Mr. Meles' Blog: May 2014

Friday, 23 May 2014

Review Links for Chapter 10

Thursday, 22 May 2014

Grade 7 Chapter 10 Test Dates

Classes 7B, 7C, 7D, and 7E have their Chapter 10 Test on Tuesday May 27th.

Class 7A has their test on Wednesday May 28th.

Wednesday, 21 May 2014

Chapter 10 Test Study Guide

Please study the following in order to be prepared for the test:

1. The Putt-Putt Boat

Review how a Putt-Putt Boat works
Identify energy transformations occurring during the running of the boat; e.g., chemical energy to thermal energy and light energy
Identify how thermal energy is transferred during the running of the boat i.e., conduction, convection, and radiation.
Identify changes of state occurring during the running of the boat e.g., evaporation

2. Energy Transformations e.g., electrical to mechanical

3. The 3 Methods of Thermal Energy Transfer i.e., conduction, convection and radiation. All the notes can be found on the blog.

4. The 6 Changes of State e.g., evaporation, condensation, etc.

5. Review worksheets on expansion and contraction of solids liquids and gases. All the answers can be found on the blog.

How Does the Putt-Putt Boat Work?

How does the putt-putt boat work?

When we heat the boiler with the candle, the water droplets inside the boiler evaporate; this causes expansion. A “click” can be heard as the boiler is pushed outward.

The expanding gas forces the water out of the straws; this propels the boat forward.

A partial vacuum is left inside the boiler; this is an area of low pressure compared to the atmospheric pressure outside. A “click” can be heard as the boiler is forced inward.

The higher atmospheric pressure forces water back into the straws and the engine which restarts the cycle.

This cycle repeats many times per second.

Additional reading can be found by following the link below:

http://www.sciencetoymaker.org/boat/howBoatWorksl.html

Thursday, 1 May 2014

Mr. Meles' Youtube Channel

You can find the Putt-Putt video playlist here. There are other interesting Science and Math videos here too!

https://www.youtube.com/user/TheMrMeles

Thermal Energy Transfer: Radiation

Radiation

· Radiant energy is the transfer of energy by invisible waves given off by the energy source

· These invisible waves are called infrared waves (a type of electromagnetic wave from the sun)

· Infrared waves are given off by all heat sources, including you

· Heat is radiant energy from the sun that reaches your skin

· Radiant energy warms up objects when the waves of radiant energy come into contact with matter making the particles vibrate faster

Answers to Radiation Worksheet

1) Radiation waves are absorbed by the person in front of you so you do not feel the heat.

2) White clothing reflects infrared radiation and black clothing will absorb this radiation.

3) The shiny suits will reflect the strong heat radiation from the sun so the astronauts do not overheat.

4) Insulation is a poor heat conductor and it contains glass pieces to reflect heat back into your home.

5) In summer, heat is reflected out into the environment and in winter, heat is reflected back into your home.

Thermal Energy Transfer: Convection

Convection

· Convection - The transfer of thermal energy by moving particles in fluids

· As the particles of fluids (gases and liquids) are heated, they move faster and expand; this expansion makes the fluids less dense so they rise

· When warmer fluids rise, cooler fluids move downwards; this creates a “convection current”

· The convection current continues in a pot of soup because the warmer soup particles in a pot cool when they make contact with the air and then sink. These particles are heated again once they meet the bottom of the pot.

· Convection currents help heat your home through your furnace heating system.

Thermal Energy Transfer: Conduction

Conduction

· The transfer of heat through a solid or between a solid and another solid, a liquid, or a gas that is in contact with it

· Conduction can also occur from liquid to solid and gas to solid.

· Conduction always occurs from a warmer region to a cooler region.

· Conduction occurs when warmer particles bump into cooler particles making them vibrate faster.

· Metals are better heat conductors than non-metals because free electrons carry heat quickly through the material.

Answers to Conduction Worksheet

On a cold winter day, why would an iron post in a park feel much colder to the touch than a wooden bench?

Iron is a better heat conductor than wood. The iron will conduct the heat away from your hand faster than wood; this makes your hand feel colder when you touch iron

Potatoes cook from the outside in.

a) Why does a small potato cook faster than a large potato?

Smaller potatoes have fewer particles, so heat takes less time to reach the centre.

b) Why does sticking a metal skewer through the middle of a potato make it cook faster?

Heat will be conducted through the skewer into the centre of the potato and it will cook from the inside out.

Mr. Meles' Blog

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