Mythbusters Mentos Fountain Is the Mentos Fountain a physical reaction or a chemical reaction? On your worksheet, complete a “Claim-Evidence-Reasoning” response to this question. Claim: make a simple declarative statement Evidence: present the data and/or observations that you will use to support your claim Reasoning: explain how and/or why your evidence supports your claim (refer to definitions, concepts, equations, etc. as appropriate)

Measurement in Science Measurements in science use the SI System To study motion and force, we need to measure: Mass – how much “stuff” there is Length – distances, areas, and volumes of space Time – how quickly or slowly something happens The fundamental units for these measurements: Mass – the gram (unit symbol = g) Length – the meter (unit symbol = m) Time – the second (unit symbol = s)

Avoiding Writer’s Cramp Sometimes our numbers get really big (think the size of the universe) or really small (think the size of electrons or other subatomic particles) We can use exponents of 10 to avoid writing lots of zeroes For example, 3 x 106 instead of 3,000,000 Or 5.6 x 10-9 instead of 0.0000000056 And we can add prefixes to the basic SI units to take the place of the exponents!!

SI Prefixes For larger things For smaller things Kilo- = 103 1 kg = 1,000 g (one thousand) Mega- = 106 1 Mm = 1,000,000 m (one million) Giga- = 109 1 Gs = 1,000,000,000 s (one billion) For smaller things Centi- = 10-2 1 cm = 1/100 m (1 one-hundredth) Milli- = 10-3 1 mL = 1/1000 L (1 one-thousandth) Micro- = 10-6 1 ug = 1/1,000,000 g (1 one-millionth) Nano- = 10-9 1 ns = 1/1,000,000,000 s (1 one-billionth)

Fluid Volumes – another option Volume is a length times a length times a length So, we could have volumes of m3, or km3, or mm3, or cm3 (sometimes written “cc”), etc. It happens that for fluids (liquids and gases), 1000 cc is a very convenient volume to use This volume is defined as 1 liter (unit symbol = L) Thus, 1 L = 1000 cc = 1000 cm3 = 1000 ml If the sides of a cube had a length of 10 cm, the volume of the cube would be 1 L Liters vs cubic meters is a matter of convenience

Measuring Mass On Earth, we can measure mass using a “spring scale” or a “balance” A spring scale balances the force of gravity on the object with the force of a stretched spring A balance balances the force of gravity on the object with the force of gravity on other masses

Spring Scale or Balance? If you were going to the moon and wanted to measure the mass of a moonrock while you were there, which device should you take along with you from Earth – a spring scale or a balance? On your worksheet, complete a “Claim-Evidence-Reasoning” response to this question. Claim: make a simple declarative statement Evidence: present the data and/or observations that you will use to support your claim Reasoning: explain how and/or why your evidence supports your claim (refer to definitions, concepts, equations, etc. as appropriate)