Models and Systems

Lesson 1.4Chapter 1: Using Scientific Inquiry

Interactive Science Grade 8, Pearson Education Inc., Upper Saddle River, New Jersey

Objectives

• Explain how models are used in science.• Describe different types of systems, and

identify characteristics that all systems share.• Examine models of natural systems, and

compare the model to the system itself.

I. How Do Scientist Use Models?

• Scientists use models to test ideas about things they cannot observe directly.– Model – any representation of an object or a

process.– Types of models:• Physical• Mathematical• Computer

• Models can be used to represent systems.

Bohr Model of Hydrogen Quantum Mechanical Model of Hydrogen

II. What Are the Characteristics of a System?

• All systems have at least one input, at least one process, at least one output.

How Toasters WorkMost electric pop-up toasters all operate in the same manner. A slice of bread, a frozen waffle, a toaster strudel, or some similar food item is placed through a slot in the top of the toaster and into the carriage. The carriage is lowered into the chassis using the lever at the side of the toaster.When it reaches the bottom, the carriage latches in position and an internal switch is activated to start the heating process. A thermostat determines how long electric current will be sent from the power cord to the heating elements.The person who is operating the toaster sets the thermostat using a control knob or lever calibrated between light and dark. When the desired temperature is reached and the heating process is completed, the solenoid turns the current off, then unlocks the latch and allows the carriage to spring up to its original position. At this time, the toasted food is easily reachable and can be removed by the operator of the appliance.

• System – a group of parts that work together to carry out a function.– Examples: bicycle, toaster, flashlight, human body.

• Input – material or energy that goes into a system.

• Process – action or series of actions that happen within a system.

• Output – material or energy that comes out of a system.

• All systems have feedback, output that changes the system in some way.

III. How Do Models Help Scientists Understand Systems?

• Scientists build models to represent a process. They test whether the input and output from the model match the input and output of the system in the natural world.– Help to understand the process.– Can be used to predict changes in a system as a

result of feedback or input changes.

• Modeling Simple and Complex Systems– Some system are simple, just a few parts or steps

in the process.– Some, complex with many parts and variables, or

factors that vary.• Example: weather systems• Because complex systems are difficult to model,

scientist may model only the part of the system they want to study.

• Testing Assumptions– Models have assumptions• Example: a planet must have water to support life,

– Scientist check their assumptions• Compare input and output of models to the input and

output in the natural world.– If they match, assumptions are supported.– If not, assumptions must be changed.

– Some assumptions are used to simplify a model.• Example: a food chain is a simplified model of energy

flow in an ecosystem.

• Advantages and Limitations of Models– Models help us understand how systems work.– Models help us understand processes and how a

system might change when factors are manipulated.

– However, models may be limited and not include all the parts of a process.• Example: Even a food web does not show all the

interactions in an ecosystem.