heat in the environment mr. williams – grade 7 science part 1

Heat in the EnvironmentMr. Williams – Grade 7

SciencePart 1

So what are we going to learn?

• By the end of this unit, you will be able to identify and understand the following concepts:– Heat is a form of energy that can be

transformed and transferred. • This process can be explained using the particle

theory.– There are many different sources of heat– Heat has both positive and negative effects

on the environment.

Warm and Cold• All living things are

sensitive to warmth and coldness.

• Humans are able to keep warm by wearing clothes, burning fossil fuels and performing physical activities.

• Snakes and lizards need to sit in the sun to absorb the suns rays in order to obtain their warmth

Warm and Cold Cont’d

• However, animals and humans also avoid excessive warmth because it is dangerous to health.

• Animals and other mammals that overheat can suffer damage to their internal organs and can even die.

• So…many species develop or have innate methods to manage heat. For example:

• Dogs pant to keep cool• Bee’s flap their wings• Humans use air conditioners!!!

Heating and Cooling Buildings• It is not easy to keep homes cool in the summer

and warm in the winter months, especially in the climate of Ontario.

• That is why we rely on the use of HVAC (Heating, ventilation and air conditioning)

• Most Ontario homes are built with central heating systems and air conditioners. These systems typically burn fossil fuels like petroleum and natural gas. Why might this become a problem in future years?

• Did you know…In ancient Rome, the people use to sometimes cool their homes by running river water through the walls!!! Now that’s cool!

HVAC Cont’d

Wood, oil, coal and natural gas release energy and gases as waste when they burn. Some of these gases are toxic and must be removed from the building. Chimneys carry these gases out of the home.

Checkpoint

1. Give 2 examples of how animals keep themselves warm or cool.

2. Give an example of how people keep themselves warm and cool.

3. Why do buildings have chimneys?4. Why should we try to use less oil, natural gas

and electricity?

Ha Ha…Burn!

Explaining Hot and Cold

• We use the word “heat” a lot to describe warmth, but what is heat?

• Well, in the early 1800’s, scientists suggested that warmth was caused by the motion of small particles that make up matter. The faster the particles move, the warmer it feels. – This concept became part of the Particle Theory of Matter!

• All matter is made up of tiny particles• Particles have spaces between them• Particles are always in motion• Particles move faster when they are heated• Particles attract each other

Heat

• When an object is heated, its particles move faster. When an object is cooled, its particles move slower.

Heat – the transfer of energy from the particles of a warmer object to the particles of a cooler one.

• When a warm object comes into contact with a cold object, the faster-moving particles bump into the slower moving particles. As result, energy is transferred!

• Learning Point: Heat is not absorbed by a substance.– For example, water can not absorb heat, it absorbs the energy.

Kinetic Energy, Heat and Temperature

• Warmth and coldness always refer to the movement of particles, and because we know that particles are always moving, the particles of matter posses an energy called kinetic energy!

• Although all particles of matter are attracted to one another, they never stop moving.

• All particles are moving at different speeds, similar to that of bumper boats at an amusement park.

Kinetic Energy Cont’d

• Due to all of the different particles moving at different speeds, we know that all particles have different amounts of kinetic energy.

Kinetic Energy – Energy that all moving objects posses. A particle has more kinetic energy when it is moving faster and less kinetic energy when moving slower.

• Particles of matter also move and collide randomly, some speeding up and some slowing down.

Examples of Kinetic Energy

Potential and Kinetic Energy

Temperature• Hot objects have particles moving faster than cooler

objects. Therefore, the average kinetic energy is higher in the hotter objects than in the colder.

Temperature – Is a measure of the average kinetic energy of the particles of a substance.

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. Changes in thermal energy can also cause a substance to change state.

Changes in States of Matter

Thermal Expansion and Contraction

• When solids, liquids and gases are heated, their volumes usually increase. This is called thermal expansion.

• When solids, liquids and gases are cooled, their volumes usually decrease. This is called thermal contraction.

• Cooling a substance slows down its particles because they have less energy. This means that they take up less space!– Remember, there is no change in mass or volume because we

are adding particles. The difference is the SPACE in between the particles is changing!

Checkpoint

Review the Particle Theory and the States of Matter on pg.188

Answer the check your learning questions on the bottom of pg.189 (all)