Bellwork

• What is the difference between the variables “Fg”, “g” and “m”?

• “Fg” is the FORCE of gravity or WEIGHT

• “g” is the ACCELERATION of gravity

• “m” is the MASS of an object

Bellwork (cont.)

• The force of gravity “Fg” causes objects to accelerate “g”

• “Fg” is the PULL

• “g” is the MOTION

How to Use a Triple-Beam Balance

11/20/13

Scale vs. Balance

Scale vs. Balance

• A scale is used to measure the weight (force of gravity) of an object, it makes use of compression.

Unit - Newtons

• A balance is used to measure the mass of different objects.

Unit – grams or kilograms

Relationship Between Mass and Weight

• Remember mass and weight are two different quantities

• (weight) = (mass) X (acceleration of gravity)

Fg = m · g

Weight and Scales

• Weight will change if the acceleration of gravity is different (Earth vs. Moon)

Mass and Balances• Mass will not change if the acceleration of

gravity changes

Mass and Balances

Units

Parts of a Balance

Pan

Sliders ThumbscrewZeroMark

Back

Dial

Balance SetupBalance SetupMove the sliders and dial so that they

read ‘zero’.Make sure that there is nothing on the

pan.Check to see if the balance reads zero.

Massing the Bridge Place the bridge on the balance Move the sliders, beginning with the largest.

When moving a slider causes the balance to tip, move the slider back to the previous position.

Make sure that it is in a notch. Move the next slider until it tips the balance.

Place is in the previous position. Turn the dial until the balance reads zero. Read the mass. Remove bridge and reset the balance to zero.

Reading SlidersReading Sliders

Read each of the sliders and add their weights together.

The sliders indicate the mass is:

373 g

NextBack

Reading DialReading Dial

This measurement is past the eighth line following the 8 on the dial. This indicates a mass of:

378.9 g

Resources

• Erickson, John. "How to Use a Triple-Beam Balance." Web. 14 Nov. 2011. <http://www.csun.edu/~jte35633/lectures/balance.ppt>.

Bridge Analysis

• Due Wednesday 12/4/13

• Everyone needs to do an analysis

• 8 Questions

• 400 word creative story

– With 5 new bridge vocab. words

– Vocab. link will be on the website

Final Words on Bridges• Need a hole in the center

• Make sure you can get the load tester on your bridge in less then a minute

– Truss bridge

• Know how to use the balance you will be measuring it before the testing

• Can only use school glue – NO tape!

• String limit – total mass of the bridge with string has to be less than 60.0 g

Today• Work at the desks NOT in the lab area

At the end of class:

• Place bridge in period cabinet

• Return materials

• Clean up – glue, scrapes, etc. (last 5 min.)

• Yes, you can work on the bridge outside of class and over the weekend

• Need to be working on the project!