Describing the Describing the Physical Physical UniverseUniverse

Chapter 1 Section 2Chapter 1 Section 2Distance and TimeDistance and Time

Measuring Measuring DistanceDistance•What is a measurement?What is a measurement?•A A measurementmeasurement is an is an exact value that tells you exact value that tells you “how much”.“how much”.

•It is important that a It is important that a measurement can measurement can communicate an amount communicate an amount in a way that other in a way that other people can understand.people can understand.

4545•Is this a measurement?Is this a measurement?•It is not a measurementIt is not a measurement•Are we talking about Are we talking about apples or kiwis?apples or kiwis?

MilesMiles•Is this a measurementIs this a measurement•This is not a measurementThis is not a measurement•Is there half a mile or 100 Is there half a mile or 100 miles?miles?

•Every good measurement Every good measurement gives a quantity and a unit.gives a quantity and a unit.

• A A unit of measurementunit of measurement is a is a standard amount of a standard amount of a quantityquantity

•What separates a good unit What separates a good unit from a bad unit?from a bad unit?

•ActivityActivity•Directions: Directions: •Part 1: One at a time, Part 1: One at a time,

everyone take your right everyone take your right hand and measure how hand and measure how many “hands” it takes to go many “hands” it takes to go around one lab bench.around one lab bench.

•1 hand is from the tip of your 1 hand is from the tip of your longest finger to the bottom longest finger to the bottom of your palm.of your palm.

•Part 2: Using your own feet, Part 2: Using your own feet, measure how many feet it measure how many feet it takes to get from the teachers takes to get from the teachers desk to lab station 5.desk to lab station 5.

Put your results Put your results on the board.on the board.

•Before measurement was Before measurement was standardized, the king standardized, the king where you were living where you were living would make measurements.would make measurements.

•A foot was how long the A foot was how long the kings foot was.kings foot was.

•A cup was how much water the A cup was how much water the kings favorite cup could hold.kings favorite cup could hold.

•Now imagine living in medieval Now imagine living in medieval France, and the king of Spain France, and the king of Spain ordered 500 cups of wine. How ordered 500 cups of wine. How could this cause a problem?could this cause a problem?

•DistanceDistance is the amount of is the amount of space between two points.space between two points.

•The space between you and The space between you and your friend, or the space your friend, or the space between your house and the between your house and the school are all distancesschool are all distances

•Distance is measured in Distance is measured in unites of unites of length.length.

•Some examples of length Some examples of length are inches, miles, are inches, miles, centimeters or kilometers. centimeters or kilometers.

Two Systems of Two Systems of MeasurementMeasurement

•These two systems are These two systems are called the called the English SystemEnglish System and the and the metric systemmetric system..

Only 3 countries in the world Only 3 countries in the world still use the English systemstill use the English system

Liberia, Myanmar, and USA

•Another name for the metric Another name for the metric system is the International system is the International System of UnitsSystem of Units

•This can be abbreviated to SIThis can be abbreviated to SI•Almost all of science is Almost all of science is measured using SI units.measured using SI units.

•This is because everything This is because everything is measured in factors of 10.is measured in factors of 10.

•1 kilometer = 1,000 meters1 kilometer = 1,000 meters•1 meter = 100 centimeters 1 meter = 100 centimeters = 1000 millimeters= 1000 millimeters

•In this class, we will be In this class, we will be using the metric system using the metric system the most often but will the most often but will occasionally use the occasionally use the English system.English system.

Measuring TimeMeasuring Time•The word time can have The word time can have two meanings.two meanings.

•It can be an exact moment It can be an exact moment or it can be a duration.or it can be a duration.

•When you ask for the When you ask for the time, you want to know an time, you want to know an exact moment.exact moment.

•You then proceed to You then proceed to identify this moment by identify this moment by checking a clock.checking a clock.

•You may also ask “how much You may also ask “how much time?”time?”

•For this you need a time For this you need a time interval.interval.

•A A time intervaltime interval is a quantity is a quantity of time that has a beginning of time that has a beginning and end.and end.

•In this class, time will In this class, time will mostlymostly be a time interval be a time interval and measured in seconds. and measured in seconds.

•Time is usually represented Time is usually represented by the variable by the variable tt

•The second is used in both the The second is used in both the English and metric system.English and metric system.

•Most often in physics, we will Most often in physics, we will time an event in seconds, but time an event in seconds, but sometimes we will have to sometimes we will have to consider a fraction of a second.consider a fraction of a second.

•How much time is 3:27:41?How much time is 3:27:41?•3 Hours, 27 minutes, and 3 Hours, 27 minutes, and 41 seconds41 seconds

•How many total seconds is How many total seconds is this?this?

•12461 seconds12461 seconds

•Most commonly people Most commonly people give time in mixed units.give time in mixed units.–Hours, minutes and secondsHours, minutes and seconds

•In science, the time can In science, the time can only have one unitonly have one unit–Usually secondsUsually seconds

Distance and Time Distance and Time GraphsGraphs

•If you want data on If you want data on something, a table of numbers something, a table of numbers can usually be provided.can usually be provided.

•However, organizing However, organizing these numbers into a these numbers into a graph will make them a lot graph will make them a lot easier to read.easier to read.

•You need two variables to You need two variables to make a line graph.make a line graph.

•The The independent independent variable variable is placed on the is placed on the x-axis (left to right)x-axis (left to right)

•We call it independent We call it independent because we can choose to because we can choose to take the measurement.take the measurement.

•The The dependent variabledependent variable is is placed on the y-axis (up and placed on the y-axis (up and down)down)

•We call it dependent We call it dependent because this variable because this variable changes according to the changes according to the independent variable.independent variable.