Section 2-2 Teaching Outline

Book K

Anticipatory Set

Discover: Creating Soap Bubbles

Items used: Purchase bubble soap

Loops for making the bubbles

Procedure: See page 50 k TE

Assignment:

Assign Reading

Go over reading hints p. 49K

Objectives: The student will be able to…

Activating Prior Knowledge: What happens to how a bike tire feels as we pump it up? What if we don’t pump it up enough. What if we fill it up too high?

Presentation: (Blow up a balloon)

Measuring Gases: There are several difficulties in dealing with gases. What do you think they may be? Invisible, always moving.

How do we know how much gas is in a balloon?: This is hard to say because gases can be compressed into tiny areas. A helium tank could fill 100"s of balloons at much greater volumes.

What is volume? The amount of space an object takes up. A gas however fills up whatever space there is. It’s volume can change to meet the size of any container.

What is temperature? How hot an object is? It is how much energy the particles of a substance has. (the solar wind has particles thousands of degrees, but we could stand in it and not be burned) The particles are very wide spread but very high energy.

EX: at room temp 20’C gas particles travel at 500m/s these may be steam particles from a boiling pot at the other end of the room, very hot but not enough of them to burn you.

Pressure: As particles zoom around the room they bump into things and push on them, This is called pressure. The more particles pushing against the sides or the faster they push the greater the pressure. Kilopascals

Force (N)

(kPa) Pressure = Area (cm2)

So how do we increase the pressure in a tire?, put in more particles and then more of them push on the sides.

Why does a tire go flat if air is pushing on the outside too, couldn’t a balloon fill up?

Because more particles are hitting the hole form the inside than out. Pressure always goes form high to low even though movement goes both ways. When it is flat particles go in and out at the same rate.

What are three properties of gases that we can measure? Temperature, Pressure and Volume

Relating Pressure and Volume

EX: Take a large syringe seal the end and push on it. The air volume in it decreases. What happens to the pressure that is needed to push it? It increases greatly. What can we say in general then if we decrease the volume of a gas? Pressure increases.

Indirect Relationship: As volume decreases pressure increases.

Robert Boyle Discovered this in the 1600s and developed Boyle’s law

Boyle’s Law: When the pressure of a gas increases, its volume decreases. When the pressure of a gas decreases, the volume increases.

EX: Tell students to bring in a bag of miniature marshmallows and we will put them in syringes to see the effect of gas pressure.

Pressure and Temperature: p. 52K

We talked about how particles have temperatures, or energy.

Temperature and Energy

Solid objects are frozen and have very little particle energy so the particles stay in place .

Liquid objects have slightly more energy and their particles can flow but cannot escape the liquid.

Gaseous objects have even more energy they have enough to escape the pull of other particles and to fly through the air. As we increase the temperature of a gas the particles move even faster.

They begin to run into things at very high speeds. Remember that the push against the wall of a container is pressure. So as temperature increases what happens to the pressure in a container?

EX: Helium Balloons in the winter. If outside you bring them in and they sink towards the floor as they warm they float higher in the room.

DEMO: Solar bag measure volumes etc. (Have them feel the bag at first then as it warms to determine relative pressure.

Direct Relationship: As temp increases pressure increases as temp decreases pressure decreases.

Charles’s Law: Jacque Charles late 1700’s

DEMO: Temperature decrease with a tin can. As temp goes down the can cannot push out to the sides and the outside pressure crushes it.

Check Your Progress:

Group Projects. P. 55 K

Activity at Home: Round Balloon Tape and a Freezer. Blow up a balloon and measure it’s volume with a string or metric tape. Put the balloon in a freezer overnight and re-measure the volume. Calculate the amount of volume lost.