Grade 7 - Unit C

What are some things that keep us warm?

What are some items that cool us down?

Heating and Cooling - IntroductionIntroduction Are the people in this picture loosing heat and gaining cold? How do you know? How do you think you could find out?

Main Idea – How does heat affect matter?

Looking Ahead… Heating and cooling are important in the everyday process The particle theory related to heating and cooling Heat is the transfer of energy from warmer substances to cooler substances Most materials expand when they are heated and contract when they are cooled Investigation skills can be used to learn about expansion and contraction of different materials

Vocabulary Particle theory of matter Heat Kinetic energy Temperature Thermal energy Thermal contraction Thermal expansion

Heating Objects… What are some example of things we heat everyday? How does heating affect an object or material?

7.1 Warmth and Coldness What are some things that make us warm? Make objects warm? How do we keep warm in the winter? What are some things that make us cold? Make objects cold? How do we stay cool in the summer?

Does a fridge only make things cold?

How do these animals deal with heat? Some fly south during the winter Snakes and lizards bake in the sun to keep their bodies warm Honeybees flap their wings to cool their hives in hot weather

How do humans deal with heat? Dress in cool clothing Stay in air conditioned places Limit physical activity in the heat What happens when we get too hot?

Poor Insulation? Hot air leaks in Hot air leaks out Cold air leaks in Cold air leaks out Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Average temp (°C) –10 –9 – –7 How can we stop air from leaking in and out?

7.2 Explaining Hot and Cold What are the parts to the particle theory? How does the particle theory relate to a solid? How does the particle theory relate to a gas? How does the particle theory relate to a liquid?

Heat When an object is heated, the particles move faster When an object is cooled, the particles move slower Read top of page 186

Will they survive? Volunteers – ball demo Heat: is the transfer of energy from warmer things to cooler things

7.3 Kinetic Energy, Heat and Temperature DEMO – solid, liquid or gas? Why? How do slow movements affect the shape? How do fast movements affect the shape?

Kinetic Energy Energy that all moving objects possess; a particle has more kinetic energy when moving faster and less kinetic energy when moving slower Particles of matter bump and collide at different speeds (bumper cars)

Temperature A measure of the average kinetic energy of the particles of a substance The average kinetic energy of hotter particles is higher The average kinetic energy of colder particles is lower

The Particle Theory and the States of Matter Solids Liquids Gases

Solid The shapes and volumes of solids do not change because the particles vibrate The kinetic energy of particles is too low to overcome the forces holding the particles together The particles are packed close together, and are difficult to fit into smaller spaces

Liquid Take the shape of their containers and have a consistent volume The particles move faster than that of a solid There is still enough attraction between particles to keep them together but not tightly packed

Gas Expand fully in an empty container – volume and shape can change The fast motions of the particles prevent their forces of attraction from holding them close together Have very large spaces between them Easy to compress

The Particle Theory and Changes of State Thermal Energy: the total kinetic energy and energy of attraction of all the particles of a material we can increase the thermal energy of a substance by heating it We can decrease the thermal energy of a substance by cooling it Changes in thermal energy can cause a substance to change states (solid to liquid, etc.)

Changes of state involve changes of thermal energy… Condensation Evaporation Melting Freezing GAS LIQUID SOLID SUBLIMINATION DEPOSITION Increasing thermal energy of particles Decrease thermal energy of particles

Thermal Expansion When solids, liquids or gases are heated, their volumes increase The faster moving particles travel greater distances, so the occupy more space

Thermal Contraction When solids, liquids or gases are cooled, their volumes usually decrease The slower moving particles travel shorter distances, so they occupy less space Slows down the particles so they have less kinetic energy Read page 189

7.5 Living with Thermal Expansion and Contraction What ‘things’ in our daily lives are exposed to changing temperatures? What is the difference between thermal expansion and thermal contraction? Thermal expansion – get bigger Thermal contraction – get smaller

Expansion and Contraction of Solids What would happen to concrete if metal poles in the concrete expanded? The concrete would crack and the structure would be damaged How would you fix this? Put two solids together that can expand at the same rate Read page 192

Expansion and Contraction of Gases When gas is heated in a container, the particles are pressing against the walls of the container until it eventually breaks Example: filling a balloon with hot air until it eventually pops because it is too full and because of the heat Read page 193

Expansion and Contraction of Liquids Gasoline that is left in the vehicle tank on a warm day will expand Therefore you should always fill your gas tank when it is colder outside because you can get more in