. The process is repeated. This is called convection current.
· Try the animation: particle model - conduction
· Extension: what is the limitation of this animation? (Check your answer with the Heating a Solid animation) The limitation is that the animation does not show that the object expands when it is heated.
Task 2
· Try the quiz on the Cooking animation
· Extension: what's the mistake in the description of convection? The animation states that the molecules at the bottom of the liquid heat up and they start to rise, when they cool down the molecules shrink again and sink. This creates a convection current and gradually all of the liquid heats up. This is wrong because if you heat a liquid from below, the liquid at the bottom gets heated up and it expands. The liquid then rises because it has a lower density, afterwards the cool liquid (at the top) sinks to the bottom where the heat source is and it then expands and rises. The process is repeated. This is called convection current.
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