Identifying Variables &Identifying Variables &Designing Designing

InvestigationsInvestigationsin the Scientific in the Scientific

Method.Method.Physical SciencePhysical Science

3 Kinds of Variables in Physical 3 Kinds of Variables in Physical ScienceScience

Independent Variable – something that Independent Variable – something that is changed by the scientistis changed by the scientist What is testedWhat is tested What is manipulatedWhat is manipulated What is controlledWhat is controlled Example: Ohm’s law : U = I x RExample: Ohm’s law : U = I x R

Something else?Something else?

3 Kinds of Variables in Physical 3 Kinds of Variables in Physical sciencescience

Dependent Variable – something that Dependent Variable – something that might be affected by the change in the might be affected by the change in the independent variableindependent variable What is observedWhat is observed What is measuredWhat is measured The data collected during the investigationThe data collected during the investigation

3 Kinds of Variables in Physical 3 Kinds of Variables in Physical sciencescience

Controlled Variable – a variable that Controlled Variable – a variable that is not changedis not changed Also called constantsAlso called constants Allow for a “fair test”Allow for a “fair test” Any example we know in Physical Any example we know in Physical

Science?Science? What about Newton’ laws?What about Newton’ laws?

Let’s look for several exa- Let’s look for several exa- mples for Physical Sciencemples for Physical Science

First Example we have isFirst Example we have isin Physical science:in Physical science:

Wires of different Wires of different resistances R were given resistances R were given the same voltage V in a the same voltage V in a

closed circuit. closed circuit. So what is changing?So what is changing?

The current I? Remember The current I? Remember the formula! V = I x R.the formula! V = I x R.

Now remember the very Now remember the very important step in our important step in our

investigation!investigation!Let’s identify the variables Let’s identify the variables

in this investigation.in this investigation.

What was the independent What was the independent variable?variable?

resistances of the wiresresistances of the wiresDifferent resistances were tested by Different resistances were tested by

the scientistthe scientistRemember that voltage was fixed Remember that voltage was fixed

and thus constant!and thus constant!So what is changing then? So what is changing then? Of course, the current!Of course, the current!

What was the dependent variable?What was the dependent variable?

The current!The current!The current was observed and The current was observed and

measured by the scientistmeasured by the scientistAgain the formula of the Ohm’s law Again the formula of the Ohm’s law

is V = I x Ris V = I x RV is voltage, I is current, R is V is voltage, I is current, R is

resistanceresistance

What was a controlled variable?What was a controlled variable? Devices we used to measure:Devices we used to measure: AmpermeterAmpermeter VoltmeterVoltmeter OhmmeterOhmmeter MultimeterMultimeter

Something else?Something else?

Are you getting the idea?Are you getting the idea?Or not!?!Or not!?!

Another example in the Another example in the Physical Science:Physical Science:

An investigation was done with An investigation was done with an electromagnetic system made an electromagnetic system made from a battery and wire wrapped from a battery and wire wrapped around a nail. Different sizes of around a nail. Different sizes of nails were used. The number of nails were used. The number of

paper clips the electromagnet paper clips the electromagnet could pick up was measured.could pick up was measured.

What are the variables in this What are the variables in this investigation?investigation?

Just be careful!Just be careful!But give your opinions!?But give your opinions!?

Go!Go!Please!Please!

Can we do it!?Can we do it!?

Independent variable in Independent variable in Physical Science:Physical Science:

Sizes of nails. Why?Sizes of nails. Why?Just because -Just because -

These were changed by the These were changed by the scientist. He can pick up scientist. He can pick up anything he likes! anything he likes!

Can he?!Can he?!

Dependent variable:Dependent variable:

Number of paper clips picked Number of paper clips picked up (by what?) - magnetup (by what?) - magnetThe number of paper clips The number of paper clips

observed and counted (by observed and counted (by whom? (measured) (by whom?)whom? (measured) (by whom?)

What is your answer?What is your answer?

Controlled variables:Controlled variables:

Battery, wire, type of nailBattery, wire, type of nail None of these items were changedNone of these items were changed

REMEMBER WHAT IS UNDER CONTROL?REMEMBER WHAT IS UNDER CONTROL?

WHAT ELSE IS NOT CHANGING?WHAT ELSE IS NOT CHANGING?

Let’s go to one more Let’s go to one more example in Physical example in Physical

science!science!

The higher the The higher the temperature of water, temperature of water, the faster an egg will the faster an egg will

boil?!boil?!ARE YOU SURE ARE YOU SURE ABOUT THAT?ABOUT THAT?

SHALL WE CHECK?SHALL WE CHECK?

WHAT WE HAVE IN THIS WHAT WE HAVE IN THIS INVESTIGATION?INVESTIGATION?

Let’s see:Let’s see: Independent variable – temperature Independent variable – temperature

of waterof water Dependent variable – time to cook Dependent variable – time to cook

an eggan egg Controlled variable – type of eggControlled variable – type of egg

Last example for today in Last example for today in Physical Science:Physical Science:

Remember the previous Remember the previous examples?!examples?!

What did you get from What did you get from those examples?!those examples?!

Any idea?!Any idea?!

The temperature of The temperature of water was measured at water was measured at

different depths of a different depths of a pond.pond.

LET’S SUMMARIZE OUR LET’S SUMMARIZE OUR RESULTS:RESULTS:

Independent variable – depth of the Independent variable – depth of the waterwater

Dependent variable – temperatureDependent variable – temperature Controlled variable – thermometerControlled variable – thermometer

THIS IS A VERY IMPORTANT THIS IS A VERY IMPORTANT We are designing InvestigationsWe are designing Investigations

Basically we plan and do the Basically we plan and do the steps of work to accomplish our steps of work to accomplish our

final goal!final goal!Which was what?!Which was what?!

Now do you see how all is Now do you see how all is connected and important?!connected and important?!

The greater the amount of soap in a The greater the amount of soap in a soap and water mixture, the bigger a soap and water mixture, the bigger a

soap bubble can be blown.soap bubble can be blown. Design an investigation to test this hypothesis.Design an investigation to test this hypothesis.

Identify the variablesIdentify the variables What exactly will be changed? How will it What exactly will be changed? How will it

be changed?be changed? What exactly will be measured? How will it What exactly will be measured? How will it

be measured?be measured? WRITE IT AS A HOMEWORK!WRITE IT AS A HOMEWORK!

The farther a ball drops, the higher The farther a ball drops, the higher it will bounce.it will bounce.

Design an investigation to test this Design an investigation to test this hypothesis.hypothesis. Identify the variablesIdentify the variables What exactly will be changed? How What exactly will be changed? How

will it be changed?will it be changed? What exactly will be measured? How What exactly will be measured? How

will it be measured?will it be measured? WRITE IT AS A HOMEWORK !WRITE IT AS A HOMEWORK !