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Chapter 1, Lesson 5 Multimedia

Air Has Mass, Basketball

A deflated basketball is placed on a scale. Its mass is recorded. Next, air is pumped into the ball until it is fully inflated. The ball is weighed again, and the mass has increased. This shows that air has mass.

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  • The deflated basketball has a mass of 576 grams.
  • After adding air, the inflated basketball has a mass of 581 grams.
  • Therefore, the mass of the air added was 5 grams.

Air Has Mass, Can

A can of compressed gas is placed on a scale. Its mass is recorded. Next, air is released from the can by depressing the trigger. When the can is placed back on the scale, its mass is less than it was before. This shows that air has mass.

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  • The can of compressed gas has a mass of 135 grams.
  • After letting gas out of the can, it has a mass of 132 grams.
  • Therefore, the gas that escaped had a mass of 3 grams.

Particles of a Gas

A closeup on the particles of gas inside a balloon. The particles are spread very far apart and move around very rapidly.

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  • The particles (atoms or molecules) of a gas have very little attraction for one another.
  • They barely interact with each other. If they collide, they usually just bounce off.
  • The particles of a gas are much further apart than the particles in a liquid or a solid.

Heating and Cooling Gas in a Bottle

A thin bubble layer is covering the mouth of a plastic bottle. When the plastic bottle is placed in hot water, the “bubble” grows outward from the mouth of the bottle. When the bottle is placed in cold water, the bubble decreases in size.

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  • The red arrows in the animation represent outside air pushing down on the bubble film.
  • When the bottle is heated, the molecules inside the bottle move faster, the faster moving molecules inside the bottle push against the bubble film, and this push from the inside air overcomes the push from the outside air, forming a bubble.
  • When the bottle is cooled, the molecules inside the bottle move slower, the slower moving molecules inside the bottle push less hard against the bubble film, and the outside air overcomes the push from the inside air, forcing the bubble down.

Comparing Solids, Liquids, and Gases

A comparison of the molecules in a solid, liquid, and gas. Molecules in a solid are in fixed positions, but do vibrate. In a liquid, they feel an atraction for another but can slide past each other. In a gas, they have a lot of movement, and associate with one another far less.

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  • The molecules shown are from three different substances that are all at room temperature.
  • In the solid, molecules are strongly attracted to one another they vibrate but do not move past one another, and molecules stay in fixed positions because of their strong attractions for one another. A solid has a definite volume and a definite shape.
  • In the liquid, molecules are attracted to one another, molecules vibrate but are also able to move past one another, a liquid has a definite volume but does not have a definite shape.
  • In the gas, molecules are not attracted to each other much at all. The molecules in gas vibrate and are also able to move freely past each other. A gas does not have a definite shape of volume. Gas molecules will spread out evenly to fill any container.

Solid, Liquid, and Gas

In solids, the molecules have the least movement, vibration, and are close together in fixed positions.In liquids, molecules have more more movement and can slide past each other.  In gases, the constituent molecules have the most movement, and are greatly spead apart.
  • In a solid, the particles have strong attractions, orderly arrangement, and are close together. Solids have a definite volume and shape.
  • In a liquid, the attractions between particles are not as strong as in solids. They are randomly arranged and slightly further apart. Liquids have a definite volume, but not a definite shape.
  • In a gas, the particles are arranged randomly, are very far apart, and the attractions between them are weak. Gases have no definite volume or shape.

Heating Molecules of a Gas

A closeup on the particles of gas inside a balloon. As the temperature of the particles inside the balloon is raised, the volume of balloon increases because the particles strike the elastic balloon boundaries with greater force. As the temperature is cooled, the volume of the balloon decreases as the molecules strike the elastic boundary with less force.

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  • The molecules of a gas have very little attraction for one another and so barely interact with each other.
  • When the molecules of a gas are heated, they move faster.
  • The faster moving molecules inside the balloon push against the material the balloon is made out of.
  • This push from the inside air overcomes the inward pull of the balloon, making the balloon get bigger.