Moira Whitehouse PhD

MEASURING WEIGHTAND MASS

MEASURING WEIGHT

TO MEASURE MOST ANYTHING ONE NEEDS SOME TOOL WITH WHICH TO MEASURE AND A STANDARD UNIT OF MEASUREMENT.

•THE TOOL WE USE TO MEASURE WEIGHT IS A SPRING SCALE.

•THE STANDARD UNIT OF MEASUREMENT USED IN SCIENCE IS THE NEWTON.

•BEFORE SERIOUS TALK ABOUT THE SPRING SCALE, LET’S REVIEW THIS IDEA CALLED WEIGHT.•YOU SHOULD REMEMBER THAT THE WEIGHT OF AN OBJECT IS A MEASURE OF HOW HARD GRAVITY IS PULLING ON THE OBJECT.

•THE HARDER GRAVITY PULLS ON SOMETHING, THE MORE IT WEIGHS.

•WHEN WE PICK UP ANYTHING WE ARE WORKING AGAINST GRAVITY.

•IF WE FOUND OURSELVES ON THE MOON WHERE THE GRAVITY WAS LESS, WE WOULD SUDDENDLY SEEM TO BE A LOT STONGER.

•THE SPRING SCALE DOES THAT BY HAVING A SPRING THAT IS ADJUSTED TO BE JUST AS STRONG AS THE PULL OF EARTH’S GRAVITY.

•KNOWING THAT WEIGHT DEPENDS ON GRAVITY WE CAN SEE THAT ANY TOOL TO MEASURE WEIGHT MUSTSOMEHOW ACCOUNT FOR EARTH’S GRAVITY.

•THE PROCEDURE TO MEASURE WEIGHT IS TO SUSPEND THE OBJECT FROM A SPRING SCALE AND READ THE WEIGHT IN NEWTONS (n) FROM THE SCALE WINDOW.

TO MEASURE MOST ANYTHING ONE NEEDS SOME TOOL WITH WHICH TO MEASURE AND A STANDARD UNIT OF MEASUREMENT.

WE NEEDED TWO THINGS TO MEASURE WEIGHT, ONE WAS A TOOL

AND THE OTHER WAS:

•THE UNITS USED TO MEASURE WEIGHT IN THE METRIC SYSTEM ARE NEWTONS (n).

•SO WHAT IS THIS UNIT OF MEASUREMENT THAT IS NAMED FOR THE GREAT SCIENTIST ISAAC NEWTON? •LIKE OTHER UNITS IN THE METRIC SYSTEM, THE NEWTON IS DERIVED FROM THE METER

(ONE 10 MILLIONTH OF THE DISTANCE FROM THE NORTH POLE TO THE EQUATOR)

AND BY USING THE MASS OF WATER, THE EARTH’S MOST COMMON COMPOUND.

THIS MUCH WATER

EQUALS

1 GRAM

AND

IN EARTH’S GRAVITY

=X 100

= ONENEWTON

100 GRAMS

•WITH THAT BIT OF INFORMATION ABOUT THE SPRING SCALE AND THE NEWTON, LET’S GET SOME PRACTICE READING A SPRING SCALE.

•THE RED SCALE IS USED TO MEASURE LIGHTER OBJECTS AND HEAVIER OBJECTS CAN BE WEIGHED WITH THE BLUE SCALE.

•REMEMBER, IT IS IN EARTH’S GRAVITY THAT ONE NEWTON IS EQUAL TO ABOUT 100 GRAMS.•SO, IF THE VALUE OF GRAVITY CHANGED, SAY ON ANOTHER PLANET, THE VALUE OF THE NEWTON WOULD ALSO CHANGE.•THAT OFTEN MAKES THE CONCEPT OF WEIGHT UNSATISFACTORY FOR SCIENTIFIC WORK.

•FOR THEIR WORK, SCIENTISTS NEED INFORMATION ABOUT STUFF THAT DOES NOT CHANGE AS GRAVITY CHANGES.

•AND THEY FOUND IT IN THE CONCEPT CALLED....

MASS.

MEASURING MASS

• AGAIN, TO MEASURE MOST ANYTHING ONE NEEDS SOME TOOL WITH WHICH TO MEASURE AND A STANDARD UNIT OF MEASUREMENT.

•THE TOOL WE USE TO MEASURE MASS IS A BALANCE SCALE.

•THE STANDARD UNIT OF MEASUREMENT USED IN SCIENCE IS THE GRAM.

•BEFORE GOING INTO THE NITY GRITTY OF MEASURING MASS, WE NEED AN UNDERSTANDING OF JUST WHAT MASS IS.

•MASS IS THE AMOUNT OF MATTER IN AN OBJECT.

•MASS IS DIFFERENT THAN EITHER SIZE OR VOLUME.

