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Which of the following is an example of how a scientist might use a model?

• A microscope is used to magnify a group of cells on a slide.

• The end of a slinky is moved vertically up and down to simulate a wave.

• A wrench is used to tighten a nut onto a piece of wood.

• A stopwatch is used to time the rate of a chemical reaction.

Which of the following is an example of how a scientist might use a model?

• Microscopes are used to magnify a group of cells on sets of slides.

• Stopwatches measure the amount of time it takes for runners to complete a mile.

• A wrench is used to tighten a nut onto a piece of wood.

• Marbles placed inside a hollow sphere are used to describe protons in a nucleus.

No system is completely closed off from its surroundings. Which represents a system that is almost completely closed?

• a washing machine

• a wood-burning fireplace

• a capped soda bottle

• a pot of boiling water

Which best explains why a wood-burning fireplace represents an open system?

• because they are not all made of brick

• because they can be used for cooking

• because the ashes have to be swept away because

• because a fire requires oxygen from the atmosphere to burn

Which best explains why a washing machine represents an open system?

• Water and power come from external sources.

• The amount of wash in a load varies

• It has multiple cycles, such as wash and spin.

• Most washers can use a variety of laundry detergent brands.

Which of the following represents a system that is completely open?

• a pressure cooker

• a pressurized canister of helium gas

• a pot of boiling water

• a capped soda bottle

Why is the law of gravity an example of a universal law?

• Gravity is the attraction of any mass to any other mass.

• Gravity is a force that affects everyone on Earth

• Gravity is the reason the Earth revolves around the sun.

• Gravity is a force that exists between any two masses in the universe.

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Which statement best defines a universal law?

• It is in effect at all times.

• It operates only under specific conditions.

• It is in effect some of the time.

• It changes over time.

The model of the atom has changed over time in light of new knowledge and discoveries. Which option correctly describes one such change?

In 420 B.C., John Dalton developed the idea that small atoms combined to form molecules.

• In 420 B.C., John Dalton developed the idea that small atoms combined to form molecules.

• About 1900, Neils Bohr developed an atomic model where positively charged particles orbit a negatively charged nucleus.

• About 1900, J.J. Thomson discovered electrons were negatively charged particles.

• About 1915, J.J. Thomson developed an atomic model where negatively charged particles orbit a positively charged nucleus.

Our understanding of the atom has changed over time. Which idea that was once accepted is now considered scientifically inaccurate?

• The nucleus is the center of the atom.

• An atom is a solid sphere

• Electrons have a negative charge.

• Electrons are arranged in layers.

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