•THE OBJECT ON THE LEFT, ALTHOUGH MUCH BIGGER, HAS JUST THE SAME MASS AS THE TWO SMALL ROCKS ON THE RIGHT.

•MASS IS MORE USEFUL TO SCIENTISTS THAN WEIGHT BECAUSE AN OBJECT’S MASS REMAINS CONSTANT REGARDLESS OF THE AMOUNT OF GRAVITY.

•THE REASON THAT THE MASS OF OBJECTS ON A BALANCE SCALE IS NOT AFFECTED BY CHANGES IN GRAVITY IS THAT THE SAME GRAVITY IS PULLING ON BOTH SIDES OF THE BALANCE.

•IF EACH TRAY HAS THE SAME AMOUNT OF MATTER...REGARDLESS OF SHAPE OR VOLUME.

GRAVITY PULLS EQUALLY ON EACH OF THEM AND THE TRAYS STAY BALANCED.

•BUT IF ONE OBJECT HAS MORE MASS THAN THE OTHER:

YOU KNOW WHAT’S GOING TO HAPPEN.

•SURE, THE MORE MASSIVE OBJECT, BEING PULLED HARDER BY GRAVITY, WILL GO DOWN AND THE LESS MASSIVE OBJECT WILL GO UP.

•IF WE BALANCE AND UNKNOWN OBJECT IN THE RED TRAY WITH KNOWN MASSES IN THE YELLOW TRAYWE WILL LEARN THE MASS OF THE OBJECT IN THE RED TRAY.

•BUT WHERE DO WE FIND THESE “KNOWN” MASSES?

WE USE PIECES OF BRASS MARKED WITH THEIR MASS AS STANDARD UNITS OF MASS.

•LIKE THESE:

•WE HAVE THE TOOL (A BALANCE SCALE) AND THE STANDARD UNIT (THE GRAM), THE ONLY OTHER THING WE NEED TO FIND THE MASS OF AN OBJECT IS A PROCEDURE.

•THE PROCEDURES IN THE FOLLOWING SLIDES ARE BASIC, BUT THEY WORK.

1. PLACE THE OBJECT IN ONE TRAY.

2. PLACE THE LARGEST MASS IN THE OTHER TRAY.

•THE 500g MASS IS THE GREATER THAN THE MASS OF THE PUMPKIN, SO REMOVE IT AND PLACE THE SECOND LARGEST PIECE OF STANDARD MASS.

3. PLACE THE SECOND LARGEST MASS IN THE OTHER TRAY.

•THE 200g MASS IS ALSO GREATER THAN THE MASS OF THE PUMPKIN, SO REMOVE IT AND PLACE THE THIRD LARGEST PIECE OF THE STANDARD MASS ON THE TRAY.

3. PLACE THE THIRD LARGEST MASS IN THE OTHER TRAY.

•AH, THE 100g MASS IS LESS THAN THE MASS OF THE PUMPKIN, SO LEAVE IT AND ADD THE NEXT LARGEST PIECE OF STANDARD MASS ON THE TRAY.

OK, THE 100g AND 50g MASSES ARE EQUAL TO THE MASS OF THE PUMPKIN.

•IT MAY TAKE A FEW MORE STEPS TO EXACTLY BALANCE THE MASS OF YOUR OBJECT.

•KEEP USING THE SAME PROCEDURE: ADD THE NEXT LARGEST UNIT AND IF THAT IS TOO MUCH, REMOVE IT AND SELECT THE NEXT LARGER UNIT.

•WHEN THE OBJECT AND THE MASS UNITS ARE BALANCED, LINE UP THE MASS UNITS FROM THE LARGEST TO THE SMALLEST.

•TOTAL THE VALUES OF THE THE MASS UNITS AND BINGO, YOU KNOW THE MASS OF THE OBJECT.

•THERE ARE SOME BALANCE SCALES WITH SLIDERS THAT CAN BE USED TO MOVE GRADUATED AMOUNTS OF MASS TO BALANCE THE OBJECT.

•THESE ALLOW THE MASS OF THE OBJECT TO BE READ DIRECTLY FROM THE SLIDERS.

•MORE ADVANCED BUT EVEN MORE DISTANT FROM “BALANCING” MASSES, IS THE TRIPLE BEAM BALANCE.

•YOU READ THIS SCALE BY NOTING WHERE THE SLIDER POINTERS ARE AND TOTALING THOSE NUMBERS.

RIGHT, 161 GRAMS

THERE YOU HAVE IT:

MEASURING WEIGHTAND MASS

•STUDY SCIENCE AND WHEN YOU GROW UP YOU MAY GET A CHANCE TO GO THE MOON WHERE:

•YOU CAN LEAP HIGH AND WEIGH LESS, BUT DON’T FORGET, YOUR MASS WILL STILL BE THE SAME.